Dedicatedto

mywife,Jean,anddaughters,Lisa,Linda,andLori,andtheirfamilies,whosupportedmyeffortsthroughouttheyears

AbouttheAuthor:

JoeMascetta has taught high school chemistry for twenty years.Hewas thescience department coordinator and principal ofMt. Lebanon High School inPittsburgh, Pennsylvania. He also served as a science consultant to the areaschools and is a past-president of the Western Pennsylvania Association ofSupervision and Curriculum Development (ASCD) and the State AdvisoryCommitteeofASCD.Heholdsdegrees from theUniversityofPittsburgh, theUniversity of Pennsylvania, and Harvard University, and was a participant inHarvard Project Physics, a General Electric Science Fellowship to UnionCollege in Schenectady,NewYork, theChemicalBondApproachCurriculumStudy at Kenyon College, Ohio, and the Engineering Concepts CurriculumProjectandScienceCurriculumSupervisionattheUniversityofColorado.

©Copyright2010,2008,2006byBarron’sEducationalSeries,Inc.Prioreditions©Copyright2002,1998,1994byBarron’sEducationalSeries,Inc.,underthetitleHowtoPreparefortheSATII:Chemistry.Prioreditions©Copyright1990,1986,1981,1969byBarron’sEducationalSeries,Inc.,underthetitleHowtoPrepareforCollegeBoardAchievementTestinChemistry.

Allrightsreserved.Nopartofthisworkmaybereproducedordistributedinanyformorbyanymeanswithoutthewrittenpermissionofthecopyrightowner.

Allinquiriesshouldbeaddressedto:Barron’sEducationalSeries,Inc.250WirelessBoulevardHauppauge,NewYork11788www.barronseduc.com

eISBN:978-1-4380-8374-2Revisede-Pubpublication:August,2012

Contents

Introduction:AbouttheTest

ADIAGNOSTICTEST

ADiagnosticTest

AnswersandExplanationsCalculatingYourScoreDiagnosingYourNeedsPlanningYourStudyFinalPreparation—TheDayBeforetheTestAftertheTest

REVIEWOFMAJORTOPICS

1IntroductiontoChemistryMatterEnergyConservationofMassandEnergyScientificMethodMeasurementsandCalculationsChapterSummaryInternetResourcesPracticeExercises

2AtomicStructureandthePeriodicTableoftheElementsElectricNatureofAtomsAtomicSpectraTheWave-MechanicalModelSublevelsandElectronConfigurationTransitionElementsPeriodicTableoftheElementsPropertiesRelatedtothePeriodicTableNuclearTransformationsandStabilityTheNatureofRadioactiveEmissionsMethodsofDetectionofAlpha,Beta,andGammaRaysDecaySeries,Transmutations,andHalf-lifeRadioactiveDatingNuclearReactionsChapterSummaryInternetResourcesPracticeExercises

3BondingTypesofBondsIntermolecularForcesofAttractionDoubleandTripleBondsResonanceStructuresMolecularGeometry—VSEPR—andHybridizationSigmaandPiBondsPropertiesofIonicSubstancesPropertiesofMolecularCrystalsandLiquidsChapterSummaryInternetResourcesPracticeExercises

4ChemicalFormulasNamingandWritingChemicalFormulasOxidationStatesandFormulaWritingNamesandFormulasofCommonAcidsandBasesChemicalFormulas:TheirMeaningandUseLawsofDefiniteCompositionandMultipleProportionsWritingandBalancingSimpleEquationsShowingPhasesinChemicalEquationsWritingIonicEquationsChapterSummaryInternetResourcesPracticeExercises

5GasesandtheGasLawsSomeRepresentativeGasesGeneralCharacteristicsofGasesGasLawsandRelatedProblemsChapterSummaryInternetResourcesPracticeExercises

6Stoichiometry(ChemicalCalculations)andtheMoleConceptTheMoleConceptMolarMassandMolesMoleRelationshipsGasVolumesandMolarMassDensityandMolarMassMass–VolumeRelationshipsMass–MassProblemsVolume–VolumeProblems

ProblemswithanExcessofOneReactantoraLimitingReactantPercentYieldofaProductChapterSummaryInternetResourcesPracticeExercises

7Liquids,Solids,andPhaseChangesLiquidsPhaseEquilibriumBoilingPointCriticalTemperatureandPressureSolidsPhaseDiagramsWaterPolarityandHydrogenBondingSolubilityWaterSolutionsContinuumofWaterMixturesExpressionsofConcentrationDilutionColligativePropertiesofSolutionsCrystallizationChapterSummaryInternetResourcesPracticeExercises

8ChemicalReactionsandThermochemistryPredictingReactionsThermochemistryChangesinEnthalpy

AdditivityofReactionHeatsandHess’sLawChapterSummaryInternetResourcesPracticeExercises

9RatesofChemicalReactionsFactorsAffectingReactionRatesActivationEnergyReactionRateLawChapterSummaryInternetResourcesPracticeExercises

10ChemicalEquilibriumReversibleReactionsandEquilibriumLeChâtelier’sPrincipleEffectsofChangingConditionsEquilibriainHeterogeneousSystemsCommonIonEffectDrivingForcesofReactionsChapterSummaryInternetResourcesPracticeExercises

11Acids,Bases,andSaltsDefinitionsandPropertiesIndicatorsTitration—VolumetricAnalysisBufferSolutionsSaltsAmphotericSubstances

AcidRain—AnEnvironmentalConcernChapterSummaryInternetResourcesPracticeExercises

12Oxidation-ReductionandElectrochemistryOxidation-ReductionandElectrochemistryQuantitativeAspectsofElectrolysisBalancingRedoxEquationsChapterSummaryInternetResourcesPracticeExercises

13SomeRepresentativeGroupsandFamiliesSulfurFamilyHalogenFamilyNitrogenFamilyMetalsChapterSummaryInternetResourcesPracticeExercises

14CarbonandOrganicChemistryCarbonOrganicChemistryHydrocarbonsHydrocarbonDerivativesChapterSummaryInternetResourcesPracticeExercises

15TheLaboratoryLaboratorySafetyRulesSomeBasicSetupsSummaryofQualitativeTestsChapterSummaryInternetResourcesPracticeExercises

PRACTICETESTS

PracticeSubjectTestsinChemistry

PracticeTest1

AnswersandExplanationsforTest1CalculatingYourScoreDiagnosingYourNeeds

PracticeTest2

AnswersandExplanationsforTest2CalculatingYourScoreDiagnosingYourNeeds

PracticeTest3

AnswersandExplanationsforTest3CalculatingYourScoreDiagnosingYourNeeds

PracticeTest4

AnswersandExplanationsforTest4CalculatingYourScoreDiagnosingYourNeeds

APPENDIXES

ModernPeriodicTable

SomeImportantEquations

SomeUsefulTables

TheChemicalElements

Glossary

Introduction:AbouttheTest

The SAT Subject Tests are given in specific subject areas to assess youracademicabilitiesforcollege.TheyarepreparedbytheCollegeBoardandgiveevidence about your readiness in specific academic areas. The test cancomplement and enhanceyour college admission credentials.The introductionofthisbookwillgiveyouallthebasicinformationyouneedtoknowaboutthesubject test in chemistry. To learn additional information about this testingprogram,go to thewebsitewww.collegeboard.organd lookunderSATSubjectTestsAlloftheSATSubjectTestsarecontainedinthesametestbooklet.Eachtakes

1houroftestingtime,andyoumaychooseanyone,two,orthreeteststotakeatonesitting.ManycollegesrequireorrecommendoneormoreSubjectTestsforadmission

orplacement.Thescoresareusedinconjunctionwithyourhighschoolrecord,resultsontheSAT,teacherrecommendations,andotherbackgroundinformationto provide a reliable measure of your academic achievements and a goodpredicationofyourfutureperformance.Inadditiontoobtainingastandardizedassessmentofyourachievementfrom

yourscores,somecollegesusethetestresultsforplacementintotheirparticularprograms in the freshman year. At others, advisers use the results to guidefreshmenintheselectionofcourses.

IstheSATSubjectTestinChemistryRequired?The best information on whether SAT Subject Tests are required and, if so,whichonesisfoundintheindividualcollegecatalogsoradirectoryofcolleges.Some colleges specify which tests you must take, while others allow you tochoose.Obviously, ifyouhaveachoiceandyouhavedonewell inchemistry,youshouldpicktheSATSubjectTestinChemistryasoneofyourtests.Evenif

thetest isnotrequiredbythecollegestowhichyouareapplying,youcanaddtheresulttoyourrecordtosupportyourachievementlevel.

WhenShouldYouTaketheTest?You will undoubtedly do best if you take the test after completing the highschool chemistry course or courses that you plan to take. At this time, thematerialwillbefreshinyourmind.Forgettingbeginsveryquicklyafteryouarepastatopicorhavefinishedthecourse.Youshouldplanareviewprogramforatleastthelast6weeksbeforethetestdate.(Aplanisprovidedlaterinthisbookforsuchareview.)Carefulreviewdefinitelyhelps—crammingjustwillnotdoifyouwanttogetthebestscoreofwhichyouarecapable!Colleges thatuseSATSubjectTest resultsaspartof theadmissionsprocess

usuallyrequirethatyoutakethetestnolaterthanDecemberorJanuaryofyoursenior year. For early-decision programs, the test time is June of your junioryear. Since chemistry is often a junior year course, June of that year is theoptimumtimetotakethetest.

WhenIstheTestOffered?ThechemistrytestisavailableeverytimetheSATSubjectTestsaregiven,thatis,onthefirstSaturdayofOctober,November,December,May,andJune.Theyarealsogivenon the lastSaturdayof January.Besure that the testingsite forwhich you plan to register offers the SAT Subject Tests on each of these sixtimes.Rememberthatyoumaychoosetotakeoneortwoadditionaltestsbesideschemistryon anyone test day.Youdohave to specify in advancewhich testsyouplan to takeon the testdateyouselect;however,except for theLanguageTestwithListening,youmaychangeyourmindonthedayofthetest.

HowDoYouRegister?You may get all of your registration information by going tosat.collegeboard.org/register/how to register. This is the quickest and easiestwaytoregisterforthetest.Thissitewillgiveyoualltheinformationyouneedtocompleteyourregistration.Youcanchooseyourtestdateandcenteraswellas receive immediate registration confirmation. This website also gives youinstructionsforhowtoregisterbymail.

Thedeadlineforregistrationisapproximatelyonemonthbeforethetestdate.

HowShouldYouPreparefortheTest?Barron’sSATSubjectTestinChemistrywillbeveryhelpful.Themoreyouknowaboutthetest,themorelikelyyouaretogetthebestscorepossibleforyou.Thisbookprovidesyouwithadiagnostictest,scoringinformation,fourpracticetestsand the equivalent ofonemore test incorporatedwith the chapter review teststhat allowyou to become familiarwith the question types and thewordingofdirections,andtogainafeelforthedegreeofemphasisonparticulartopicsandtheways inwhich informationmaybe tested.Eachof theseaspects shouldbeconsciouslypursuedasyouusethisbook.

WhatTopicsAppearontheTest,andtoWhatExtent?Thefollowingchartsshowthecontentofthetestandthelevelsofthinkingskillstested:

Note:Eachtestcontainsapproximatelyfivequestionsonequationbalancingand/orpredictingproductsofchemicalreactions.Thesearedistributedamongthevariouscontentcategories.

Thefirstchartgivesyouageneraloverviewof thecontentof the test.Yourknowledgeofthetopicsandyourskillsinrecalling,applying,andsynthesizingthis knowledge are evaluated through 85 multiple-choice questions. Thismaterial is that generally covered in an introductory course in chemistry at alevelsuitable forcollegepreparation.Whileevery testcovers the topics listed,different aspects of each topic are stressed from year to year.Add to this thedifferences that exist in high school courseswith respect to the percentage oftimedevotedtoeachmajortopicandtothespecificsubtopicscovered,andyoumay find that there are questions on topics with which you have little or nofamiliarity.Each of the sample tests in this book is constructed to match closely the

distributionoftopicsshownintheprecedingchartsothatyouwillgainafeelforthe makeup of the actual test. After each test, a chart will show you whichquestionsrelatetoeachtopic.Thiswillbeveryhelpfultoyouinplanningyourreviewbecauseyoucanidentifytheareasonwhichyouneedtoconcentrateinyourstudies.Anotherchartenablesyoutoseewhichchapterscorrespondtothevarioustopicareas.

WhatGeneralInformationShouldYouHaveAbouttheTest?1.Aperiodicchartisprovidedinthistestasaresourceandasthesourceof

atomicnumbersandatomicmassesoftheelements.

2.Youwillnotbeallowedtouseanelectroniccalculatorduringthetest.

3.Mathematicalcalculationsarelimitedtosimplealgebraicandnumericalones.

4.Youshouldbefamiliarwiththeconceptsofratiosandofdirectandinverseproportions,scientificnotation,andexponentialfunctions.

5.Metricsystemunitsareusedinthistest.

6.Thetestiscomposedofthreetypesofquestionsasexplainedinthenextsection.

WhatTypesofQuestionsAppearontheTest?TherearethreegeneraltypesofquestionsontheSATSubjectTestinChemistry— matching questions, true/false and relationship analysis questions, andgeneral five choice questions. This section will discuss each type and givespecific examples of how to answer these questions. You should learn thedirectionsforeach typeso thatyouwillbe familiarwith themon the testday.Thedirectionsinthissectionaresimilartothoseonthetest.

TYPE1.MATCHINGQUESTIONSINPARTA.Ineachofthesequestions,youaregivenfiveletteredchoicesthatyouwillusetoanswerallthequestionsin that set. The choices may be in the form of statements, pictures, graphs,experimental findings, equations, or specific situations. Answering a questionmay be as simple as recalling information or as difficult as analyzing theinformationgiventoestablishwhatyouneedtodoqualitativelyorquantitativelyto synthesizeyouranswer.Thedirections for this typeofquestion specificallystatethatachoicemaybeusedonce,morethanonce,ornotatallineachset.

PartA

Directions: Every set of the given choices below refers to the numberedstatements or formulas immediately following it.Choose the one letteredchoice that best fits each statement or formula and then fill in thecorresponding oval on the answer sheet. Each choicemay be used once,morethanonce,ornotatallineachset.

EXAMPLE

Questions1–3refertothefollowinggraphs:

1.Thegraphthatbestshowstherelationshipofvolumetotemperatureforanidealgaswhilethepressureisheldconstant

2.Thegraphthatbestshowstherelationshipofvolumetopressureforanidealgaswhilethetemperatureisheldconstant

3.Thegraphthatbestshowstherelationshipofthenumberofgramsofsolutethatissolublein100gramsofwateratvaryingtemperaturesifthesolubilitybeginsasasmallquantityandincreasesslowlyasthetemperatureisincreased

These three questions require you to recall the basic gas laws and the graphicdepictionoftherelationshipexpressedineachlaw,aswellashowsolubilitycanbeshowngraphically.Toanswerquestion1,youmustrecognizethattherelationshipofgasvolume

to changes in temperature is a direct relationship that is depicted by graphingCharles’s Law:V1/T1 =V2/T2. The only graph that shows that type of directrelationshipwiththeappropriateslopeis(A).Toanswerquestion2,youneedtounderstandthatBoyle’sLawstatesthatthe

pressureofagasisinverselyproportionaltothevolumeatconstanttemperature.Mathematically,thismeansthatpressure(P)timesvolume(V)isaconstant,orP1V1=P2V2.This inverselyproportional relationship is accuratelydepicted in(C).Although(B)showsthevaluesonthex-axisincreasingasthey-axisvaluesdecrease,itdoesnotfitthegraphforaninverseproportion.Question3requiresthatyouhaveknowledgeaboutsolubilitycurvesandcan

applythesolubilityrelationshipgiveninwordstograph(E).

TYPE2.TRUE/FALSEANDRELATIONSHIPQUESTIONSINPARTB.On the actual SAT Subject Test in Chemistry, this type of question must beansweredinaspecialsectionofyouranswersheetlabeled“chemistry.”Type2

questions are numbered beginning with 101. Each question consists of astatementorassertionincolumnIand,ontheothersideofthewordBECAUSE,another statement or assertion in column II. Your first task is to determinewhethereachofthestatementsistrueorfalseandtorecordyouranswerforeachintheanswerblocksforcolumnIandcolumnIIintheanswergridbydarkeningeither the or the oval.Hereyoumustuseyour reasoningskillsandyourunderstanding of the topic to determine whether there is a cause-and-effectrelationshipbetweenthetwostatements.

Herearethedirectionsandtwoexamplesofarelationshipanalysisquestion.

PartB

Directions: Every question below contains two statements, I in the left-handcolumnandIIintheright-handcolumn.Foreachquestion,decideifstatementIistrueorfalseandifstatementIIistrueorfalseandfillinthecorrespondingTorFovalsonyouranswer sheet.Fill inovalCEonly ifstatementIIisacorrectexplanationofstatementI.

SampleAnswerGrid:

CHEMISTRY*FillinovalCEonlyifIIisacorrectexplanationofI.

EXAMPLE1

101. When 2 liters of oxygengasreactcompletelywith2liters of hydrogen gas, thelimiting factor is thevolumeoftheoxygen

BECAUSE

thecoefficientsinthebalancedequationofagaseousreactiongivethevolumerelationshipofthereactinggases.

Thereactionthattakesplaceis

2H2+O2→2H2O

Thecoefficientsofthisgaseousreactionshowthat2Lofhydrogenreactwith1Lofoxygen,leaving1Lofunreactedoxygen.Thelimitingfactoristhequantityofhydrogen.TheabilitytosolvethisquantitativerelationshipshowsthatstatementIisnot

true. However, statement II does give a true statement of the relationship ofcoefficientsinabalancedequationofgaseouschemicalreaction.Therefore,theanswerblockswouldbecompletedlikethis:

EXAMPLE2

102.Water is agood solventofionicandpolarcompounds BECAUSE

thewatermoleculehaspolarpropertiesduetothefactorsinvolvedinthebondingofthehydrogenandoxygenatoms.

Statement I is true because water is such a good solvent that, as you haveprobably learned, it is sometimes referred to as the universal solvent. Thisproperty is attributed mostly to its polar structure. The polar covalent bondbetween the oxygen and hydrogen atoms and the angular orientation of thehydrogens at 105 degrees between them contribute to the establishment of apermanentdipolemomentinthewatermolecule.Thisalsogivesrisetoahighdegree of hydrogen bonding. These properties combine to make water apowerful solvent for both polar and ionic compounds. Because of yourfamiliaritywith these concepts and the processes bywhich substances go intosolution,youknowthatstatementIInotonly is truebutalso is thereasonthatstatement I is true. There is a cause-and-effect relationship between the twostatements.Therefore,theanswerblockswouldbemarkedlikethis:

TYPE3:GENERALFIVE-CHOICEQUESTIONSINPARTC.The five-choice items in Part C are written usually as questions but sometimes asincomplete statements. You are given five suggested answers or completions.Youmustselect theonethat isbest ineachcaseandrecordyourchoiceintheappropriateoval.Insomequestionsyouareaskedtoselecttheoneinappropriateanswer.Suchquestionscontainawordincapitalletters,suchasNOT,LEAST,orEXCEPT.

Insomeofthesequestions,youmaybeaskedtomakeanassociationbetweenagraphic,pictorial,ormathematical representationanda statedexplanationorproblem. The solution may involve solving a scientific problem by correctlyinterpreting the representation. In some cases the same representationmay beused fora seriesof twoormorequestions. Innocase,however, is thecorrectanswertoonequestionnecessaryforansweringasubsequentquestioncorrectly.Eachquestioninthesetisindependentoftheothers.

PartC

Directions:Everyquestionor incompletestatementbelowis followedbyfivesuggestedanswersorcompletions.Choosetheonethatisbestineachcaseandthenfillinthecorrespondingovalontheanswersheet.Remembertoreturntotheoriginalpartoftheanswersheet.

EXAMPLE1

40.Inthisgraphicrepresentationofachemicalreaction,whicharrowdepictstheactivationenergy?

(A)A(B)B(C)C

(D)D(E)E

Toanswerthisquestion,youneedtoknowhowtointerprettheenergylevelsinthisgraphicrepresentationofenergy-levelchangesalongthetimecontinuumofthe reaction. The activation energy is the minimum energy required for achemical reaction to take place. The reactant molecules come together, andchemical bonds are stretched, broken, and formed in producing the products.During this process the energy of the system increases to a maximum, thendecreases to theenergyof theproducts.Theactivationenergyis thedifferencebetweenthemaximumenergyandtheenergyofthereactants.Choice(C)inthegraphic depiction shows this energy barrier that has to be overcome for thereaction to proceed. The corresponding oval on the answer sheet should bedarkened.

EXAMPLE2

41.IfthemolarmassofNH3is17g/mol,whatisthedensityofthiscompoundatSTP?

(A)0.25g/L(B)0.76g/L(C)1.25g/L(D)3.04g/L(E)9.11g/L

Thesolutionof thisquantitativeproblemdependsontheapplicationofseveralprinciples.Oneprincipleisthatthemolarmassofagasexpressedingrams/molewilloccupy22.4Latstandardtemperatureandpressure(STP).Theotheristhatthe density of a gas at STP is themass of 1L of the gas. Therefore, 17 g ofammonia(NH3)willoccupy22.4L,and1Lisequalto17g/22.4Lor0.76g/L.Thecorrectansweris(B).

EXAMPLE3

Some questions in this part are followed by three or four bits of informationlabeledbyRomannumeralsIthroughIIIorIV.Oneormoreofthesestatementsmay correctly answer the question. You must select from the five letteredchoicestheonethatbestanswersthequestion.

42.Whichbond(s)is(are)ionic?I.H–Cl(g)II.S–Cl(g)III.Cs–F(g)(A)Ionly(B)IIIonly(C)IandIIonly(D)IIandIIIonly(E)I,II,andIII

Todeterminethetypeofbondingthatexistsinthesethreesubstances,youmustuseyourknowledgeofionicbondsandthewaytheyareformed.Youmustalsouseyourknowledgeoftherelationshipoftheelectronegativityofanelementandthepositionofthatelementintheperiodicchart.CompoundsIandIIareformedfrom elements that do not have enough difference in their respectiveelectronegativitiestocausetheformationofanionicbond.Thiscanbeinferredbychecking thepositionsof theelements (H,Cl, andS) in thePeriodicTableandnotinghowelectronegativityvarieswithanelement’spositioninthetable.Compound III, cesium fluoride, consists of elements that appear in the lowerright corner and the upper left corner, respectively, of the Periodic Table;therefore, thedifferenceintheirelectronegativityvaluesissufficientsothatanionicbondcanbepredictedbetween them.Of thechoicesgiven,only(B) isacorrectanswer.

HowCanYouUseThisBooktoPreparefortheTest?Thebestwaytousethisbookisatwo-stageapproach,andthenextsectionsarearranged accordingly.First, you should take the diagnostic test.Thiswill giveyouapreliminaryexposuretothetypeoftestyouareplanningtotake,aswellas

ameasure of howwell you achieve on each of the three parts. Youwill alsobecome aware of the types of questions that the test includes. Use the test-scoring information following the diagnostic test to determine your raw scoreandyourstrengthsandweaknessesinthespecificareasofthetest.Havingtakenthediagnostictest,youshouldthenfollowastudyprogram.A

studyplancoveringthe6weeksbeforethetesthasbeendevelopedforyouandisgivenindetailon.

FiveStepstoImproveYourProblem-SolvingSkills*Chemistry is a subject that deals with many problem situations that you, thestudent, must be able to solve. Solving problems may seem to be a naturalprocesswhenthedegreeofdifficultyisnotverygreat,andyoumaynotneedastructuredmethodtoattacktheseproblems.However,forcomplexproblemsanorderlyprocessisrequired.Thefollowingissuchaproblem-solvingprocess.Eachstepisvitaltothenext

stepandtothefinalsolutionoftheproblem.

Step1.Clarifytheproblem:toseparatetheproblemintothefacts,theconditions,andthequestionsthatneedtobeanswered,andtoestablishthegoal.

Step2.Explore:toexaminethesufficiencyofthedata,toorganizethedata,andtoapplypreviouslyacquiredknowledge,skills,andunderstanding.

Step3.Selectastrategy:tochooseanappropriatemethodtosolvetheproblem.

Step4.Solve:toapplytheskillsneededtocarryoutthestrategychosen.

Step5.Review:toexaminethereasonablenessofthesolutionthroughestimationandtoevaluatetheeffectivenessoftheprocess.

Thestepsof theproblem-solvingprocess listedaboveshouldbefollowedinsequence.Thesubskillslistedbelowforeachstep,however,arenotinsequence.Theorder inwhichsubskillpatternsareusedwilldifferwith thenatureof theproblem and/or with the ways in which the individual problem solver thinks.Also,noteverysubskillneedbeemployedinsolvingeveryproblem.

1.CLARIFYTHEPROBLEM

a.Identifythefacts.Whatisknownabouttheproblem?

b.Identifytheconditions.Whatisthecurrentsituation?

c.Identifythequestions.Whatneedstobeansweredbeforetheproblemcanbesolved?

d.Visualizetheproblem.

1.Makementalimagesoftheproblem.

2.Ifdesirableornecessary,drawasketchordiagram,makeanoutline,writedownsymbolsorequationsthatcorrespondtothementalimages.

e.Establishthegoal.Thegoaldefinesthespecificresulttobeaccomplishedthroughtheproblem-solvingprocess.Itdefinesthepurposeorfunctionthesolutionisexpectedtoachieveandservesasthebasisforevaluatingthesolution.

2.EXPLORE

a.Reviewpreviouslyacquiredknowledge,skills,andunderstanding.Determinewhetherthecurrentproblemissimilartoapreviouslyseentype.

b.Estimatethesufficiencyofthedata.Doesthereseemtobeenoughinformationtosolvetheproblem?

c.Organizethedata.Therearemanywaysinwhichdatacanbeorganized.Someexamplesareoutline,writtensymbolsandequations,chart,table,graph,map,diagram,anddrawing.Determinewhetherthedataorganizedintheway(s)youhavechosenwillenableyoutopartiallyorcompletelysolvetheproblem.

d.Determinewhatnewdata,ifany,needtobecollected.Whatadditionalinformationmaybeneededtosolvetheproblem?Cantheexistingdatabereorganizedtogeneratenewinformation?Dootherresourcesneedtobeconsulted?Thisstepmaysuggestpossiblestrategiestobeusedtosolvetheproblem.

3.SELECTASTRATEGY

Astrategyisagoal-directedsequenceofmentaloperations.Selectingastrategyis the most important and also the most difficult step in the problem-solving

process.Althoughtheremaybeseveralstrategiesthatwillleadtothesolutionofaproblem,theskilledproblemsolverusesthemostefficientstrategy.Thechoiceofthemostefficientstrategyisbasedonknowledgeandexperienceaswellasacareful application of the clarify and explore steps of the problem-solvingmethod.Someproblemsmayrequiretheuseofacombinationofstrategies.Thefollowingsearchmethodsmayhelpyoutoselectastrategy.Theydonot

representallof thepossiblewaysinwhichthiscanbedone.Othermethodsofstrategyselectionarerelatedtospecificcontentareas.

a.Trial-and-errorsearch:Suchasearcheitherdoesn’thaveordoesn’tuseinformationthatindicatesthatonepathismorelikelytoleadtothegoalthananyotherpath.

Trial-and-errorsearchcomesintwoforms,blindandsystematic.Inblindsearch,thesearcherspickpathstoexploreblindly,withoutconsideringwhethertheyhavealreadyexploredthesepaths.Apreferablemethodissystematicsearch,inwhichthesearcherskeeptrackofthepathstheyhavealreadyexploredanddonotduplicatethem.Becausethismethodavoidsmultiplesearches,systematicsearchisusuallytwiceasefficientasblindsearch.

b.Reductionmethod:Thisinvolvesbreakingtheproblemintoasequenceofsmallerpartsbysettingupsubgoals.Subgoalsmakeproblemsolvingeasierbecausetheyreducetheamountofsearchrequiredtofindthesolution.

Youcansetupsubgoalsbyworkingpartwayintoaproblemandthenanalyzingthepartialgoaltobeachieved.Indoingthis,youcandroptheproblemrestrictionsthatdonotapplytothesubgoal.Byaddingupallthesubgoals,youcansolvethe“abstracted”problem.

c.Workingbackward:Whenyouhavetroublesolvingaproblemhead-on,itisoftenusefultotrytoworkbackward.Workingbackwardinvolvesasimplechangeinrepresentationorpointofview.Yournewstartingpointistheoriginalgoal.Workingbackwardcanbehelpfulbecauseproblemsareofteneasiertosolveinonedirectionthananother.

d.Knowledge-basedmethod:Thisstrategyusesinformationstoredintheproblemsolver’smemory,ornewlyacquiredinformation,toguidethesearchforthesolution.Theproblemsolvermayhavesolvedasimilar

problemandcanusethisknowledgeinanewsituation.Inothercases,problemsolversmayhavetoacquireneededknowledge.Forexample,theymaysolveanauxiliaryproblemtolearnhowtosolvetheonetheyarehavingdifficultywith.

Searchingforanalogous(similar)problemsisaverypowerfulproblem-solvingtechnique.Whenyouarehavingdifficultywithaproblem,trytoposearelated,easieroneandhopetherebytolearnsomethingthatwillhelpyousolvetheharderproblem.

4.SOLVE

Use the strategy chosen to actually solve the problem. Executing the solutionprovides you with a very valuable check on the adequacy of your plan.Sometimesstudentswilllookataproblemanddecidethat,sincetheyknowhowto solve it, they need not bother with the drudgery of actually executing thesolution. Sometimes the students are right, but at other times they miss anexcellentopportunitytodiscoverthattheywerewrong.

5.REVIEW/VERIFYWITHESTIMATION

a.Evaluation.Thecriticalquestioninevaluationisthis:“DoestheanswerIproposemeetallofthegoalsandconditionssetbytheproblem?”Thus,aftertheeffortoffindingasolution,youmustturnbacktotheproblemstatementandcheckcarefullytobesureyoursolutionsatisfiesit.

Witheasyproblemsthereisastrongtemptationtoskipevaluationbecausetheprobabilityoferrorseemssmall.Insomecases,however,thiscanbecostly.Evaluationmayprovethaterrorswerepresent.

b.Verificationofthereasonablenessoftheanswer.Itiseasytobecomesoinvolvedwiththeprocessandmathematicsofaproblemthatananswerisrecordedthatistotallyillogical.Toavoidthismistake,youshouldsimplifythenumbersinvolvedandsolveforananswer.Havingdonethis,compareyourestimatedresultwithyouranswertoensurethatyouranswerisfeasible.

Forexample,aproblemrequiresthefollowingoperations:

5.12×105×3.98×106dividedby910

Anddoingallthemath,yougetananswerof

0.02239×1011or2.24×109

To estimate the answer, first simplify the numbers to one significant figure(significantfiguresarediscussedinChapter1).Thisgives

5×105×4×106dividedby9×102

whichis

20×1011dividedby9×102=2.2×109

Thisistheestimatedanswer,whichvalidatestheanswerabove.Whenyou are dealingwith test items that providemultiple-choice answers,

you can often use estimation to arrive at the answer without doing the morecomplicatedmathematics.

c.Consolidation.Herethebasicquestiontobeansweredis:“WhatcanIlearnfromtheexperienceofsolvingthisproblem?”Thefollowingmorespecificquestionsmayhelpyoutoanswerthisgeneralone:

1.Whywasthisproblemdifficult?

2.Wasitdifficulttofollowaplan?

3.Wasitdifficulttodecideonaplan?Ifso,why?

4.DidItakethelongwaytotheanswer?

5.CanIusethisplanagaininsimilarproblems?

Theimportant thingis toreflectontheprocessthatyouusedinorder tomakefutureproblemsolvingeasier.

USETHISPERIODICTABLEWITHALLTHEPRACTICETESTS.

*AdaptedwithpermissionfromThinkingSkillsResourceGuide,anoncopyrightedpublicationofMountLebanonSchoolDistrict,Pittsburgh,PA.

PART1

ADIAGNOSTICTEST

ADiagnosticTest

Thefollowingtestof85questionsisasampleoftheactualtestyouwilltaketomeasure your chemistry achievement. It has basically the same distribution oftopics, directions, and number and types of questions. Before taking this test,readtheadvicegiveninthesectionentitled“FinalPreparation—TheDayBeforetheTest.”Usetheanswersheetprovided,andlimitthetesttimeto1hour.APeriodicTableoftheElementshasbeenincludedforyouruseonproblems

requiringthissourceofinformation.Usethistablealsowiththepracticetestsattheendof thebook.TheDiagnosticTestquestions containhyperlinks to theiranswersandexplanations.Simplyclickonthequestionnumbers tomovebackandforth.Turnnowtothetest.

** Since this is an eBook, please record all of your answers separately.DirectionsintheDiagnosticTestdoreflectthosesimilartowhatappearsontheexam.AllAnswerSheetsshouldbeusedforreferenceonly.

AnswerSheetDIAGNOSTICTEST

Determine the correct answer for each question. Then, using a No. 2pencil,blackencompletelytheovalcontainingtheletterofyourchoice.AllAnswer Sheets are for reference only. Please record your answersseparately.

THEDIAGNOSTICTESTNote:Forallquestionsinvolvingsolutions,youshouldassumethatthesolventiswaterunlessotherwisenoted.Reminder:Youmaynotuseacalculatoronthistest!

Thefollowingsymbolshavethemeaningslistedunlessotherwisenoted.

H=enthalpy g=gram(s)M=molar J=joules(s)n=numberofmoles kJ=kilojoulesP=pressure L=liter(s)R=molargasconstant mL=milliliter(s)S=entropy mol=mole(s)mm=millimeter(s) T=temperatureV=volt(s) V=volumeatm=atmosphere

PartA

Directions: Every set of the given lettered choices below refers to thenumbered statements or formulas that immediately follow it. Choose theoneletteredchoicethatbestfitseachstatementorformula;thenfillinthecorresponding oval on the answer sheet. Each choicemay be used once,morethanonce,ornotatallineachset.

Questions1–4refertothefollowingelements:

(A)Fluorine(B)Chlorine(C)Bromine(D)Iodine

(E)Astatine

1.Theelementthatismostactivechemically

2.Theelementwiththesmallestionicradius

3.Theelementwiththelowestfirstionizationpotential

4.Theelementthatfirstshowssomevisiblemetallicpropertiesatroomtemperature

Questions5–7refertothefollowingsublevels:

(A)1s(B)2s(C)3s(D)3p(E)3d

5.Containsupto10electrons.

6.Containsonepairofelectronsintheground-stateelectronconfigurationofthelithiumatom.

7.Isexactlyone-halffilledintheground-stateelectronconfigurationofthephosphorusatom.

Questions8–12refertothefollowing:

(A)Avogadro’snumber(B)P1V1=P2V2(C)V1T2=V2T1(D)Dalton’sTheory(E)Gay-Lussac’sLaw

8.Proposesbasicpostulatesconcerningelementsandatoms

9.Proposesarelationshipbetweenthecombiningvolumesofgaseswithrespecttothereactantsandgaseousproducts

10.Proposesatemperature-volumerelationshipofgases

11.Proposesaconceptregardingthenumberofparticlesinamole

12.Proposesavolume-pressurerelationshipofgases

Questions13–16refertothefollowingstructures:

(A)R–OH(B)R–O–R*

(C)

(D)

(E)

(*AlkylgroupthatisnotnecessarilythesameasR)

13.Theorganicstructuredesignationthatincludesthefunctionalgroupofanaldehyde

14.Theorganicstructuredesignationthatincludesthefunctionalgroupofanacid

15.Theorganicstructuredesignationthatincludesthefunctionalgroupofanester

16.Theorganicstructuredesignationthatincludesthefunctionalgroupofanether

Questions17–21refertothefollowing:

(A)H2(g)(B)CO2(g)(C)2N2O(g)(D)2NaCl(aq)(E)H2SO4(diluteaq)

17.Theexpressionthatcanbeusedtodesignatealinearnonpolarmoleculethatcontainspolarbonds

18.Theexpressionthatcanbeusedtodesignate2molesofatoms

19.Theexpressionthatcanbeusedtodesignate3molesofatoms

20.Theexpressionthatcanbeusedtodesignateamaximumof3molesofions

21.Theexpressionthatcanbeusedtodesignate6molesofatoms

Questions22–25refertothefollowingpairsofsubstances:

(A)NH3andN2H4

(B)16Oand17O(C)NH4ClandNH4NO3

(D)CH3OCH3andCH3CH2OH(E)O2andO3

22.Areisotopes

23.Havebothionicandcovalentbonds

24.Allallotropes

25.Arestrongelectrolytesinaqueoussolutions

PartB

ON THE ACTUAL SAT SUBJECT TEST IN CHEMISTRY, THEFOLLOWING TYPE OF QUESTION MUST BE ANSWERED ON ASPECIAL SECTION (LABELED “CHEMISTRY”) AT THE LOWERLEFT-HAND CORNER OF YOUR ANSWER SHEET. THESEQUESTIONSARENUMBEREDBEGINNINGWITH101ANDMUSTBEANSWEREDACCORDINGTOTHEFOLLOWINGDIRECTIONS.

Directions:Every question below contains two statements, I in the left-handcolumnandIIintheright-handcolumn.Foreachquestion,decideifstatementIistrueorfalseandwhetherstatementIIistrueorfalse,andfillin thecorrespondingTorFovalsonyouranswersheet.*Fill inovalCEonlyifstatementIIisacorrectexplanationofstatementI.

SampleAnswerGrid:

CHEMISTRY*FillinovalCEonlyifIIisacorrectexplanationofI.

I II

101. Acatalystcanaccelerateachemicalreaction

BECAUSEacatalystcandecreasetheactivationenergyrequiredforthereactiontooccur.

102. Moltensodiumchlorideisagoodelectricalconductor

BECAUSEsodiumchlorideinthemoltenstateallowsionstomovefreely.

103. Iceislessdensethanliquidwater

BECAUSE watermoleculesarenonpolar.

104.Twoisotopesofthesameelementhavethesamemassnumber

BECAUSEisotopeshavethesamenumberofprotons.

105.

A1.0gsampleofcalciumcitrate,Ca3(C6H5O7)2(molarmass498g/mol),containsmoreCathana1.0gsampleofcalciumcarbonate,CaCO3(molarmass100g/mol)

BECAUSE

therearemoreCaatomsin1.0molofcalciumcarbonatethanin1.0molofcalciumcitrate.

106.TwolitersofCO2canbeproducedby1gramofcarbonburningcompletely

BECAUSE

theamountofgasevolvedinachemicalreactioncanbedeterminedbyusingthemolerelationshipofthecoefficientsinthebalancedequation.

107. Areactionisatequilibriumwhenitreachescompletion

BECAUSE

theconcentrationsofthereactantsinastateofequilibriumequaltheconcentrationsoftheproducts.

108.

Theanionsinanelectrolyticcellmigratetothecathode

BECAUSE

positivelychargedionsareattractedtothenegativelychargedcathodeinan

electrolyticcell

109.

AsolutionwithpH=5hasahigherconcentrationofhydroniumionsthanasolutionwithapH=3

BECAUSE pHisdefinedas−log[H+].

110. Anendothermicreactioncanbespontaneous

BECAUSE

boththeenthalpyandtheentropychangesaffecttheGibbsfree-energychangeofthereaction.

111.Weakacidshavesmallvaluesfortheequilibriumconstant,Ka,

BECAUSE

theconcentrationofthehydroniumionisinthenumeratoroftheKaexpression.

112. OnemoleofNaClcontains2molesofions

BECAUSE NaClisastablesaltatroomtemperature.

113.

Apibondisformedbetweenthelobesofadjacentporbitalsinthesameplaneoftwoatomsthatcontainonlyoneelectroneach

BECAUSE

eachofthetwolobesofasingleporbitalcanholdtwoelectronsofoppositespin.

114.H2SandH2Ohaveasignificantdifferenceintheirboilingpoints

BECAUSEhydrogensulfidehasahigherdegreeofhydrogenbondingthanwater.

PartC

Directions:Everyquestionor incompletestatementbelowis followedbyfivesuggestedanswersorcompletions.Choosetheonethatisbestandthenfillinthecorrespondingovalontheanswersheet.

26.Twoimmiscibleliquids,whenshakentogethervigorously,mayform(A)asolution

(B)atincture(C)asediment(D)ahydratedsolution(E)acolloidaldispersion

27.Athermometerisusedtorecordthecoolingofaconfinedpuresubstanceoveraperiodoftime.Duringwhichintervalonthecoolinggraphaboveisthesystemundergoingachangeofstatefromaliquidtoasolid?

28.Ifaprincipalenergylevelofanatominthegroundstatecontains18electrons,theywillbearrangedinorbitalsaccordingtothepattern

(A)s6p6d6

(B)s2p6d10

(C)s2d6f10

(D)s2p6f10

(E)s2p2f14

29.Whichofthefollowingmoleculesisasaturatedhydrocarbon?

(A)C3H8

(B)C2H4

(C)C4H6

(D)CH3OH(E)CH3COOH

30.Aliterofhydrogenisat5.0°Ctemperatureandunder640.torrpressure.Ifthetemperaturewereraisedto60.0°Candthepressuredecreasedto320.torr,howwouldthelitervolumebemodified?

31.Ofthefollowingstatementsaboutthenumberofsubatomicparticlesinanionof ,whichis(are)true?

I.16protonsII.14neutronsIII.18electrons

(A)IIonly(B)IIIonly(C)IandIIonly(D)IandIIIonly(E)I,II,andIII

32.Themostactivemetallicelementsarefoundin

(A)theupperrightcorneroftheperiodicchart(B)thelowerrightcorneroftheperiodicchart(C)theupperleftcorneroftheperiodicchart(D)thelowerleftcorneroftheperiodicchart(E)themiddleoftheperiodicchart,justbeyondthetransitionelements

33.If1moleofeachofthefollowingsubstanceswasdissolvedin1,000gramsofwater,whichsolutionwouldhavethehighestboilingpoint?

(A)NaCl(B)KCl(C)CaCl2

(D)C6H10O5

(E)C12H22O11

34.Atetrahedralmolecule,XY4,wouldbeformedifXwereusingtheorbitalhybridization

(A)p2(B)s2

(C)sp(D)sp2

(E)sp3

35.Inthefollowingreaction,howmanylitersofSO2atSTPwillresultfromthecompleteburningofpuresulfurin8litersofoxygen?

S(s)+O2(g)→SO2(g)(A)1(B)4(C)8(D)16(E)32

36.Intheabovelaboratorysetuptomeasurethepressureoftheconfinedgas,whatwillbetrueconcerningthecalculatedpressureonthegas?

(A)Thegaspressurewillbethesameastheatmosphericpressure.(B)Thegaspressurewillbelessthantheatmosphericpressure.(C)Thegaspressurewillbegreaterthantheatmosphericpressure.

(D)Thedifferenceintheheight(h)ofmercurylevelsisequaltothepressureofthegas.

(E)Theheight(h)ofmercuryhasnoeffectonthepressurecalculationsincethecolumnofmercuryisonlyusedtoenclosethegasvolume.

37.Whichofthefollowingchangesintheexperimentshowninquestion36wouldcausethepressureintheglasscontainertovaryfromthatshown?

(A)UseaU-tubeofagreaterdiameterandmaintaintheheightofmercury.(B)Increasethetemperatureofgasinthetube.(C)Increasethelengthoftheupperportionoftherightsideoftubing.(D)UseaU-tubeofasmallerdiameterandmaintaintheheightofmercury.(E)Replacetheflaskwithonethathasthesamevolumebuthasaflat

bottom.

38.Whichofthefollowingcanbeclassifiedasamphoteric?

(A)Na3PO4

(B)HCl(C)NaOH(D)HSO4

−

(E)C2O42−

39.Standardconditions(STP)are

(A)0°Cand2atm(B)32°Fand76torr(C)273Kand760mmHg(D)4°Cand7.6cmHg(E)0Kand760mmHg

40.Laboratoryresultsshowedthecompositionofacompoundtobe58.81%barium,13.73%sulfur,and27.46%oxygen.Whatistheempiricalformulaofthecompound?

(A)BaSO4

(B)BaS2O(C)Ba2SO3

(D)BaS2O4

(E)Ba2SO4

41.Whatisthepercentagecompositionofcalciumincalciumhydroxide,Ca(OH)2?(1mol=74g)

(A)40%(B)43%(C)54%(D)69%(E)74%

42.Howmanygramsofhydrogengascanbeproducedfromthefollowingreactionif65gramsofzincand65gramsofHClarepresentinthereaction?

Zn(s)+2HCl(aq)→ZnCl2(aq)+H2(g)

(A)1.0(B)1.8(C)3.6(D)7.0(E)58

43.Thefollowingstatementswererecordedwhilepreparingcarbondioxidegasinthelaboratory.Whichoneinvolvesaninterpretationofthedataratherthananobservation?

(A)Noliquidwastransferedfromthereactionbottletothebeaker.(B)Thequantityofsolidmineralsdecreased.(C)Thecloudinessinthelastbottleoflimewaterwascausedbytheproduct

ofthereactionofthecolorlessgasandthelimewater.(D)Thebubblesofgasrisingfromthemineralremainedcolorless

throughouttheexperiment.(E)Therewasa4°Criseintemperatureinthereactionvesselduringthe

experiment.

44.Theabovelaboratorysetupcanbeusedtopreparewhichofthefollowing?

I.CO2(g)II.H2(g)III.O2(g)

(A)Ionly(B)IIIonly(C)IandIIIonly(D)IIandIIIonly(E)I,II,andIII

45.Themissingproductinthenuclearreactionrepresentedaboveis

46.Whichofthefollowingis(are)trueregardingtheaqueousdissociationofHCN,Ka=4.9×10−10,at25°C?

I.Atequilibrium,[H+]=[CN−].II.Atequilibrium,[H+]>[CN−].III.HCN(aq)isastrongacid.

(A)Ionly

(B)IIonly(C)IandIIonly(D)IandIIIonly(E)I,II,andIII

47.Thisquestionpertainstothereactionrepresentedbythefollowingequation:

2NO(g)+O2(g) 2NO2(g)+150kJ

Supposethat0.8moleofNOisconvertedtoNO2intheabovereaction.Whatamountofheatwillbeevolved?

(A)30kJ(B)60kJ(C)80kJ(D)130kJ(E)150kJ

48.HowdoesaBrønsted-Lowryaciddifferfromitsconjugatebase?

(A)Theacidhasonemoreproton.(B)Theacidhasonelessproton.(C)Theacidhasonemoreelectron.(D)Theacidhasonelesselectron.(E)Theacidhasmorethanoneadditionalproton.

49.Twocontainershaving1moleofhydrogengasand1moleofoxygengas,respectively,areopened.Whatwillbetheratiooftherateofeffusionofthehydrogentothatoftheoxygen?

(A)(B)4:1(C)8:1(D)16:1(E)

50.Amoleculeinwhichtheelectronconfigurationisaresonancehybridis

(A)SO2

(B)C2H6

(C)Cl2(D)HBr(E)NaCl

51.WhatisthepHofasolutioninwhichthe[OH−]is1.0×10−4?

(A)−4(B)+4(C)+7(D)−10(E)+10

52.If0.365gramofhydrogenchlorideisdissolvedtomake1literofsolution(Cl=35.5andH=1.00),thepHofthesolutionis

(A)0.001(B)0.01(C)1(D)2(E)12

53.Inthelaboratory,asampleofhydratedsaltwasheatedat110°Cfor30minutesuntilallthewaterwasdrivenoff.Thedatawereasfollows:

Massofthehydratebeforeheating=250gramsMassofthehydrateafterheating=160gramsFrom these data, what was the percent of water bymass in the originalsample?(A)26.5(B)36(C)47(D)56(E)90

54.Whichofthefollowingoxidesdissolvesinwatertoformanacidicsolution?

(A)Na2O

(B)CaO(C)Al2O3

(D)ZnO(E)SO3

55.Inthelaboratory,20.0millilitersofanaqueoussolutionofcalciumhydroxide,Ca(OH)2,wasusedinatitration.Adropofphenolphthaleinwasaddedtoittoindicatetheendpoint.Thesolutionturnedcolorlessafter20.0millilitersofastandardsolutionof0.050MHClsolutionwasadded.WhatwasthemolarityoftheCa(OH)2?

(A)0.010M(B)0.025M(C)0.50M(D)0.75M(E)1.0M

56.WhichofthefollowingreactionswillNOTspontaneouslygotocompletion?

(A)Zn(s)+2HCl(aq)→ZnCl2(aq)+H2(g)(B)CaCO3(s)+2HCl(aq)→CaCl2(aq)+H2O(aq)+CO2(g)

(C)Ag+(aq)+HCl(aq)→AgCl(s)+H+(aq)(D)Cu(s)+2H+(aq)→Cu2+(aq)+H2(g);E0=−0.34V(E)H2SO4(aq)+2NaOH(aq)→Na2SO4(aq)+2H2O(aq)

57.Foralaboratoryexperiment,astudentplacedsodiumhydroxidecrystalsonawatchglass,assembledthetitrationequipment,andpreparedasolutionof0.10Msulfuricacid.Thenheweighed4gramsofsodiumhydroxideandaddedittoenoughwatertomake1literofsolution.Whatmightbeasourceoferrorintheresultsofthetitration?

(A)Somesulfuricacidevaporated.(B)Thesulfuricacidbecamemoreconcentrated.(C)TheNaOHsolutiongainedweight,thusincreasingitsmolarity.(D)TheNaOHcrystalsgainedH2Oweight,thusmakingthesolutionless

than0.1M.

(E)TheevaporationofsulfuricacidsolutioncounteredtheabsorptionofH2ObytheNaOHsolution.

58.If60.gramsofNOisreactedwithsufficientO2toformNO2thatisremovedduringthereaction,howmanygramsofNO2canbeproduced?(Molarmasses:NO=30.g/mol,NO2=46.g/mol)

(A)46.(B)60.(C)92.(D)120(E)180

59.Basedontheinformationshown,eachofthefollowingequationsrepresentsareactioninwhichthechangeinentropy, S,ispositiveEXCEPT

(A)CaCO3(s)→CaO(s)+CO2(g)

(B)Zn(s)+2H+(aq)→H2(g)+Zn2+(aq)(C)2C2H6(g)+7O2(g)→4CO2(g)+6H2O(g)

(D)NaCl(s)→Na+(aq)+Cl−(aq)(E)N2(g)+3H2(g)→2NH3(g)

60.Cl2(g)+2Br−(excess)→?

When1moleofchlorinegasreactscompletelywithexcessKBrsolution,asshownabove,theproductsobtainedare(A)1molofCl−ionsand1molofBr−

(B)1molofCl−ionsand2molofBr−

(C)1molofCl−ionsand1molofBr2(D)2molofCl−ionsand1molofBr2(E)2molofCl−ionsand2molofBr2

61.Twowatersolutionsaremadeinthelaboratory,oneofglucose(molarmass=180g/mol),theotherofsucrose(molarmass=342g/mol).Iftheglucosesolutionhad180gramsin1,000gramsofwaterandthesucrosehad342gramsin1,000gramsofwater,whichstatementaboutthefreezingpointsofthesolutionsisthemostaccurate?

(A)Theglucosesolutionwouldhavethelowerfreezingpoint.(B)Thesucrosesolutionwouldhavethelowerfreezingpoint.(C)Thefreezingpointofthesucrosesolutionwouldbeloweredtwiceas

muchasthatoftheglucosesolution.(D)Bothsolutionswouldhavethesamefreezingpoint.(E)Thefreezingpointsofthesolutionswouldnotbeaffected,becauseboth

solutesarenonpolar.

62.WhichKavalueindicatesthestrongestacid?

(A)1.3×10−2

(B)6.7×10−5

(C)5.7×10−10

(D)4.4×10−7

(E)1.8×10−16

63.WhatmassofCaCO3isneededtoproduce11.2litersofCO2atSTPwhenthecalciumcarbonateisreactedwithanexcessamountofhydrochloricacid?(Molarmasses:CaCO3=100.g/mol,HCl=36.5g/mol,CO2=44.0g/mol)

(A)25.0g(B)44.0g(C)50.0g(D)100.g(E)Noneoftheabove

64.ByexperimentationitisfoundthatasaturatedsolutionofBaSO4at25°Ccontains3.9×10−5mole/literofBa2+ions.WhatistheKspoftheBaSO4?

(A)1.5×10−4

(B)1.5×10−9

(C)1.5×10−10

(D)3.9×10−10

(E)39×10−9

65.Whatisthe H°valueforthedecompositionofsodiumchlorate,giventhe

followinginformation?

NaClO3(s)→NaCl(s)+ O2(g)

( H°fvalues:NaClO3(s)=−358J/mol,NaCl(s)=−410J/mol,O2(g)=0kcal/mol)

(A)52.0J(B)−52.0J(C)768J(D)−768J(E) (768J)

66.Totheequilibriumreactionshownbelow:

AgCl(s) Ag++Cl−

a beaker of concentratedHCl (12M) is slowly added.Which is the bestdescriptionofwhatwilloccur?

(A)Moresaltwillgointosolution,andtheKspwillremainthesame.(B)Moresaltwillgointosolution,andtheKspwillincrease.(C)Saltwillcomeoutofthesolution,andtheKspwillremainthesame.(D)Saltwillcomeoutofthesolution,andtheKspwilldecrease.(E)Nochangeinconcentrationwilloccur,andtheKspwillincrease.

67.Whenthefollowingredoxequationisbalancedandallcoefficientsarereducedtolowestwhole-numberterms,whatisthecoefficientofH2O?

HCl+KMnO4→H2O+KCl+MnCl2+Cl2(A)1(B)2(C)5(D)8(E)16

68.Eachofthefollowingsystemsisatequilibriuminaclosedcontainer.Adecreaseinthetotalvolumeofeachcontainerwillincreasethenumberofmolesofproduct(s)forwhichsystem?

(A)2NH3(g) N2(g)+3H2(g)(B)H2(g)+Cl2(g) 2HCl(g)(C)2NO(g)+O2(g) 2NO2(g)(D)CO(g)+H2O(g) CO2(g)+H2(g)(E)Fe3O4(s)+4H2(g) 3Fe(s)+4H2O(g)

69.WhichofthefollowingisthecorrectandcompleteLewiselectron-dotdiagramforPF3?

70.Hydrogengasiscollectedinaeudiometertubeoverwaterasshownabove.Thewaterlevelinsidethetubeis40.8millimetershigherthanthatoutside.Thebarometricpressureis730.millimetersHg.Thewatervaporpressureattheroomtemperatureof29°Cisfoundinahandbooktobe30.0millimetersHg.Whatisthepressureofthedryhydrogen?

(A)659.2mmHg

(B)689.2mmHg(C)697.0mmHg(D)740.8mmHg(E)800.8mmHg

71.Howmanymolesofelectronsarerequiredtoreduce2.93gramsofnickelionsfrommeltedNiCl2?(MolarmassofNi=58.7g/mol)

(A)0.050(B)0.10(C)1.0(D)1.5(E)2.0

Ifyoufinishbeforeonehourisup,youmaygobacktocheckyourworkorcompleteunansweredquestions.

AnswerKeyDIAGNOSTICTEST

1.A 14.D 102.T,T,CE2.A 15.E 103.T,F3.E 16.B 104.F,T4.D 17.B 105.F,F5.E 18.A 106.T,T,CE6.A 19.B 107.F,F7.D 20.E 108.F,T8.D 21.C 109.F,T

9.E 22.B 110.T,T,CE10.C 23.C 111.T,T,CE11.A 24.E 112.T,T12.B 25.C 113.T,F13.C 101.T,T,CE 114.T,F

26.E 41.C 56.D27.D 42.B 57.D28.B 43.C 58.C29.A 44.E 59.E30.D 45.C 60.D31.D 46.A 61.D32.D 47.B 62.A33.C 48.A 63.C34.E 49.B 64.B35.C 50.A 65.B36.C 51.E 66.C37.B 52.D 67.D38.D 53.B 68.C39.C 54.E 69.E40.A 55.B 70.C

71.B

ANSWERSEXPLAINED1.(A)Inthehalogenfamily,themostactivenonmetalwouldbethetopelement,fluorine,becauseithasthehighestelectronegativity.

2.(A)Asyouproceeddownagroup,theionicradiusincreasesasadditionalenergylevelsarefilledfartherfromthenucleus.Thereforefluorine,thetopelement,hasthesmallestionicradius.

3.(E)Sinceastatinehasthelargestatomicradiusanditsouterelectronsareshieldedfromtheprotonsbyalargenumberofinteriorelectrons,ithasthelowestfirstionizationpotential.

4.(D)Somephysicalcharacteristicsofmetalarefoundiniodine,thefourthhalogendowninthegroup.

5.(E)The3dsubshellhas5orbitals,or5possiblevaluesofm(−2,−1,0,+1,and+2).ThePauliexclusionprincipleallowseachorbitalamaximumof2electronswithoppositespins.Sothe3dsubshellcancontainupto10electrons.

6.(A)Thegroundstateisthelowest-energy,ormoststablestate,ofanatom.Thelithiumatomhas3electrons.Initsstablestate,the1ssubshell,orlowest-energyorbital,containsapairofelectrons.ThePauliexclusionprincipleallowsamaximumof2electronswithoppositespins,sothethirdelectronresidesinthe2sorbital.

7.(D)Phosphorushas15electrons.Initsmoststablestate,thelowest-energysubshellswillbeoccupied.Oneelectronfillstheorbitalofasubshellbeforecouplinginelectronspinpairsbegins.Forphosphorus,12electronsfillthe1s2,2s2,2p6,and3s2orbitals.Theremaining3electronsfillexactlyone-halfofthe3porbitals,withallofthespinsinthesamedirection,or3p3.

8.(D)JohnDaltoniscreditedwiththebasicpostulatesofatomictheory.

9.(E)Gay-Lussaciscreditedwiththestatementthat,whengasescombine,theydosoinratiosofsmallwholenumbersthatareinrelationshiptothevolumesofthereactantsandthevolumesoftheproductsunderthesameconditions.

10.(C)Charlesiscreditedwiththistemperature-volumerelationshipofgases:

orV1T2=V2T1asshowninthequestion.

11.(A)Avogadroiscreditedwiththeconceptregardingthenumberofparticlesinamole,6.02×1023,andthisnumberbearshisname.

12.(B)BoyleiscreditedwiththeP1V1=P2V2relationshipofgases.

13.(C)Thisincludesthefunctionalgroupofanaldehyde.

14.(D)Thisincludesthefunctionalgroupofanorganicacid.

15.(E)Anesteristheequivalentofanorganicsaltsinceitisusuallyformedfromanorganicalcohol,

R–OH,plusanorganicacid, .

Thebondingis ,whichgives

.(R*indicatesthatthishydrogenbranchneednotbethesameasR.)

16.(B)Thisincludesthefunctionalgroupofanether.Itcanbeformedbythedehydrationoftwoalcoholmolecules.Thereactionis

17.(B)ThemolecularstructureofcarbondioxideisO=C=O,wheretheoxygensare180°apartand,althoughthebondingispolartothecarbon,counteracteachothertoconstituteanonpolarmolecule.

18.(A)Ahydrogengasmoleculeisdiatomic;ithas2molofatomsineachmoleofmolecules,representedbyH2.

19.(B)EachCO2hasthreeatomspermolecule;hencetheexpressioncanrepresent3molofatomsin1molofmolecules.

20.(E)Withcompleteionization ,or3molofionspermoleofH2SO4.

21.(C)Theexpression2N2Orepresentstwotriatomicmoleculesor6molofatoms.

22.(B)The16Oand17Oareisotopesofthesameelementbecausetheydonothavethesamenumberofneutrons.Thisdifferenceinthenumberofneutronsshowsupinthemassnumber(superscripttotheleftofthechemicalsymbol).Themassofanelementisthesumoftheprotonsandneutronsinthenucleus.

23.(C)InNH4Cl,thecovalentlybondedNH4+ionisionicallybondedtotheCl

−ion.InNH4NO3,thecovalentlybondedNH4+ionisionicallybondedto

thecovalentlybondedNO3−ion.Ineachofthesecationsandanionsare

covalentbondswithinthestructurewheretheelectronsaresharedequally.

24.(E)TheO2andO3areallotropesbecausetheyaredifferentmolecularformsofthesameelementinthesamestate.Theyhavedifferentstructuresduetodifferentbondarrangements.

25.(C)Strongelectrolyteswillalmostcompletelydissociateinaqueoussolutions.BothNH4ClandNH4NO3areioniccompoundsthatdissociatetoreleasetheammoniumcationandeithertheCl−ortheNO3

−anion.

101.(T,T,CE)Acatalystcanaccelerateachemicalreactionbyloweringtheactivationenergyrequiredforthereactiontooccur.

102.(T,T,CE)Sodiumchlorideisanionicsubstanceandwhenmoltenisagoodelectricalconductor,andthereasonisthatinthemoltenstatetheionsarefreetomigratetotheanodeandcathode.

103.(T,F)Iceislessdensethanliquidwater.Watermolecules,however,arepolar,notnonpolar,andwaterexpandsasthesemoleculesarrangethemselvesintoacrystallattice.

104.(F,T)Thestatementthatisotopesofthesameelementhavethesamemassnumberisfalse.Isotopesofthesameelementhavethesamenumberofprotonsbutvaryinthenumberofneutronsinthenucleus.Therefore,theseisotopeshavethesameatomicnumberbutdifferentmassnumbers.

105.(F,F)TherearefewerCaatomsin1moleofcalciumcarbonate(CaCO3)thanin1moleofcalciumcitrate(Ca3(C6H5O7)2)becauseeachmoleofcalciumcitratecontains3timesmoreCathaneachmoleofcalciumcarbonate.

106.(T,T,CE)Thereactionis:

C+O2→CO2

andshows1molor12.0gofcarbonproduces1molor22.4LofCO2.Then

Sothestatementiscorrect,andtheassertionexplainsitcorrectly.

107.(F,F)Areactionatequilibriumhasreachedapointwheretheforwardandreversereactionsareoccurringatequalrates.Theconcentrationsofthereactantsandproducts,however,arenotnecessarilyequalandaredescribedbytheKeqvalueatthetemperatureofthereaction.

108.(F,T)Inanelectrolytereaction,anionsmigratetotheanode.Itistruethatpositivelychargedions(cations)areattractedtothenegativelychargedcathode.

109.(F,T)ThevaluepH=5canbeexpressedas

andpH=3as

ThuspH=3representsalargerconcentrationofhydroniumions,H3O+.

110.(T,T,CE)Thefirststatementistrue.ThechangeinGibbsfreeenergy, G,dependsontheenthalpychange, H,andtheentropychange, S,fromtheequation G= H-T S.Thus,statementIIisalsotrueandexplainsthefirststatement.

111.(T,T,CE)Intheexpressionfortheequilibriumconstantofanacid,[H3O+]isinthenumerator:

As[H3O+]decreasesintheweakacids,thenumeratorbecomessmallerasthedenominatorgetslarger,thereforegivingsmallerKavalues.

112.(T,T)Bothstatementsaretrue,buttheyarenotrelated.

113.(T,F)Apibondisformedbetweenplobesofadjacentatomsandinthesameplane:

However,eachporbitalconsistingoftwolobescanholdatotaloftwoelectrons,sothereasonisfalse.

114.(T,F)TheassertionthattheboilingpointsofH2SandH2Oaresignificantlydifferentistrue,butthereasonisfalse.Waterhasthehigherdegreeofhydrogenbonding.

26.(E)Twoimmiscibleliquids,whenshakentogethervigorously,mayeachformsmall,colloidal-sizeparticles,dispersedintheotherliquid.

27.(D)Inthegraph,thefirstplateaumustrepresentthecondensationfromgastoliquidbecausethereisasecond,lowerplateau,whichwouldrepresentthesecondchangeofstate,fromliquidtosolid.

28.(B)Iftheelectronshavethesameprincipalenergylevel,theywillfillthes2,p6,thenthed10level.Thisprogressionisfromthelowestenergysubleveltothehighest,toaccommodate18electrons.

29.(A)Whenthechainorringcarriesthefullcomplementofhydrogenatoms,thehydrocarbonissaidtobesaturated.ThegeneralformulaforthesaturatedalkanesisCnH2n+2.ThechainisCH3−CH2−CH3.

30.(D)ConsideringtheconceptsbehindCharles’sLawandBoyle’sLaw,youcanarriveatthefractiontobeusedinkelvinsandtorrs.Thevolumemustincreasewithanincreaseintemperatureandalsoincreasewithadecreasein

pressure.Thereforethefractionswouldbe and

Usingthecombinedgaslawequation,

andsolvingforV2,youget

whichisthesameanswer.

31.(D)Themassnumber,32,isthetotalnumberofneutronsandprotons.Sincetheatomicnumber,16,givesthenumberofprotons,32−16=16,orthenumberofneutrons,statementIIisfalse.Sincethisionhasachargeof2−,ithastwomoreelectronsthanprotons,or18electrons.StatementsIandIIIaretrue.

32.(D)ThemostactivemetallicelementsarefoundinthelowerleftcornerofthePeriodicTable.

33.(C)Theriseintheboilingpointdependsonthenumberofparticlesinsolution.OnemoleofCaCl2gives3molofions,morethananyothersubstancelisted:

CaCl2→Ca2++2Cl−.

Thenumberofmolesofionsgivenbytheothersubstancesareasfollows:

(A)=2,(B)=2,(D)=1,(E)=1.

34.(E)Thesp3hybridhasthetetrahedronconfiguration.Thesp2(D)istrigonalplanar.Thesp(C)islinear.Thes(B)andp(A)aretheusualorbitalstructures.

35.(C)Thereactionis

Thegiven(8L)andtheunknown(xL)areshownabove.Sincetheequation,accordingtoGay-Lussac’sLaw,showsthat1volumeofoxygenyields1volumeofsulfurdioxide,then

36.(C)ThefactthatthemercurylevelintheU-tubeishigherintherightsideofthetubeindicatesthatthepressureintheflaskishigherthantheatmosphericpressureexertedontheopenendofthetubeontherightside.Ifthepressureinsidetheflaskwerethesameastheatmosphericpressure,theheightofthemercurywouldbethesameinbothsidesoftheU-tube.

37.(B)Theonlychangelistedthatwouldchangethepressureofthegasinsidetheflaskistoincreasethetemperatureofthegas.Thiswouldcausethepressuretorise.

38.(D)Anamphotericsubstancemustbeabletobeaproton,(H+),donor,andaprotonreceiver.Thebisulfateion,HSO4

−,istheonlychoicethatcaneitheracceptaprotonandbecomeH2SO4,orloseaprotonandbecomethesulfateion,SO4

2−.

39.(C)Standardconditionsare273Kand760mmHg.

40.(A)Dividingthepercentageofeachelementbytheatomicmassofthatelementgivesthebasicratioofatoms,butnotnecessarilyinwholenumbers.Thus,(Ba)58.8÷137=0.43,(S)13.7÷32=0.43,(O)27.5÷16=1.72.

Because atoms occur inwhole numbers, you nowmustmanipulate thesenumbers mathematically to get whole numbers. Usually dividing eachnumberbythesmallestonehelpstoaccomplishthis:(Ba)0.43÷0.43=1,(S)0.43÷0.43=1,(O)1.72÷0.43=4.TheempiricalformulaisBaSO4.

41.(C)Thepercentagecompositioncanbefoundbydividingeachtotalatomicmassintheformulabythemolarmassofthecompound.

CA=4040÷74×100%=54%Ca2O=3232÷74×100%=43%O2H= 2÷74×100%=2.7%H

42.(B)Thesolutionsetupis:

Notethattheequationmassiscalculatedunderthesubstancesthathavemassunitsabovethem.Accordingtothecalculatedequationmasses,73gofHClwouldbeneededtoreactwith65gofzinc.Sincethereisonly65gofHCl,weusethisanddisregardthe65gofZn.

=1.78or1.8gofH2

43.(C)Alltheotherstatementsrepresentobservationsbecausetheymerelyrecordwhatwasseen.

44.(E)Thesetupisappropriateforthecollectionofabasicallynonsolublegasbythedisplacementofwater.Allthreegasesfitthisdescription.

45.(C)Withtheemissionofaneutron,thetotalatomicmassdecreasesby1.However,thenumberofprotonsis2.Theproductishelium,

46.(A)ThesmallKaindicatesthatthisisaweakacid,sostatementIIIisfalse.WhenHCNionizes,itcanbeshownthatHCN H++CN−.Thisisamolarratioof1:1,sostatementImustbetrue.

47.(B)Becausetheequationshowsthat2molofNOreacttorelease150kJ,thesolutionis

Thisproblemwouldbesolvedinthesamemanneriftheheathadbeenexpresssedinkilocalories.Toconvertoneunittotheother,use4.18×103J=1kcal.

48.(A)IntheBrønsted-Lowryacid-basetheory:

49.(B)AccordingtoGraham’sLaw,theratesofeffusionoftwogasesareinverselyproportionaltothesquarerootsoftheirmolarmasses.Since1molO2=32gand1molH2=2g

Therefore,theeffusionrateofhydrogenisfourtimesfasterthanthatofoxygen.

50.(A)ThestructureofSO2isaresonancehybrid,shownastheseresonancestructures:

51.(E)TheKwofwateris

Kw=[H+][OH−]=10−14

If[OH−]=1.0×10−4,then

andpH=−log[H+]=10

52.(D)

0.01molHCl→0.01molH++0.01molCl−

If[H+]=0.01=1×10−2mol/L,thenpH=2.

53.(B)Hydratemassbeforeheating=250.g

-Hydratemassafterheating=160.gWaterloss=90.0g

54.(E)Becausemetallicoxidesarebasicanhydrides,theonlynonmetallicoxideisSO3.Thereactionisasfollows

SO3+H2O→H2SO4(sulfuricacid)

55.(B)Inthetitration,thereactionis:

2HCl+Ca(OH)2→CaCl2+2H2O

Theacidtobaseratiois2:1,or(molesacidused)=2(molesbaseused),soMaVa=2MbVb,whereMisthemolarityandVisthevolumeexpressedinliters,then

56.(D)Allthereactionswillgotocompletionexcept(D),whichwillnotoccurspontaneouslyatall.IfE0hadbeenpositive,however,thisredoxreactionwouldoccur.

57.(D)Sodiumhydroxideishygroscopicandwillattractwatertoitssurfacearea.Thiswaterwillinfluenceitsmass;consequentlytherewillbelesssodiumhydroxideinthemassused.

58.(C)

This is a mass stoichiometry problem. The equation masses are placedbeneaththesubstancesthathavequantitiesabovethem.

Usingtheequationrelationshipgives

Usingthemolemethodgives

Usingtheequationcoefficientsgives

then

59.(E)Sinceinthisreaction4volumesofgasesareforming2volumesofproduct,therandomnessofthesystemisdecreasing.Therefore,entropyisdecreasingand Sisnegative.Inalltheotherreactionsrandomnessisincreasing.

60.(D)Thereactionis

Cl2(g)+2Br−(excess)→2Cl−+Br2(g)

Here2molofchlorideionsand1molofBr2moleculesareproduced.

61.(D)Sincebothsolutionswere1molalandneithercompoundionizedintomoreparticles,thefreezingpointswouldbethesame.

62.(A)HY H++Y−

Since[H+]isinthenumeratorofKa:

Thestrongertheacid,thegreaterare[H+]andtheKavalue.Ofthechoicesgiven,1.3×10−2isthelargest.

63.(C)

Thisisamass-volumeproblemwiththemassandvolumeindicatedbelowtheequation.Usingthefactor-labelmethodgives

Usingthemolemethodgives

64.(B)Ksp=[Ba2+][SO42−]

If[Ba2+]=3.9×10−5,then[SO42−]mustalsoequalthesameamount,so

Ksp=[3.9×10−5][3.9×10−5]

=15.2×10−10or1.5×10−9.

65.(B) H0reaction= H0

f(products)− H0f(reactants)

H0reaction=−410.J−(−358.J)

H0reaction=−52.J

66.(C)BecausetheHClsolutionwilladdtothechlorideionconcentration,accordingtoLeChâtelier’sPrincipletheequilibriumwillshiftinthedirectiontoreducethisdisturbance,sotheKspwillremainthesamebutsaltwillcomeoutofsolution.Thisprocess:

AgCl Ag++Cl−

willcontinueuntil theKspisreestablished.Thisphenomenoniscalledthe“commonioneffect.”

67.(D)HCl+KMnO4→H2O+KCl+MnCl2+Cl2oxidation:2Cl−→Cl2+2e−

reduction:8H++MnO4−+5e−→Mn2++4H2O

5(oxidationreaction)and2(reductionreaction)willbalancethee−gainandloss,giving10Cl−→5Cl2+ e−

16H++2MnO4−+ e−→2Mn2++8H2O

Therefore16HCl+2KMnO4→8H2O+2KCl+2MnCl2+5Cl2

68.(C)Adecreaseinvolumewillcausetheequilibriumtoshiftinthedirectionthathaslessvolume(s)ofgas(es).Ineverycaseexcept(C)thisisthereversereaction,whichdecreasestheproduct.Thecoefficientsgivethevolumerelationships.

69.(E)ThecentralPhas5valenceelectrons.Ofthese,2arepaired.Theremaining3valenceelectronseachcovalentlybondwithoneofthe3Ftofilltheouterenergylevel.TheLewiselectron-dotdiagramis

70.(C)ChangethewaterheighttotheequivalentHgheight:

=3mmHg

Adjustforthedifferenceinheighttogetthegaspressure.Pressureonthegasis

730.mmHg−3mmHg=727mmHg.

VaporpressureofH2Oat29°Caccountsfor30mmHgpressure.Therefore

727mmHg−30mmHg=697mmHg

71.(B)Thereactionis

Ni2++2e−→Ni(s)Since2molofelectronsarerequiredtoform1molofnickel,and

then

=0.1molofelectrons

CALCULATINGYOURSCOREYourscoreonthediagnostictestcannowbecomputedmanually.Theactualtestwill be scored bymachine, but the samemethod is used to arrive at the rawscore.Yougetonepoint foreachcorrectanswer.Foreachwronganswer,youlose one-fourth of a point. Questions that you omit or for which you haveindicatedmorethanoneanswerarenotcounted.Onyouranswersheet,markallcorrectanswerswitha“C”andallincorrectanswerswithan“X.”

DeterminingYourRawTestScoreTotalthenumberofcorrectanswersyouhaverecordedonyouranswersheet.ItshouldbethesameasthetotalofallthenumbersyouplaceintheblockinthelowerleftcornerofeachareaoftheSubjectAreasummaryinthenextsection.

A.Enterthetotalnumberofcorrectanswershere:________Nowcountthenumberofwronganswersyourecordedonyouranswersheet.

B.Enterthetotalnumberofwronganswershere:________MultiplythenumberofwronganswersinBby0.25.

C.Enterthatproducthere:________SubtracttheresultinCfromthetotalnumberofrightanswersinA.

D.Entertheresultofyoursubtractionhere:________E.RoundtheresultinDtothenearestwholenumber:________.

Thisisyourrawtestscore.

ConversionofRawScorestoScaledScoresYour raw score is converted by the College Board into a scaled score. TheCollegeBoardscoresrangefrom200to800.ThisconversionisdonetoensurethatascoreearnedonanyeditionofaparticularSATSubjectTestinChemistryiscomparabletothesamescaledscoreearnedonanyothereditionofthesametest.Becausesomeeditionsofthetestsmaybeslightlyeasierormoredifficultthan others, scaled scores are adjusted so that they indicate the same level ofperformance regardless of the edition of the test taken and the ability of thegroup that takes it. Consequently, a specific raw score on one edition of aparticulartestwillnotnecessarilytranslatetothesamescaledscoreonanothereditionofthesametest.

Since thepractice tests in thisbookhaveno largepopulationofscoreswithwhichtheycanbescaled,scaledscorescanonlybeapproximated.Results from previous SAT Chemistry tests appear to indicate that the

conversionofrawscorestoscaledscoresGENERALLYfollowsthispattern:

Note that this scale provides only a general idea of what a raw score maytranslateintoonascaledscorerangeof800–200.Scalingoneverytestisusuallyslightly different. Some students who have taken the SAT Subject Test inChemistry after using this book have reported that they have scored slightlyhigherontheSATtestthanonthepracticetestsinthisbook.Theyallreportedthatpreparingwellforthetestpaidoffinabetterscore!

DIAGNOSINGYOURNEEDSThissectionwillhelpyoutodiagnoseyourneedtoreviewthevariouscategoriestestedbytheSATSubjectTestinChemistry.Aftertakingthediagnostictest,checkyouranswersagainstthecorrectones.

Then fill in thechartbelow. In the spaceundereachquestionnumber,placeacheck( )ifyouansweredthatquestioncorrectly.Next,totalthechecksforeachsectionandinsertthenumberinthedesignated

block.Nowdothearithmeticindicated,andinsertyourpercentageforeacharea.

PLANNINGYOURSTUDYThepercentagesgiveyouan ideaofhowyouhavedoneon thevariousmajorareasofthetest.Becauseofthelimitednumberofquestionsonsomeparts,thesepercentages may not be as reliable as the percentages for parts with largernumbersofquestions.However,youshouldnowhaveatleastaroughideaoftheareas inwhich you have donewell and those inwhich you needmore study.(Therearefourmorepracticetestsinthebackofthisbook,whichmaybeusedinadiagnosticmanneraswell.)Start your study with the areas in which you are the weakest. The

correspondingchaptersareindicatedonthenextpage.

Afteryouhavespentsometimereviewingyourweakerareas,planascheduleofworkthatspansthe6weeksbeforethetest.Unlessyousetuparegularstudypatternandgoals,youprobablywillnotpreparesufficiently.Thefollowingscheduleprovidessuchaplan.Notethatweekendsareleftfree,

andthetimespansareheldto1-or2-hourblocks.Thiswillbetimewellspent!

FINALPREPARATION—THEDAYBEFORETHE

TESTThedaybeforethetest,reviewoneofthepracticetestsyouhavealreadytaken.Studyagainthedirectionsforeachtypeofquestion.Longhoursofstudyatthispoint will probably only heighten your anxiety, so just look over the answersectionofthepracticetestandrefertoanychapterinthebookifyouneedmoreinformation.This type of limited, relaxed reviewwill probablymakeyou feelmorecomfortableandbetterprepared.Gettogetherthematerialsthatyouwillneed.Theyare:

•Youradmissionticket.Checkthetimeyouradmissionticketspecifiesforarrival.

•Youridentification.(YouwillnotbeadmittedwithoutsometypeofpositiveidentificationsuchasastudentI.D.cardwithpictureoradriver’slicense.)

•TwoNo.2pencilswitherasers.

•Watch(withoutanaudiblealarm)

Cellphoneuse isprohibited inboth the test center and the testing room! Ifyourcellphoneison,yourscoreswillbecanceled!

NotethatcalculatoruseisnotallowedduringtheSATSubjectTestinChemistry.Youshouldalsogooverthischecklist:

A.Planyouractivitiessothatyouwillhavetimeforagoodnight’ssleep.

B.Layoutcomfortableclothesforthenextday.Youmaywanttobringasnack.

C.Reviewthefollowinghelpfultipsabouttakingthetest:

1.Readthedirectionscarefully.2.Ineachgroupofquestions,answerfirstthosethatyouknow.Temporarilyskipdifficultquestions,butmarktheminthemarginsoyoucangobackifyouhavetime.Keepinmindthataneasyquestionansweredcorrectlycountsasmuchasadifficultone.

3.Avoidhaphazardguessingsincethiswillprobablyloweryourscore.Instead,guesssmart!Ifyoucaneliminateoneormoreofthechoicestoaquestion,itwillgenerallybetoyouradvantagetoguesswhichofthe

remaininganswersiscorrect.Yourscorewillbebasedonthenumberrightminusafractionofthenumberansweredincorrectly.

4.Omitquestionswhenyouhavenoideaofhowtoanswerthem.Youneithergainnorlosecreditforquestionsyoudonotanswer.

5.Keepinmindthatyouhave1hourtocompletethetest,andpaceyourselfaccordingly.Ifyoufinishearly,gobacktoquestionsyouskipped.

6.Marktheanswergridclearlyandcorrectly.Besureeachanswerisplacedintheproperspaceandwithintheoval.Eraseallstraymarkscompletely.

7.Writeasmuchasyoulikeinthetestbooklet.Useitasascratchpad.Onlytheanswersontheanswersheetarescoredforcredit.

D.Setyouralarmclocksoastoallowplentyoftimetodress,eatyourusual(orevenabetter)breakfast,andreachthetestcenterwithouthasteoranxiety.

AFTERTHETESTAfter several weeks, most scores will be reported online atwww.collegeboard.org.Afullreportwillbeavailable toyouonlineafewdayslater.Youcanrequestapaperreport.Yourscorewillalsobemailedtoyourhighschool and to the colleges, universities, and programs that you indicated. Thereport includes your scores, percentiles, and interpretive information.You canalsogetyourscores—forafee—bytelephone.Callcustomerserviceat866-756-7346intheUnitedStates.FromoutsidetheUnitedStates,call212-713-7789.If your scores are not reported by eightweeks after the test date, definitely

contact customer service by telephone or e-mail (sat@info.collegeboard.org).Themailingaddressforcommentsorquestionsaboutthetestsis:

TheCollegeBoardSATProgramP.O.Box025505Miami,FL33102

PART2

REVIEWOFMAJORTOPICS

CHAPTER1

IntroductiontoChemistry

TheseskillsareusuallytestedontheSATSubjectTestinChemistry.Youshouldbeableto…•Distinguishtypesofmatter:i.e.,elements,mixtures,compounds,anddistinctivesubstances.

•Identifychemicalandphysicalpropertiesandchanges.•Explainhowenergyisinvolvedinthesechanges.•IdentifyandusetheSIunitsofmeasurements.•Domathematicalcalculationsbyusingscientificnotation,thefactor-labelmethod,andpropersignificantfigures.

This chapter will review and strengthen these skills. Be sure to do thePracticeExercisesattheendofthechapter.

MATTERMatter is defined as anything that occupies space and hasmass.Mass is thequantity of matter which a substance possesses and, depending on thegravitationalforceactingonit,hasaunitofweightassignedtoit.Itsformulaisw=mg.Althoughtheweightthencanvary,themassofthebodyisaconstantand canbemeasuredby its resistance to a changeofpositionormotion.Thispropertyofmasstoresistachangeofpositionormotioniscalledinertia.Sincematterdoesoccupyspace,wecancomparethemassesofvarioussubstancesthatoccupyaparticularunitvolume.This relationshipofmass toaunitvolume iscalledthedensityofthesubstance.Itcanbeshowninamathematicalformulaas . The basic unit of mass (m) in chemistry is the gram (g), and of

volume(V)isthecubiccentimeter(cm3)ormilliliter(mL).

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Matteroccupiesspaceandhasmass.

An example of how density varies can be shown by the difference in thevolumesoccupiedby1gramofametal,suchasgold,and1gramofStyrofoam.Bothhavethesamemass,1gram,butthevolumeoccupiedbytheStyrofoamismuchlarger.Therefore,thedensityofthemetalwillbemuchlargerthanthatofthe Styrofoam. In chemistry, the standard units for density of gases aregrams/literatastandardtemperatureandpressure.Thisaspectofthedensityofgases is discussed inChapter 6. Basically then, density can be defined as themassperunitvolume.

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Density=

StatesofMatterMatteroccurs in threestates:solid, liquid,andgas.Asolidhasbothadefinitesizeandadefiniteshape.Aliquidhasadefinitevolumebuttakestheshapeofthecontainer,andagashasneitheradefiniteshapenoradefinitevolume.Thesestates of matter can often be changed by the addition or subtraction of heatenergy.Anexampleisicechangingtoliquidwaterandfinallysteam.

CompositionofMatterMatter can be subdivided into two general categories: distinct substances andmixtures.Adistinctsubstancecanbesubdividedintothesmallestparticlethatstillhasthepropertiesofthatsubstance.Atthatpoint,ifthesubstanceismadeupofonlyonekindofatom,itiscalledanelement.Atomsareconsideredtobethebasicbuildingblocksofmatter thatcannotbeeasilycreatednordestroyed.ThewordatomcomesfromtheGreeksandmeansthesmallestpossiblepieceofsomething. Today, scientists recognize approximately 109 different kinds ofatoms,eachwithitsownuniquecomposition.Theseatomsthenarethebuildingblocks of elements when only one kind of atom makes up the substance. If,however, twoormorekindsofatoms join together inadefinitegrouping, this

distinct substance is called a compound.Compounds aremade by combiningatoms of two or more elements in a definite proportion (or ratio) by mass,accordingtotheLawofDefiniteComposition(orProportions).Thesmallestnaturallyoccurringunitofacompoundiscalledamoleculeofthatcompound.Amolecule of a compound has a definite shape that is determined by how theatomsarebondedtoorcombinedwitheachother,asdescribedinChapter3.Anexample is the compoundwater: it always occurs in a twohydrogen atoms toone oxygen atom relationship. Mixtures, however, can vary in theircomposition.

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Know how to separatemixtures byusingtheirproperties.

Ingeneral,then:

Thefollowingchartshowsaclassificationschemeformatter.

ChemicalandPhysicalPropertiesPhysicalpropertiesofmatterarethosepropertiesthatcanusuallybeobservedwith our senses. They include everything about a substance that can be notedwhennochangeisoccurringinthetypeofstructurethatmakesupitssmallestcomponent.Somecommonexamplesarephysicalstate,color,odor,solubilityinwater,density,meltingpoint,taste,boilingpoint,andhardness.Chemicalpropertiesare those properties that can be observed in regard to

whetherornotasubstancechangeschemically,oftenasaresultofreactingwithothersubstances.Somecommonexamplesare: ironrusts inmoistair,nitrogendoesnotburn,golddoesnotrust,sodiumreactswithwater,silverdoesnotreactwithwater,andwatercanbedecomposedbyanelectriccurrent.

ChemicalandPhysicalChangesThechangesmatter undergoes are classified as either physical or chemical. Ingeneral, a physical change alters some aspect of the physical properties ofmatter,butthecompositionremainsconstant.Themostoftenalteredpropertiesare form and state. Some examples of physical changes are breaking glass,cuttingwood,meltingice,andmagnetizingapieceofmetal.Insomecases,theprocessthatcausedthechangecanbeeasilyreversedandthesubstanceregainsitsoriginalform.Waterchangingitsstateisagoodexampleofphysicalchanges.In the solid state, ice,waterhasadefinite sizeandshape.Asheat isadded, it

changestotheliquidstate,whereithasadefinitevolumebuttakestheshapeofthecontainer.Whenwaterisheatedaboveitsboilingpoint,itchangestosteam.Steam,agas,hasneitheradefinitesize,becauseitfillsthecontainingspace,norshape,becauseittakestheshapeofthecontainer.

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Physical change does not alter theidentity of the substance. Chemicalchangedoes.

Chemical changes are changes in the composition and structure of asubstance. They are always accompanied by energy changes. If the energyreleasedintheformationofanewstructureexceedsthechemicalenergyintheoriginalsubstances,energywillbegivenoff,usuallyintheformofheatorlightorboth.This is calledanexothermicreaction. If, however, thenewstructureneedstoabsorbmoreenergythanisavailablefromthereactants,theresultisanendothermicreaction.Thiscanbeshowngraphically.Notice that in Figures 1 and 2 the term activation energy is used. The

activationenergyistheenergynecessarytogetthereactiongoingbyincreasingthe energy of the reactants so they can combine.You know you have to heatpaper before it burns. This heat raises the energy of the reactants so that theburningcanbegin;thenenoughenergyisgivenofffromtheburningsothatanexternalsourceofenergyisnolongernecessary.

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Knowhowtoreadthesegraphicrepresentations.

Figure1.AnExothermicReaction

Figure2.AnEndothermicReaction

ConservationofMassWhen ordinary chemical changes occur, the mass of the reactants equals themass of the products. This can be stated another way: In a chemical change,mattercanneitherbecreatednordestroyed,butonlychangedfromoneformtoanother.ThisisreferredtoastheLawofConservationofMatter(Lavoisier—1785). This law is extended by the Einstein mass-energy relationship, whichstatesthatmatterandenergyareinterchangeable.

ENERGY

DefinitionofEnergyThe concept of energy plays an important role in all of the sciences. In

chemistry, all physical and chemical changes have energy considerationsassociated with them. To understand how and why these changes happen, anunderstandingofenergyisrequired.Energyisdefinedasthecapacitytodowork.Workisdonewheneveraforce

isappliedoveradistance.Therefore,anythingthatcanforcemattertomove,tochange speed, or to change direction has energy. The following example willhelpyouunderstand thisdefinitionofenergy.Whenyouchargeabatterywithelectricity,youarestoringenergy in theformofchemicalenergy.Thechargedbatteryhasacapacitytodowork.Ifyouusethebatterytooperateatoycar,thestoredenergy is transformed intomechanical energy that exerts a forceon themechanism that turns the wheels and makes the car move. This processcontinuesuntilthechargeorstoredenergyiscompletelyused.Initsunchargedcondition,thebatterynolongerhasthecapacitytodowork.Work itself is measured in joules, and so is energy. In some problems,

however, energy may be expressed in kilocalories. The relationship betweenthesetwounitsisthat4.18×108joules(J)equals1kilocalorie(kcal).

FormsofEnergyEnergymayappearinavarietyofforms.Mostcommonly,energyinreactionsisevolved as heat. Some other forms of energy are light, sound, mechanicalenergy,electricalenergy,andchemicalenergy.Energycanbeconvertedfromone form to another, as when the heat from burning fuel is used to vaporizewatertosteam.Theenergyofthesteamisusedtoturnthewheelsofaturbinetoproducemechanicalenergy.Theturbineturnsthegeneratorarmaturetoproduceelectricity,which is then available in homes for use as light or heat, or in theoperationofmanymodernappliances.

Two general classifications of energy are potential energy and kineticenergy. Potential energy is stored energy due to overcoming forces in nature.Kinetic energy is energy of motion. The difference can be illustrated by abouldersittingonthesideofamountain.Ithasahighpotentialenergyduetoitsposition above the valley floor. If it falls, however, its potential energy isconverted to kinetic energy.This illustration is very similar to the situation ofelectrons cascading to lower energy levels in the atomic model described inChapter2.

TypesofReactions(ExothermicVersusEndothermic)Whenphysicalorchemicalchangesoccur,energychangesareinvolved.Changeof heat content can be designated asΔH. The heat content (H ) is sometimesreferred to as the enthalpy. Every system has a certain amount of heat. Thischangesduringthecourseofaphysicalorchemicalchange.Thechangeinheatcontent,ΔH,isthedifferencebetweentheheatcontentoftheproductsandthatofthereactants.Theequationis:

ΔH=Hproducts–Hreactants

If the heat content of the products is greater than the heat content of thereactants,ΔHisapositivequantity(ΔH>0)andthereactionisendothermic.If,however, the heat content of the products is less than the heat content of thereactants,ΔH is anegativequantity (ΔH < 0) and the reaction isexothermic.This relationship is shown graphically in Figures 1 and 2. This topic isdevelopedindetailinChapter8.

ConservationofEnergyExperiments have shown that energy is neither gained nor lost in physical orchemical changes. This principle is known as the Law of Conservation ofEnergyandisoftenstatedasfollows:Energyisneithercreatednordestroyedinordinaryphysicalandchemicalchanges.Ifthesystemunderstudylosesenergy,the reaction is exothermic and the ΔH is negative. Therefore, the system’ssurroundings must gain the energy that the system loses so that energy isconserved.

CONSERVATIONOFMASSANDENERGYWiththeintroductionofatomictheoryandamorecompleteunderstandingofthenatureofbothmassandenergy,itwasfoundthatarelationshipexistsbetweenthesetwoconcepts.EinsteinformulatedtheLawofConservationofMassandEnergy. This states that mass and energy are interchangeable under specialconditions. The conditions have been created in nuclear reactors andaccelerators,andthelawhasbeenverified.ThisrelationshipcanbeexpressedbyEinstein’sfamousequation:

E=mc2

Energy=Mass×(Velocityoflight)2

SCIENTIFICMETHODAlthoughsomediscoveriesaremadeinsciencebyaccident, inmostcases, thescientists involved use an orderly process to work on their projects anddiscoveries.Theprocessresearchersusetocarryouttheirinvestigationsisoftencalled the scientificmethod. It is a logical approach to solving problems byobserving and collecting data, formulating a hypothesis, and constructingtheories supported by the data. The formulating of a hypothesis consists ofcarefullystudyingthedatacollectedandorganizedtoseeifatestablestatementcanbemadewithregardtothedata.Thehypothesistakestheformofan“if…then” statement. If certain data are true, then a prediction can be madeconcerning the outcome. The next step is to test the prediction to see if itwithstandstheexperimentation.Thehypothesiscangothroughseveralrevisionsas the process continues. If the data from experimentation show that thepredictionsofthehypothesisaresuccessful,scientistsusuallytrytoexplainthephenomena by constructing amodel. The model can be a visual, verbal, ormathematicalmeansofexplaininghowthedataisrelatedtothephenomena.Thestagesofthisprocesscanbeillustratedbythediagramshownbelow:

MEASUREMENTSANDCALCULATIONSThestudentofchemistrymustbeabletomakegoodobservations.Observationsare either qualitative or quantitative. Qualitative observations involve

descriptions of the nature of the substances under investigation. Quantitativeobservations involve making measurements to describe the substances underobservation.Thechemistrystudentmustalsobeabletousecorrectmeasurementtermsandtherequiredmathematicalskillstosolvetheproblems.Thefollowingsectionsreviewthesetopics.

MetricSystemIt is important that scientists around the world use the same units whencommunicating information. For this reason, scientists use the modernizedmetric system, designated in 1960by theGeneralConference onWeights andMeasuresastheInternationalSystemofUnits.ThisiscommonlyknownasSI,an abbreviation for the French name Le Système International d’Unités. It isnow themost common systemofmeasurement in theworld. There areminordifferencesbetweentheSIandmetricsystems.Forthemostpart,thequantitiesareinterchangeable.

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Onlymetric units are used on theSATtest.

The reason SI is so widely accepted is twofold. First, it uses the decimalsystemasitsbase.Second,manyunitsforvariousquantitiesaredefinedintermsofunitsforsimplerquantities.There are seven basic units that can be used to express the fundamental

propertiesofmeasurement.ThesearecalledtheSIbaseunitsandareshowninthetablethatfollows.

*Thecandelaisrarelyusedinchemistry.

Other SI units are derived by combining prefixes with a base unit. Theprefixes representmultiplesor fractionsof10.Thefollowing tablegivessomebasicprefixesusedinthemetricsystem.

For an example of how a prefix works in conjunction with the base word,considerthetermkilometer.Theprefixkilo-means“multiplytherootwordby1,000,” soakilometer is1,000meters.By the same reasoning,amillimeter is1/1,000meter.Becauseoftheprefixsystem,allunitsandquantitiescanbeeasilyrelatedby

somefactorof10.Hereisabrieftableofsomemetricunitequivalents.

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Knowtheserelationships.

Length10millimeters(mm) = 1centimeter(cm)

100cm = 1meter(m)1,000m = 1kilometer(km)

Volume1,000milliliters(mL) = 1liter(L)

1,000cubiccentimeters(cm3) = 1liter1mL = 1cm3

Mass1,000milligrams(mg) = 1gram(g)

1,000g = 1kilogram(kg)

Aunitoflength,usedespeciallyinexpressingthelengthoflightwaves,isthenanometer,abbreviatedasnmandequalto10−9meter.BecauseintheUnitedStatesmeasurementsareoccasionallyreportedinunits

of the English system, it is important to be aware of somemetric to Englishsystem equivalents. Some common conversion factors are shown in thefollowingtable.

2.54centimeters = 1inch

1meter =39.37inches(10%longerthan1yard)

28.35grams = 1ounce454grams = 1pound1kilogram = 2.2pounds0.946liter = 1quart

1liter(5%largerthan1quart) = 1.06quarts

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Foryourinformationonly;metricisusedonthetest.

Themetricsystemstandardswerechosenasnaturalstandards.Themeterwasfirstdescribedasthedistancemarkedoffonaplatinum-iridiumbarbutnowisdefined as the length of the path traveled by light in a vacuum during a timeintervalof1/2.99792458×108second.Therearesomeinterestingrelationshipsbetweenvolumeandmassunitsinthe

metricsystem.Becausewaterismostdenseat4°C,thegramwasintendedtobe1cubiccentimeterofwateratthistemperature.Thismeans,then,that:

1,000cm3=1Lofwater@4°C

1,000 cm3 ofwaterweighs 1,000 g@4°C.

Therefore

1Lofwater@4°Cweighs1kg,

and

1mLofwater@4°Cweighs1g.

When1Lisfilledwithwater@4°C,ithasamassof1kg.

TemperatureMeasurementsThemost commonly used temperature scale in scientific work is theCelsiusscale. It gets its name from theSwedish astronomerAndersCelsius anddatesback to 1742. For a long time itwas called the centigrade scale because it isbased on the concept of dividing the distance on a thermometer between thefreezingpointofwateranditsboilingpointinto100equalmarkingsordegrees.Anotherscaleisbasedonthelowest theoretical temperature(calledabsolute

zero). This temperature has never actually been reached, but scientists inlaboratories have reached temperatureswithin about a thousandth of a degreeaboveabsolutezero.LordWilliamKelvinproposedthisscale,onwhichadegreeisthesamesizeasaCelsiusdegreeandwhichisreferredtoastheKelvinscale.Throughexperimentsandcalculations,ithasbeendeterminedthatabsolutezerois273.15degreesbelowzeroontheCelsiusscale.Thisfigureisusuallyroundedoffto–273°C.The diagram and conversion formulas that follow give the graphic and

algebraicrelationshipsamongthreetemperaturescales:theCelsiusandKelvin,commonlyusedinchemistry,andtheFahrenheit.

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Kelvinand°CunitsareusedontheSATtest.

Note: In Kelvin notation, the degree sign is omitted: 283 K. The unit is thekelvin,abbreviatedasK.

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REMEMBER The Kelvin unit isdesignatedwithKanddoesnothavethe“°”symbol.

EXAMPLE1:

EXAMPLE2:

HeatMeasurementsHeatenergy(orjustheat)isaformofenergythattransfersamongparticlesinasubstance(orsystem)bymeansofthekineticenergyofthoseparticles.Inotherwords,underkinetic theory,heat is transferredbyparticlesbouncing intoeachother.Thescalesaboveareusedtomeasurethedegreeofheat.Apailandathimble

canbothbe filledwithwater at 100°Celsius.Thewater inbothmeasures thesamedegreeofheat.However, thepailofwaterhasagreaterquantityofheat.Thiscouldbeeasilydemonstratedbytheamountoficethatcouldbemeltedbythewater in these twocontainers.Obviously, thepailofwaterat100°Celsiuswillmeltmore ice thanwill a thimble full of water at the same temperature.Therefore, thepailofwatercontainsagreaternumberofcaloriesofheat.Thecalorieunitisusedtomeasurethequantityofheat.Itisdefinedastheamountofheat needed to raise the temperature of 1 gram of water by 1 degree on theCelsius scale. This is a rather small unit to measure the quantities of heatinvolved inmost chemical reactions. Therefore, thekilocalorie is more oftenused. The kilocalorie equals 1,000 calories. It is the quantity of heat thatwillincreasethetemperatureof1kilogramofwaterby1degreeontheCelsiusscale.Althoughthecalorie iscommonlyusedineverydayusagewithregardtofood,theSIunitforheatenergyisthejoule.ItisabbreviatedasJand,becauseitisarather small unit, it is commonly given in kilojoules (kJ). The relationshipbetweenthecalorieandthejouleisthat1calorieequals4.18joules.Problems involving heat transfers in water are called water calorimetry

problemsandareexplainedin“WaterCalorimetryProblems”Chatper7.

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Becausethejouleisrathersmall,kJisusedmostoften.

ExponentialNotationWhen students must do mathematical operations with numerical figures, theexponential notation system is very useful. Basically this system uses theexponential means of expressing figures. With large numbers, such as3,630,000.,movethedecimalpointtotheleftuntilonlyonedigitremainstotheleft (3.630000)and then indicate thenumberofmovesof thedecimalpointastheexponentof10(3.63×106).Withaverysmallnumbersuchas0.000000123,move the decimal point to the right until only one digit is to the left(0000001.23)andthenexpressthenumberofmovesasthenegativeexponentof10(1.23×10−7).

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Scientific notation is based onexponentsof10.

With numbers expressed in this exponential form, you can now use yourknowledge of exponents in mathematical operations. An important fact torememberisthatinmultiplicationyouaddtheexponentsof10,andindivisionyousubtracttheexponents.Additionandsubtractionoftwonumbersexpressedin scientific notation can be performed only if the numbers have the sameexponent.

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REMEMBER Only one digit canbetotheleftofthedecimalpoint.

EXAMPLES:

Multiplications:(2.3×105)(5.0×10−12).Multiplyingthefirstnumbers,youget11.5,andadditionoftheexponentsgives10−7.Now,changingtoanumberwithonlyonedigittotheleftofthedecimalpointgivesyou1.15×10−6fortheanswer.

Trythese:

(5.1×10−6)(2×10−3)=10.2×10−9=1.02×10−8

(3×105)(6×103)=18×108=1.8×109

Divisions:(1.5×103)÷(5.0×10−2)=0.3×105=3×104(2.1×10−2)÷(7.0×10−3)=0.3×101=3(Noticethatindivisiontheexponentsof10aresubtracted.)

Additionandsubtraction:(4.2×104kg)+(7.9×103kg)=(4.2×104kg)+(0.79×104kg)(notethattheexponentsof10arenowthesame)=4.99×

104kgThiscanberoundedto5.0×104kg.

(6.02×10−3)–(2.41×10−4)=(6.02×10−3)–(.241×10−3)(notethattheexponentsof10arenowthesame)=5.779×10−3or5.8×10−3whenroundedtotwosignificantfigures.

DimensionalAnalysis(Factor-LabelMethodofConversion)When you are working problems that involve numbers with units ofmeasurement, it is convenient to use this method so that you do not becomeconfusedintheoperationsofmultiplicationordivision.Forexample,ifyouarechanging0.001kilogramtomilligrams,yousetupeachconversionasafractionsothatalltheunitswillfactoroutexcepttheoneyouwantintheanswer.

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Cancel out all units except the onefortheanswer.

Notice that the kilogram ismade the denominator in the first fraction to befactored with the original kilogram unit. The numerator is equal to thedenominatorexceptthatthenumeratorisexpressedinsmallerunits.Thesecondfractionhasthegramunitinthedenominatortobefactoredwiththegramunitintheprecedingfraction.Theanswerisinmilligramsbecausethisistheonlyunitremaininganditassuresyouthatthecorrectoperationshavebeenperformedintheconversion.

ANOTHEREXAMPLE:

Thefactor-labelmethodisusedinexamplesthroughoutthisbook.

Precision,Accuracy,andUncertaintyTwo other factors to consider in measurement are precision and accuracy.Precisionindicatesthereliabilityorreproducibilityofameasurement.Accuracyindicateshowcloseameasurementistoitsknownoracceptedvalue.

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Accuracy is how close you havecometothetruevalue.

Forexample,supposeyouweretakingareadingoftheboilingpointofpurewateratsealevel.Usingthesamethermometerinthreetrials,yourecord96.8,96.9,and97.0degreesCelsius.Sincethesefiguresshowahighreproducibility,youcansaythattheyareprecise.However,thevaluesareconsiderablyofffromtheacceptedvalueof100degreesCelsius, sowesay theyarenotaccurate. Inthisexampleweprobablywouldsuspectthattheinaccuracywasthefaultofthethermometer.

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Precision is how repeatable theresultsare.

Regardless of precision and accuracy, all measurements have a degree ofuncertainty. This is usually dependent on one or both of two factors—thelimitation of themeasuring instrument and the skill of the personmaking themeasurement.Uncertaintycanbestbeshownbyexample.

Thegraduated cylinder in the illustration contains a quantity ofwater to bemeasured.Itisobviousthatthequantityisbetwen30and40millilitersbecausethemeniscus lies between these twomarked quantities.Now, checking to seewhere the bottom of themeniscus lies with reference to the ten interveningsubdivisions,weseethatitisbetweenthefourthandfifth.Thismeansthatthevolume lies between 34 and 35 milliliters. The next step introduces theuncertainty. We have to guess how far the reading is between these twomarkings.Wecanmakeanapproximateguess,orestimate,thatthelevelismorethan0.2butlessthan0.4ofthedistance.Wethereforereportthevolumeas34.3milliliters.The lastdigit inanymeasurement isanestimateof thiskindand isuncertain.

SignificantFiguresAny time ameasurement is recorded, it includes all the digits that are certainplus one uncertain digit. These certain digits plus the one uncertain digit arereferred to as significant figures. Themore digits you are able to record in ameasurement, the less relative uncertainty there is in the measurement. Thefollowingtablesummarizestherulesofsignificantfigures.

One last ruledealswith final zeros in awholenumber.These zerosmayormaynotbesignificant,dependingonthemeasuringinstrument.Forinstance,ifaninstrumentthatmeasurestothenearestmileisused,thenumber3,000mileshasfoursignificantfigures.If,however,theinstrumentinquestionrecordsmilesto the nearest thousands, there is only one significant figure. The number ofsignificantfigures in3,000couldbeone, two, three,or four,dependingon thelimitationofthemeasuringdevice.Thisproblemcanbeavoidedbyusing thesystemof scientificnotation.For

thisexample,thefollowingnotationswouldindicatethenumbersofsignificantfigures:

3×103 onesignificantfigure3.0×103 twosignificantfigures3.00×103 threesignificantfigures3.000×103 foursignificantfigures

CalculationswithSignificantFiguresWhenyoudocalculationsinvolvingnumbersthatdonothavethesamenumberofsignificantfiguresineach,keepthefollowingtworulesinmind.

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RULE Your answer cannot have

more significant figures than thequantityhavingthefewestnumberofsignificantfigures.

First, in multiplication and division, the number of significant figures in aproduct or a quotient of measured quantities is the same as the number ofsignificant figures in the quantity having the smaller number of significantfigures.

EXAMPLE1

Problem Unroundedanswer

Answerroundedtothe

correctnumberofsignificantfigures

4.29cm×3.24cm= 13.8996cm2= 13.9cm2

Explanation:Bothmeasuredquantitieshavethreesignificantfigures.Therefore,theanswershouldberoundedtothreesignificantfigures.

EXAMPLE2

Problem Unroundedanswer

Answerroundedtothe

correctnumberofsignificantfigures

4.29cm×3.2cm= 13.728cm2= 14cm2

Explanation: One of themeasured quantities has only two significant figures.Therefore,theanswershouldberoundedtotwosignificantfigures.

EXAMPLE3

Problem Unroundedanswer

Answerroundedtothe

correctnumberofsignificantfigures

8.47cm2/4.26cm= 1.9882629cm= 1.99cm

Explanation:Bothmeasuredquantitieshavethreesignificantfigures.Therefore,theanswershouldberoundedtothreesignificantfigures.

Second, when adding or subtracting measured quantities, the sum ordifference should be rounded to the same number of decimal places as thequantityhavingtheleastnumberofdecimalplaces.

EXAMPLE1

Problem Unroundedanswer

Answerroundedtothe

correctnumberofsignificantfigures

3.56cm2.6cm+6.12cmTotal= 12.28cm 12.3cm

Explanation:Oneofthequantitiesaddedhasonlyonedecimalplace.Therefore,theanswershouldberoundedtoonlyonedecimalplace.

EXAMPLE2

Problem Unroundedanswer

Answerroundedtothe

correctnumberofsignificantfigures

3.514cm–2.13cmDifference= 1.384cm= 1.38cm

Explanation:Oneofthequantitieshasonlytwodecimalplaces.Therefore,theanswershouldberoundedtoonlytwodecimalplaces.

ChapterSummaryThefollowingtermssummarizealltheconceptsandideasthatwereintroduced

inthischapter.Youshouldbeabletoexplaintheirmeaningandhowyouwouldusetheminchemistry.Theyappearinboldfacetypeinthischaptertodrawyourattentiontothem.Theboldfacetypealsomakesiteasierforyoutolookthemupif you need to. You could also use the search or “Google” action on yourcomputer to get a quick and expanded explanation of these terms, laws, andformulas.

accuracy gas matteractivationenergy heatenergy meniscuscalorie heterogeneous mixtureCelsius homogeneous physicalchangechemicalchange inertia physicalpropertychemicalproperty joule potentialenergycompound Kelvin precisiondensity kilocalorie significantfigureselement kilojoule SIunitsendothermic kineticenergy solidexothermic liquid uncertaintyexponentialnotation mass

LawofConservationofEnergyLawofConservationofMatterLawofConservationofMassandEnergyLawofDefiniteCompositionorProportion

InternetResourcesOnlinecontent that reinforces themajorconceptsdiscussed in thischaptercanbefoundatthefollowingInternetaddressesiftheyarestillavailable.Somemayhavebeenchangedordeleted.TheClassificationofMatterhttp://www.teacherbridge.org/public/bhs/teachers/Dana/Matter.html

Thissiteexplainsthedifferencesamongtypesofmatterandprovidesexercisestocheckyourunderstanding.TheScientificMethodhttp://en.wikipedia.org/wiki/ScientificmethodThissitegivesanhistoricaloverviewofexamplesofusingthescientificmethod.TheSISystemhttp://en.wikipedia.org/wiki/InternationalSystemofUnitsThissitegivesanoverviewoftheSISystemaswellasanhistoricalandaglobalviewofthesystem.

PracticeExercises

1.1.2mg =____________ g

2.6.3cm =____________ mm

3.5.12m =____________ cm

4.32°C =____________ K

5.6.111mL =____________ L

6.1km =____________ mm

7.1.03kg =____________ g

8.0.003g =____________ kg

9.22.4L =____________ mL

10.10,013cm =____________ km

11.ThedensityofCCl4(carbontetrachloride)is1.58grams/milliliter.Whatwill100.millilitersofCCl4weigh?

12.Themassofapieceofsulfuris227grams.Whenitwassubmergedinagraduatedcylindercontaining50.0millilitersofH2O,thelevelroseto150.milliliters.Whatisthedensity(g/mL)ofthesulfur?

13.(a)Abox20.0centimeters×20.0centimeters×5.08incheshaswhatvolumeincubiccentimeters?

(b)Whatmass,ingrams,ofH2O@4°Cwilltheboxhold?

14.Setupthefollowingusingthedimensionalanalysismethod:

15.Howmanysignificantfiguresareineachofthefollowing?

(a)1.01(b)200.0(c)0.0021(d)0.0230

16.Abakingpowdercancarriesthestatement,“Ingredients:cornstarch,sodiumbicarbonate,calciumhydrogenphosphate,andsodiumaluminumsulfate.”Therefore,thisbakingpowderis

(A)acompound(B)amixture(C)amolecule(D)amixtureofelements

17.Whichofthefollowingisaphysicalpropertyofsugar?

(A)Itdecomposesreadily.(B)Itscompositioniscarbon,hydrogen,andoxygen.(C)ItturnsblackwithconcentratedH2SO4.(D)Itcanbedecomposedwithheat.(E)Itisawhitecrystallinesolid.

18.Asubstancethatcanbefurthersimplifiedusingordinarymeansmaybeeither

(A)anelementoracompound

(B)anelementoramixture(C)amixtureoracompound(D)amixtureoranatom

19.ChemicalactionmayinvolveallofthefollowingEXCEPT

(A)combiningofatomsofelementstoformamolecule(B)separationofthemoleculesinamixture(C)breakingdowncompoundsintoelements(D)reactingacompoundandanelementtoformanewcompoundanda

newelement

20.Theenergyofasystemcanbe

(A)easilychangedtomass(B)transformedintoadifferentform(C)measuredonlyaspotentialenergy(D)measuredonlyaskineticenergy

21.IftheΔHofareactionisanegativequantity,thereactionisdefinitely

(A)endothermic(B)unstable(C)exothermic(D)reversible

22.WriteEforeachelement,Cforeachcompound,andMforeachmixtureinthefollowinglist:

Water Aluminumoxide HydrochloricacidWine Hydrogen NitrogenSoil Carbondioxide TinSilverchloride Air Potassium

ThefollowingquestionsareintheformatthatisusedontheSATSubjectTestin Chemistry. If you are not familiar with these types of questions, study“WhatTypesofQuestionsAppearontheTest”intheIntroductionbeforedoingtheremainderofthereviewquestions.

23.Ifthegraphicrepresentationoftheenergylevelsofthereactantsand

productsinachemicalreactionlookslikethis:

Whichofthefollowingstatementsaretrue?I.Theactivationenergyfortheforwardreactionisrepresentedbythe“a”

portion.II.Theactivationenergyfortheforwardreactionisrepresentedbythe“b”

portionofthegraph.III.The“a”portionistheenergygivenoffintheforwardreaction.

(A)Ionly(B)IIonly(C)IandIIIonly(D)IIandIIIonly(E)I,II,andIII

24.Asubstancethatcanbefurthersimplifiedbyordinarychemicalmeansmaybewhichofthefollowing?

I.AnelementoracompoundII.AmixtureoracompoundIII.Anelementofamixture

(A)Ionly(B)IIonly(C)IIIonly(D)IandIIonly(E)I,II,andIII

Questions25–29refertothefollowingterms.

(A)Density(B)Asolid(C)Volume(D)Weight(E)Matter

25.Givesthemassperunitvolume

26.Hasmassandadefinitesizeandshape

27.Givesthespaceoccupied

28.Hasmassandoccupiesspace

29.Definedasameasureofthemasstimesthegravitationalforce

Directions:(SeetheexplanationforthistypeofquestionandtheexamplesonPartBoftheIntroductionbeforeattemptingquestions30–32.)

Every question below contains two statements, I in the left-hand columnandIIintheright-handcolumn.Foreachquestion,decideifstatementIistrue or false and whether statement II is true or false, and fill in thecorrespondingTorFovals in theanswerspaces.*Fill inovalCEonly ifstatementIIisacorrectexplanationofstatementI.

I II

30.

Asubstancecomposedoftwoormoreelementschemicallycombinediscalledamixture

BECAUSEthepropertiesoftheconstituentsofamixtureareretained.

31.

Achemicalchangeinvolveschangeinthecompositionandmolecularstructureofthereactants

BECAUSE

inachemicalreactionbondsarebrokenandnewsubstancesandnewbondsareformed.

Theburningofpaperiswhenachemicalchangeoccursenergyiseither

32. aphysicalchange BECAUSE gainedorlostbythereactants.

*FillinovalCEonlyifIIisacorrectexplanationofI.

AnswersandExplanations1.0.0012g

2.63mm

3.512cm

4.305K32°C+273=305K

5.0.006111L

6.1,000,000or1×106mm

7.1.03×103kg

8..000003kgor3×10–6kg

9.22,400or2.24×104mL

10..10013km

11.158gBecausethedensityis1.58g/mLandyouwanttheweightof100mL,youusetheformulathatdensity×volume=weight.

Insertingthevaluesgives

12.2.27g/mL

Tofindthevolumeof227gofsulfur,subtractthevolumeofwaterbeforefromthevolumeafterimmersion.

150.mL−50.mL=100.mLThen

13.(a)5,160cm3(b)5,160g

(a)Convert5.08in.tocentimeters:

Then20.0cm×20.0cm×12.9cm=5,160cm3

(b)Since1.00cm3ofwaterat4°Chasamassof1.00g,then5,160cm3=5,160g

14.

15.(a)3(b)4(c)2(d)3

16.(B)Becauseallthesubstancesarecompounds.

17.(E)Becausealltheotherstatementsrefertochemicalpropertiesofsugar.

18.(C)Neitheranelementnoranatomcanbesimplifiedintoanythingelsebyordinarymeans.

19.(B)Separatingmoleculesinamixture(e.g.,evaporatingwaterfromasugarsolution)doesnotinvolveachemicalchangeaction.

20.(B)Becausetheotherchoicesarenottrue.Transformingenergyintodifferentformscanbedemonstratedbybatteriesinaflashlight,changingchemicalenergyintoelectricalenergyandthenintolightenergy.

21.(C)AnytimetheΔHofareactionisnegative,thereactiongivesoffenergyand,itisclassifiedasexothermic.

22.

23.(A)Inthediagrampartofquestion23

“a”istheactivationenergyfortheforwardreaction.Thesumof“a”and“b”istheactivationenergyforthereversereaction,and“b”aloneistheenergygivenoffbytheforwardreaction.

24.(B)Becauseanelementisabasicbuildingblockintheperiodictable,itcannotbefurthersimplifiedbyordinarychemicalmeans.Acompoundandamixturecanbesimplifiedbychemicalandphysicalmeans,respectively.

25.(A)Themassperunitvolumeisthedefinitionofdensity.

26.(B)Matterthathasmassandadefinitesizeandshapeiscalledasolid.

27.(C)Thespaceoccupiedbyasubstanceiscalleditsvolume.

28.(E)Thatasubstanceoccupiesspaceandmassisthebasicdefinitionofallmatter.

29.(D)Weightistheproductofmasstimesagravitationalforce.Inouterspacewherethereisnogravitationalforce,wesayamassisweightless.

30.(F,T)ThecolumnIstatementisfalse,becauseamixtureiselementsand/orcompoundsinphysicalcontact(withoutbonds)withoneanother.

31.(T,T,CE)Chemicalreactionsinvolvethechangingofmolecularstructuresbythebreakingofbondsandtheformationofnewbonds.

32.(F,T)Burningpaperisachemicalreactionnotaphysicalone.ThestatementincolumnIIistrue,becauseachemicalchangealwaysinvolvesanenergychange.

CHAPTER2

AtomicStructureandthePeriodicTableoftheElements

TheseskillsareusuallytestedontheSATSubjectTestinChemistry.Youshouldbeableto...•Describethehistoryofthedevelopmentofatomictheory.•Explainthestructureofatoms,theirmainenergylevels,sublevels,orbitalconfiguration,andtherulesthatgovernhowtheyarefilled.

•Placeatomsingroupsandperiodsbasedontheiratomicstructure.•Writeformulasandnamesofcompounds.•ExplainhowchemicalandphysicalpropertiesarerelatedtopositionsinthePeriodicTable,includingatomicsize,ionicsize,electronegativity,acid-formingproperties,andbase-formingproperties.

•Explainthenatureofradioactivity,thetypesandcharacteristicsofeach,andtheinherentdangers.

•Identifythechangesthatoccurinadecayseries.•Dothemathematicalcalculationstodeterminetheageofasubstanceusingitshalf-life.

This chapter will review and strengthen these skills. Be sure to do thePracticeExercisesattheendofthechapter.

Theideaofsmall,invisibleparticlesbeingthebuildingblocksofmattercanbetraced backmore than 2,000 years to theGreek philosophersDemocritus andLeucippus.Theseparticles,consideredtobesosmallandindestructiblethattheycouldnotbedividedintosmallerparticles,werecalledatoms, theGreekwordforindivisible.TheEnglishwordatomcomesfromthisGreekword.Thisearlyconceptofatomswasnotbaseduponexperimentalevidencebutwassimplyaresultofthinkingandreasoningonthepartofthephilosophers.Itwasnotuntilthe eighteenth century that experimental evidence in favor of the atomichypothesis began to accumulate. Finally, around 1805, John Dalton proposed

some basic assumptions about atoms based on what was known throughscientific experimentation andobservation at that time.These assumptions arevery closely related to what scientists presently know about atoms. For thisreason,Daltonisoftenreferredtoasthefatherofmodernatomictheory.Someofthesebasicideaswere:

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Know Dalton’s five basic ideasaboutatoms.

1.Allmatterismadeupofverysmall,discreteparticlescalledatoms.

2.Allatomsofanelementarealikeinweight,andthisweightisdifferentfromthatofanyotherkindofatom.

3.Atomscannotbesubdivided,created,ordestroyed.

4.Atomsofdifferentelementscombineinsimplewhole-numberratiostoformchemicalcompounds.

5.Inchemicalreactions,atomsarecombined,separated,orrearranged.

By the secondhalfof the1800s,many scientistsbelieved that all themajordiscoveriesrelatedtotheelementshadbeenmade.Theonlythingleftforyoungscientiststodowastorefinewhatwasalreadyknown.ThiscametoasuprisinghaltwhenJ.J.Thomsondiscoveredtheelectronbeaminacathoderaytubein1897.Soonafterward,HenriBecquerelannouncedhisworkwith radioactivity,andMarieCurieandherhusband,Pierre,setabouttryingtoisolatethesourceofradioactivityintheirlaboratoryinFrance.

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KnowNielsBohr’smodelbasedonaplanetary model as opposed toquantum theory based on aprobabilitymodel.

During the late nineteenth and early twentieth centuries, more and more

physiciststurnedtheirattentiontothestructureoftheatom.In1913theDanishphysicist Niels Bohr published a theory explaining the line spectrum ofhydrogen.Heproposedaplanetarymodelthatquantizedtheenergyofelectronsto specific orbits. Thework of Louis de Broglie and others in the 1920s and1930s showed that quantum theory described a more probabilistic model ofwheretheelectronscouldbefoundthatresultedinthetheoryoforbitals

ELECTRICNATUREOFATOMSFrom around the beginning of the twentieth century, scientists have beengatheringevidenceaboutthestructureofatomsandfittingtheinformationintoamodeloftheatomicstructure.

BasicElectricChargesThediscoveryof theelectronas thefirstsubatomicparticle iscredited toJ.J.Thomson(England,1897).Heusedanevacuatedtubeconnectedtoasparkcoilas shown in Figure 3. As the voltage across the tube was increased, a beambecamevisible.Thiswasreferred toasacathoderay.Thomsonfound that thebeam was deflected by both electrical and magnetic fields. Therefore, heconcluded that cathode rays are made up of very small, negatively chargedparticles,whichbecameknownaselectrons.

Figure3.CathodeRayTube

FurtherexperimentationledThomsontofindtheratiooftheelectricalchargeof the electron to its mass. This was a major step toward understanding thenature of the particle. He was awarded a Nobel Prize in 1906 for hisaccomplishment.It was an American scientist,Robert Millikan, who in 1909 was able to

measurethechargeonanelectronusingtheapparatuspicturedinFigure4.

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Millikan’s experiment determinedthemassofanelectron.

FIGURE4.MillikanOilDropExperiment

Oil droplets were sprayed into the chamber and, in the process, becamerandomlychargedbygainingorlosingelectrons.Theelectricfieldwasadjustedsothatanegativelychargeddropwouldmoveslowlyupwardinfrontofthegridinthetelescope.Knowingtherateatwhichthedropwasrising,thestrengthofthefield,andthemassofthedrop,Millikanwasabletocalculatethechargeonthe drop. Combining the information with the results of Thomson, he couldcalculateavalueforthemassofasingleelectron.Eventually,thisnumberwasfoundtobe9.11×10−28gram.ErnestRutherford(England,1911)performedagoldfoilexperiment(Figure

5)thathadtremendousimplicationsforatomicstructure.

FIGURE5.Rutherford’sExperiment

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Rutherford’s experiment using alphaparticles confirmed that there wasmostly empty space between thenucleusandelectrons.

Alphaparticles(heliumnuclei)passed throughthefoilwithfewdeflections.However,somedeflections(1per8,000)werealmostdirectlyback toward thesource.Thiswasunexpectedandsuggestedanatomicmodelwithmostlyemptyspacebetweenanucleus,inwhichmostofthemassoftheatomwaslocatedandwhichwaspositivelycharged,andtheelectronsthatdefinedthevolumeof theatom.Aftertwoyearsofstudyingtheresults,Rutherfordfinallycameupwithanexplanation. He reasoned that the rebounded alpha particles must haveexperienced some powerful forcewithin the atom.And he assumed this forcemustoccupyaverysmallamountofspace,becausesofewalphaparticleshadbeendeflected.Heconcludedthattheforcemustbeadenselypackedbundleofmatter with a positive charge. He called this positive bundle the nucleus. Hefurtherdiscovered that thevolumeofanucleuswasverysmallcomparedwiththe totalvolumeofanatom.If thenucleuswere thesizeofamarble, then theatomwould be about the size of a football field.The electrons, he suggested,surrounded the positively charged nucleus like planets around the sun, eventhoughhecouldnotexplaintheirmotion.Further experiments showed that the nucleus was made up of still smaller

particles called protons. Rutherford realized, however, that protons, bythemselves,couldnotaccount for theentiremassof thenucleus.Hepredictedtheexistenceofanewnuclearparticlethatwouldbeneutralandwouldaccountfor the missing mass. In 1932, James Chadwick (England) discovered thisparticle,theneutron.Today the number of subatomic particles identified and named as discrete

unitshasrisentowellover90.

BohrModeloftheAtomIn1913,NielsBohr (Denmark)proposedhismodelof theatom.Thispicturedtheatomashavingadense,positivelychargednucleusandnegativelychargedelectronsinspecificsphericalorbits,alsocalledenergylevelsorshells,aroundthisnucleus.Theseenergylevelsarearrangedconcentricallyaroundthenucleus,andeachlevelisdesignatedbyanumber:1,2,3,...Theclosertothenucleus,thelessenergyanelectronneedsinoneoftheselevels,butithastogainenergytogofromoneleveltoanotherthatisfartherawayfromthenucleus.Becauseof itssimplicityandgeneralability toexplainchemicalchange, the

Bohrmodelstillhassomeusefulnesstoday.

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Bohr’s electron distribution toprincipal energy levels has theformula2n2.

ComponentsofAtomicStructure

Thechartbelowlists thebasicparticlesof theatomandimportant informationaboutthem.

(Therearenowsome30ormorenamedparticlesorunitsofatomicstructure,buttheabovearethemostcommonlyused.)

Whenthesecomponentsareusedin themodel, theprotonsandneutronsareshowninthenucleus.Theseparticlesareknownasnucleons.Theelectronsareshownoutsidethenucleus.The number of protons in the nucleus of an atom determines the atomic

number.Allatomsofthesameelementhavethesamenumberofprotonsandtherefore the same atomic number; atoms of different elements have differentatomic numbers. Thus, the atomic number identifies the element. An Englishscientist,HenryMoseley, firstdetermined theatomicnumbersof theelementsthroughtheuseofxrays.Thesumofthenumberofprotonsandthenumberofneutronsinthenucleus

iscalledthemassnumber.Table1summarizestherelationshipsjustdiscussed.Noticethattheoutermost

energylevelcancontainnomorethaneightelectrons.Theexplanationofthisisgiveninthenextsection.In some cases, different types of atoms of the same element have different

masses. For example, three types of hydrogen atoms are known. The mostcommontypeofhydrogen,sometimescalledprotium,accountsfor99.985%ofthehydrogenatomsfoundonEarth.Thenucleusofaprotiumatomcontainsoneproton only, and it has one electron moving about it. The second form ofhydrogen,knownasdeuterium,accountsfor0.015%ofEarth’shydrogenatoms.Eachdeuteriumatomhasanucleuscontainingoneprotonandoneneutron.Thethirdformofhydrogen,tritium,isradioactive.Itexistsinverysmallamountsinnature,butitcanbepreparedartificially.Eachtritiumatomcontainsoneproton,twoneutrons,andoneelectron.Protium,deuterium,andtritiumareisotopesofhydrogen.Isotopesareatoms

of the same element that have different masses. The isotopes of a particular

elementallhavethesamenumberofprotonsandelectronsbutdifferentnumbersofneutrons. Inall three isotopesofhydrogen, thepositivechargeof thesingleprotonisbalancedbythenegativechargeoftheelectron.Mostelementsconsistofmixturesofisotopes.Tin,forexample,hastenstableisotopes,themostofanyelement.

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Isotopes have the same atomicnumber but a different atomicmass.Thismeanstheydifferinthenumberofneutrons,notprotons.

ThepercentageofeachisotopeinthenaturallyoccurringelementonEarthisnearlyalwaysthesame,nomatterwheretheelementisfound.Thepercentageatwhicheachofanelement’sisotopesoccursinnatureistakenintoaccountwhencalculating the element’s average atomic mass.Average atomic mass is theweightedaverageoftheatomicmassesofthenaturallyoccurringisotopesofanelement.

*AcompletelistofthenamesandsymbolsoftheknownelementscanbefoundintheTablesforReferencesection.**PELisusedtorepresenttheprincipalenergylevels.

CalculatingAverageAtomicMassThe average atomic mass of an element depends on both the mass and therelative abundance of each of the element’s isotopes. For example, naturallyoccurring copper consists of 69.17% copper-63,which has an atomicmass of62.919598amu, and30.83%copper-65,whichhas anatomicmassof64.927793amu.Theaverageatomicmassofcoppercanbecalculatedbymultiplyingtheatomicmassofeachisotopebyitsrelativeabundance(expressedindecimalform)andaddingtheresults.

0.6917×62.919598amu+0.3083×64.927793amu=63.55amu

Therefore, thecalculatedaverageatomicmassofnaturallyoccurringcopper is63.55amu.AverageatomicmassesoftheelementslistedinthePeriodicTable,rounded to one decimal place for use in calculations and also in full to fourdecimal places, are given in the Chemical Elements table in the Tables forReferencesection.

ValenceElectronsEach atom attempts to have its outer energy level complete and accomplishesthisbyborrowing, lending,or sharing itselectrons.Theelectrons found in theoutermost energy level are called valence electrons. The remainder of theelectrons are called core electrons. The absolute number of electrons gained,lost,orborrowedisreferredtoasthevalenceoftheatom.

Thispicturecanbesimplified to , showingonly thevalenceelectronsasdotsinanelectrondotnotation.ThisiscalledtheLewisstructureoftheatom.Tocompleteitsouterorbittoeightelectrons,chlorinemustborrowanelectronfrom another atom. Its valence number then is 1. As stated above, whenelectronsaregained,weassigna–signtothisnumber,sotheoxidationnumberofchlorineis–1.

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A Lewis structure shows the atomicsymbol to represent the nucleus andinnershellelectrons.Itshowsdotstorepresentthevalenceelectrons.

Sincesodiumtendstolosethiselectron,itsoxidationnumberis+1.

ATOMICSPECTRATheBohrmodelwasbasedonasimplepostulate.Bohrappliedtothehydrogenatomtheconceptthattheelectroncanexistonlyincertainenergylevelswithoutanenergychangebutthat,whentheelectronchangesitsstate,itmustabsorboremit the exact amount of energy thatwill bring it from the initial state to thefinalstate.Thegroundstateisthelowestenergystateavailabletotheelectron.Theexcitedstate is any levelhigher than theground state.The formula for achangeinenergy(ΔE)is:

ΔEelectron=Efinal–Einitial

When an electronmoves from the ground state to an excited state, it mustabsorbenergy.Whenitmovesfromanexcitedstatetothegroundstate,itemitsenergy.Thisreleaseofenergyisthebasisforatomicspectra.(SeeFigure6.)TheenergyvaluesshownwerecalculatedfromBohr’sequation.

Figure6.AtomicSpectraChart

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When electrons drop to the lowestavailable energy level, they releaseenergy.

Whenenergyisreleasedinthe“allowed”values,itisreleasedintheformofdiscrete radiant energy called photons. Each of the first three levels has aparticular name associated with the emissions that occur when an electronreaches its ground state on that level. The emissions, consisting of ultravioletradiation,thatoccurwhenanelectroncascadesfromalevelhigherthanthefirstleveldownton=1areknownas theLymanseries.Note inFigure6 that thenexttwohigherlevelshavethenamesBalmer(forn=2)andPaschen(n=3)series,respectively.

SpectroscopyWhen the light emitted by energized atoms is examined with an instrumentcalled a spectroscope, the prism or diffraction grating in the spectroscopedisperses the light to allow an examination of the spectra or distinct coloredlines.Sinceonlyparticularenergyjumpsareavailableineachtypeofatom,eachelement has its own unique emission spectra made up of only the lines ofspecificwavelength thatcorrespond to itsatomicstructure.The relationshipofwavelengthtofrequencyisshownbelow.

Apartialatomicspectrumforhydrogenwouldlooklikethis:

Theright-handgroupisinthevisiblerangeandispartoftheBalmerseries.Theleft-handgroupisintheultravioletregionandbelongstotheLymanseries.Spectral lines like these can be used in the identification of unknown

specimens.

MassSpectroscopyAnother tool used to identify specific atomic structures is mass spectroscopy,

whichisbasedontheconceptthatdifferencesinmasscausedifferencesinthedegree of bending that occurs in a beam of ions passing through a magneticfield.ThisisshowninFigure7.

Figure7.MassSpectroscope

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A mass spectroscope separatesisotopes of the same element basedondifferencesintheirmass.

Theintensityonthephotographicplateindicatestheamountofeachparticularisotope. Other collectors may be used in place of the photographic plate tocollectandinterpretthesedata.

THEWAVE-MECHANICALMODELIn the early 1920s, some difficulties with the Bohr model of the atom werebecoming apparent. Although Bohr used classical mechanics (which is thebranch of physics that dealswith themotion of bodies under the influence offorces)tocalculatetheorbitsofthehydrogenatom,thisdisciplinedidnotservetoexplaintheabilityofelectronstostayinonlycertainenergylevelswithoutthelossofenergy.Norcoulditexplainwhyachangeofenergyoccurredonlywhenan electron “jumped” from one energy level to another and why the electroncouldnotexistintheatomatanyenergylevelbetweentheselevels.AccordingtoNewton’s laws, the kinetic energy of a body always changes smoothly and

continuously, not in sudden jumps.The ideaofonly certainquantizedenergylevelsbeingavailable in theBohratomwasavery importantone.Theenergylevels explained the existence of atomic spectra, described in the precedingsections.Anotherdifficultywith theBohrmodelwas that itworkedwellonlyfor the

hydrogenatomwithitssingleelectron.Itdidnotworkwithatomsthathadmoreelectrons.Anewapproachtothelawsgoverningthebehaviorofelectronsinsidetheatomwasneeded,andsuchanapproachwasdevelopedinthe1920sbythecombinedworkofmanyscientists.Theirworkdealtwithamoremathematicalmodelusuallyreferredtoasquantummechanicsorwavemechanics.By thistime,AlbertEinsteinhadalreadyproposedarelativitymechanicsmodeltodealwiththerelativenatureofmassasitsspeedapproachesthespeedoflight.Inthesamemanner,aquantum/wavemechanicsmodelwasnowneededtofitthedataoftheatomicmodel.MaxPlancksuggestedinhisquantumtheoryoflightthatlighthasbothparticlelikepropertiesandwavelikecharacteristics.In1924,Louisde Broglie, a young French physicist, suggested that, if light can have bothwavelikeandparticlelikecharacteristicsasPlanckhadsuggested, thenperhapsparticlescanalsohavewavelikecharacteristics.In1927,deBroglie’sideaswereverifiedexperimentallywheninvestigatorsshowedthatelectronscouldproducediffraction patterns, a property associatedwithwaves.Diffraction patterns areproducedbywavesastheypassthroughsmallholesornarrowslits.In 1927,Werner Heisenberg stated what is now called the uncertainty

principle. This principle states that it is impossible to know both the preciselocation and precise velocity of a subatomic particle at the same time.Heisenberg, in conjunction with the Austrian physicist Erwin Schrödinger,agreedwiththedeBroglieconceptthattheelectronisboundtothenucleusinamannersimilartoastandingwave.Theydevelopedthecomplexequationsthatdescribe the wave-mechanical model of the atom. The solution of theseequationsgivesspecificwavefunctionscalledorbitals.Thesearenotrelatedatall to the Bohr orbits. The electron does not move in a circular orbit in thismodel.Rather,theorbitalisathree-dimensionalregionaroundthenucleusthatindicatestheprobablelocationofanelectronbutgivesnoinformationaboutitspathway. The drawings in Figures 8a and 8b are only probability distributionrepresentationsofwhereelectronsintheseorbitalsmightbefound.

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Knowtheuncertaintyprinciple

QuantumNumbersandthePauliExclusionPrincipleEach electron orbital of an atommay be described by a set of four quantumnumbers in thewave-mechanicalmodel.Thesenumbersgive thepositionwithrespect to the nucleus, the shape of the orbital, its spatial orientation, and thespinoftheelectronintheorbital.Principalquantumnumber(n)1,2,3,4,5,etc.

Thevaluesofn=1,2,3...

Thisnumberreferstoaveragedistanceoftheorbitalfromthenucleus.1isclosesttothenucleusandhastheleastenergy.ThenumberscorrespondtotheorbitsintheBohrmodel.Theyarecalledenergylevels.

Angularmomentum( )quantumnumbers,p,d,f(inorderofincreasingenergy)

Thevalueof can=0,1,...,n−1=0indicatesaspherical-shapedsorbital=1,indicatesadumbbell-shapedporbital=2,indicatesafiveorbitalorientationdorbital

Thisnumberreferstotheshapeoftheorbital.Thenumberofpossibleshapesislimitedbytheprincipalquantumnumber.Thefirstenergylevelhasonlyonepossibleshape,thesorbitalbecausen=1andthelimitof =(n−1)=0.Thesecondhastwopossibleshapes,thesandp.SeeFigures8aand8bforrepresentationsoftheseshapes.

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Theprincipalquantumnumberrefers

to theprincipalenergy level:1,2,3,and so on. The angular momentumquantumnumberreferstoshape.

Magneticquantumnumber( )s=1space-orientedorbitalp=3space-orientedorbitalsd=5space-orientedorbitalsf=7space-orientedorbitalsThevalueof canequal− ...0...+ .Spinquantumnumber(ms)+spin−spinThevalueofm=

ThedrawingsinFigure8ashowthes-orbitalshape,whichisasphere,andtheporbitals,whichhavedumbbellshapeswiththreepossibleorientationsontheaxisshown.Thenumberofspatialorientationsoforbitalsisreferredtoasthemagneticquantumnumber.Thepossibleorientationsarelisted.Figure8brepresentsthedorbitals.Electronsareassignedonemorequantumnumbercalledthespinquantumnumber.Thisdescribesthespinineitheroftwopossibledirections.Eachorbitalcanbefilledbyonlytwoelectronswithoppositespins.ThemainsignificanceofelectronspinisexplainedbythepostulateofWolfgangPauli.Itstatesthatinagivenatomnotwoelectronscanhavethesamesetoffourquantumnumbers(n, ,,andms).ThisisreferredtoasthePauli

ExclusionPrinciple.ThereforeeachorbitalinFigures8aand8bcanholdonlytwoelectrons.

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PauliExclusion Principle: No twoelectrons can have the same fourquantumnumbers.

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sorbitalsaresphericalandcanhold2electrons.

Two representations of the hydrogen 1s, 2s, and 3s orbitals. (1) The electronprobabilitydistribution; thenodes indicate regionsof zeroprobability. (2)Thesurfacethatcontains90%ofthetotalelectronprobability(thesizeoftheorbital,bydefinition).

Representationofthe2porbitals. (1)Theelectronprobabilitydistributionand(2)theboundarysurfacerepresentationsofallthreeorbitals.

FIGURE8a.Representationsofsandporbitals

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p orbitals have a dumbell shape,oriented on the x,y, and z axes, and

can hold a total of 2 electrons each,makingatotalof6.

(Indicatesorbitalsinyandzplanes)Representationsofthe3dorbitalsintermsoftheirboundarysurfaces.Thesubscriptsofthefirstfourorbitalsindicatetheplanesinwhichthefourlobesarecentered.

FIGURE8b.Representationsofdorbitals

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d orbitals have 5 orientations andcanhold2electronseach,makingatotalof10.

Quantumnumbersaresummarizedinthetablebelow.

Hund’sRuleofMaximumMultiplicityandtheAufbauPrincipleIt is important to remember that, when there is more than one orbital at aparticular energy level, such as three p orbitals or five d orbitals, only oneelectronwillfilleachorbitaluntileachhasoneelectron.Thisprinciple,thatanelectron occupies the lowest energy orbital that can receive it, is called theAufbauPrinciple.After this,pairingwilloccurwith theadditionofonemoreelectron to each orbital. This principle, called Hund’s Rule of MaximumMultiplicity,isshowninTable2,whereeacharrowheadindicatesanelectron().

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Know the Aufbau Principle andHund’s Rule of MaximumMultiplicity.

Ifeachorbitalisindicatedinanenergydiagramasasquare( ),wecanshowrelativeenergiesinachartsuchasFigure9.Ifthisdrawingrepresentedaravinewith the energy levels as ledgesontowhich stones could come to rest only innumbers equal to the squares for orbitals, then pushing stones into the ravinewould cause the stones to lose their potential energy as they dropped to thelowestpotentiallevelavailabletothem.Muchthesameistrueforelectrons.

SUBLEVELSANDELECTRONCONFIGURATION

OrderofFillingandNotationThe sublevels do not fill up in numerical order, and the pattern of filling isshownon therightsideof theapproximaterelativeenergylevelschart (Figure9).Inthefirstinstanceoffailuretofollownumericalorder,the4sfillsbeforethe3d.(StudyFigure9carefullybeforegoingon.)

Figure9.ApproximateRelativeEnergyLevelofSubshells

19K 1s22s22p63s23p64s1

20Ca 1s22s22p63s23p64s2

21Sc1s22s22p63s23p64s23d1(note4sfilledbefore3d)

There is amore stable configuration to a half-filled or filled sublevel, so atatomicnumber24the3dsublevelbecomeshalf-filledbytakinga4selectron;

24Cr 1s22s22p63s23p63d54s1

andatatomicnumber29the3dbecomesfilledbytakinga4selectron:

29Cu 1s22s22p63s23p63d104s1

Table3showstheelectronconfigurationsoftheelements.Atriangularmark indicates an outer-level electron dropping back to a lower unfilled orbital.

These phenomena are exceptions to the Aufbau Principle. By following theatomicnumbers throughout thischart,youwillget thesameorderoffillingasshowninFigure9.

Table3.ElectronConfigurationoftheElements

Note:Followorderoftheatomicnumberstoascertaintheorderoffilling.

ByfollowingtheatomicnumbersinnumericalorderinTable3youcanplottheorderoffillingoftheorbitalsforeveryelementshown.Asimplifiedmethodofshowingtheorderinwhichtheorbitalsarefilledisto

use the following diagram. It works for all the naturally occurring elementsthroughlanthanum,atomicnumber88.

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This is a simple way to remembertheorderoffillingorbitals.

Start by drawing the diagonal arrows through the diagram as shown. Theorder of filling can be charted by following each arrow from tail to head andthentothetailofthenextone.InthiswayyougetthesameorderoffillingasisshowninFigure9andTable3:

1s22s22p63s23p64s23d104p65s24d105p66s24f145d106p67s2

LewisStructures(ElectronDotNotation)In1916G.N.Lewis devised the electrondot notation,whichmaybeused inplace of the electron configuration notation. The electron dot notation showsonly the chemical symbol surroundedbydots to represent the electrons in theincompleteouterlevel.Examplesare:

Thesymboldenotesthenucleusandallelectronsexceptthevalenceelectrons.The dots are arranged at the four sides of the symbol and are paired whenappropriate. In the examples above, the depicted electrons are the valenceelectronsfoundintheouterenergylevelorbitals.

4s1isshownforpotassium(K)4s24p3areshownforarsenic(As)5s2isshownforstrontium(Sr)5s25p5areshownforiodine(I)6s26p6areshownforradon(Rn)

NobleGasNotationAnothermethodofsimplifyingtheelectrondistributiontotheorbitalsiscalledthe noble gas notation. In this method you represent all of the lower filledorbitals up to the closest noble gas. By enclosing its symbol in brackets, it

represents all of the complete noble gas configuration. Then the remainingorbitalsarewrittenintheusualway.Anexampleofthiscanbeshownbyusingthethirdperiodofelements.Byusingneonasthenoblegas,youwrite[Ne]torepresentitsorbitalstructure,whichis1s22s22p6.Thisallowsyoutowriteanelement like sodiumas [Ne]3s1,which is called sodium’s noble gas notation.The table in the next section shows the noble gas notations of some of thetransition elements in the fourth period of elements. Notice that the basestructureofargonisusedandrepresentedas[Ar].

TRANSITIONELEMENTSTheelements involvedwith the fillingofad sublevelwithelectronsafter twoelectronsareinthessublevelofthenextprincipalenergylevelareoftenreferredto as the transition elements. The first examples of these are the elementsbetween calcium, atomic number 20, and gallium, atomic number 31. Theirelectronconfigurationsarethesameinthe1s,2s,2p,3s,and3psublevels.It isthefillingofthe3dandchangesinthe4ssublevelsthatareofinterest,asshowninthefollowingtable.

Theasterisk(*)showswherea4selectronispromotedintothe3d sublevel.Thisisbecausethe3dand4ssublevelsareverycloseinenergyandthatthereisastateofgreaterstabilityinhalf-filledandfilledsublevels.Therefore,chromiumgainsstabilitybythemovementofanelectronfromthe4ssublevelintothe3dsubleveltogiveahalf-filled3dsublevel.Itthenhasoneelectronineachofthefiveorbitalsofthe3dsublevel.Incopper,themovementofone4selectroninto

the3dsublevelgivesthe3dsublevelacompletelyfilledconfiguration.The fact that theelectrons in the3dand4s sublevels are soclose in energy

levels leads to thepossibilityofsomeorall the3delectronsbeing involved inchemicalbonding.Withthevariablenumberofelectronsavailableforbonding,it is not surprising that transition elements can exhibit variable oxidationnumbers.Anexampleismanganesewithpossibleoxidationnumbersof+2,+3,+4,+6,and+7,whichcorrespond,respectively,totheuseofno,one,two,four,andfiveelectronsfromthe3dsublevel.Thetransitionelementsintheotherperiodsofthetableshowthissametype

ofanomaly,astheyhavedsublevelsfillinginthesamemanner.Transitionelementshaveseveralcommoncharacteristicproperties.

•Theyoftenformcoloredcompounds.

•Theycanhaveavarietyofoxidationstates.

•Atleastoneoftheircompoundshasanincompletedelectronsubshell.

•Theyareoftengoodcatalysts.

•Theyaresilveryblueatroomtemperature(exceptcopperandgold).

•Theyaresolidsatroomtemperature(exceptmercury).

•Theyformcomplexions.

•Theyareoftenparamagnetic.

PERIODICTABLEOFTHEELEMENTS

HistoryThehistoryofthedevelopmentofasystematicpatternfortheelementsincludesthe work of a number of scientists such as John Newlands, who, in 1863,proposedtheideaofrepeatingoctavesofproperties.DimitriI.Mendeleevin1869proposedatablecontaining17columnsandis

usually given credit for the first periodic table since he arranged elements ingroupsaccordingtotheiratomicweightsandproperties.ItisinterestingtonotethatLotharMeyerproposedasimilararrangementaboutthesametime.In1871Mendeleev rearranged some elements and proposed a table of eight columns,obtained by splitting each of the long periods across into a period of seven

elements,aneighthgroupcontainingthethreecentralelements(suchasFe,Co,Ni), and a second period of seven elements. The first and second periods ofsevenacrosswere laterdistinguishedbyuseof the lettersAandBattached tothegroupsymbols,whichwereRomannumerals.Thisnomenclatureofperiods(IA, IIA, etc.) has been revised in the present Periodic Table, even in theextendedformofassigningArabicnumbersfrom1–18asshowninTable4.

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Mendeleev is given credit for thefirstPeriodicTable.Itwasbasedonplacementbyproperties.

Table4.PeriodicTableProperties

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Periodsarethehorizontalrows1–7.Groups are the vertical columns 1–18.

Mendeleev’s table had the elements arranged by atomic weights withrecurring properties in a periodic manner. Where atomic weight placementdisagreedwiththepropertiesthatshouldoccurinaparticularspotinthetable,Mendeleevgavepreferencetotheelementwiththecorrectproperties.Heevenpredicted elements for places that were not yet occupied in the table. Thesepredictionsproved tobeamazinglyaccurateand led towideacceptanceofhistable.

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Knowtheserelationshipsacross thetable.

PeriodicLawHenryMoseleystated,afterhisworkwithx-rayspectraintheearly1900s,thatthepropertiesofelementsareaperiodicfunctionoftheiratomicnumbers,thuschanging the basis of the periodic law from atomicweight to atomic number.Thisisthepresentstatementoftheperiodiclaw.

TheTableThehorizontalrowsoftheperiodictablearecalledperiodsorrows.Thereareseven periods, each of which begins with an atom having only one valenceelectronandendswithacompleteoutershellstructureofaninertgas.Thefirstthreeperiodsareshort,consistingof2,8,and8elements,respectively.Periods4and5arelonger,with18each,whileperiod6has32elements,andperiod7isincompletewith22elements,mostofwhichareradioactiveanddonotoccurinnature.

InTable4,youshouldnotetherelationshipofthelengthoftheperiodstotheorbitalstructureoftheelements.Inthefirstperiod,the1s2orbitalisfilledwiththenoblegashelium,He.Thesecondperiodbeginswiththe2s1orbitalandendswith thefillingof the2p6orbital, againwithanoblegas,neon,Ne.Thesamepattern is repeated in period three, going from3s1 to 3p6. The eight elementsfromsodium,Na,toargon,Ar,completethefillingofthen=3energylevelwith3s2 and 3p6. In the fourth period, the first two elements fill the 4s2 orbital.Beyondcalcium,Ca,thepatternbecomesmorecomplicated.Asdiscussedinthesection“OrderofFillingandNotation,”thenextorbitalstobefilledarethefive3d orbitals whose elements represent transition elements. Then the three 4porbitals are filled, ending with the noble gas krypton, Kr. The fifth period issimilar to the fourthperiod.The5s2 orbital filling is representedby rubidium,Rb,andstrontium,Sr,bothofwhichresembletheelementsdirectlyabovethemon the table. Next come the transition elements that fill the five 4d orbitalsbeforethenextgroupofelements,fromindium,In,toxenon,Xe,completethethree5porbitals.(Table3shouldbeconsultedfortheirregularitiesthatoccurasthedorbitalsfill.)Thesixthperiodfollowsmuchthesamepatternandhasthefillingorder6s2,4f14,5d10,6p6.Here,again,irregularitiesoccurandcanbestbefollowedbyusingTable3.TheverticalcolumnsofthePeriodicTablearecalledgroupsorfamilies.The

elements in a group exhibit similar or related properties. In 1984 the IUPACagreedthatthegroupswouldbenumbered1through18.

PROPERTIESRELATEDTOTHEPERIODICTABLEMetalsarefoundontheleftofthechart(seeTable4)withthemostactivemetalin the lower left corner.Nonmetals are found on the right sidewith themostactivenonmetalintheupperright-handcorner.Thenobleorinertgasesareonthe far right. Since themost activemetals reactwithwater to formbases, theGroup1metalsarecalledalkalimetals.Asyouproceed to theright, thebase-formingpropertydecreasesandtheacid-formingpropertiesincrease.Themetalsinthefirsttwogroupsarethelightmetals,andthosetowardthecenterareheavymetals.The elements found along the dark line in the Periodic Table (Table 4) are

calledmetalloids. These elements have certain characteristics of metals and

other characteristics of nonmetals. Some examples of metalloids are boron,silicon,arsenic,andtellurium.Here are some important general summary statements about the Periodic

Table:

•Acid-formingpropertiesincreasefromlefttorightonthetable.

•Base-formingpropertiesarehighontheleftsideanddecreasetotheright.

•Theatomicradiiofelementsdecreasefromlefttorightacrossaperiod.

•Firstionizationenergiesincreasefromlefttorightacrossaperiod.

•Metallicpropertiesaregreatestontheleftsideofthetableanddecreasetotheright.

•Nonmetallicpropertiesaregreatestontherightsideofthetableanddecreasetotheleft.

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These are important trends toremember.

StudyTable4carefullybecauseitsummarizesmanyoftheseproperties.Foramoredetaileddescriptionofmetals,alloys,andmetalloidsseeChapter13.

RadiiofAtomsThesizeofanatomisdifficulttodescribebecauseatomshavenodefiniteouterboundary.Unlikeavolleyball,anatomdoesnothaveadefinitecircumference.Toovercomethisproblem,thesizeofanatomisestimatedbydescribingits

radius.Inmetals, thisisdonebymeasuringthedistancebetweentwonucleiinthesolidstateanddividingthisdistanceby2.Suchmeasurementscanbemadewith xray diffraction. For a nonmetallic element that exists in pure form as amolecule,suchaschlorine,measurementscanbemadeofthedistancebetweennucleifortwoatomscovalentlybondedtogether.Halfofthisdistanceisreferredto as the covalent radius. Themethod for finding the covalent radius of thechlorineatomisillustratedinthefollowingdiagram.

Figure10shows the relativeatomicand ionic radii for someelements.Asyoureviewthischart,youshouldnotetwotrends:

1.AtomicradiidecreasefromlefttorightacrossaperiodinthePeriodicTable(untilthenoblegases).

2.Atomicradiiincreasefromtoptobottominagrouporfamily.

Thereasonforthesetrendswillbecomeclearinthefollowingdiscussions.

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Knowthesetrendsinatomicradii.

AtomicRadiiinPeriodsSincethenumberofelectronsintheouterprincipalenergylevelincreasesasyougo from left to right in each period, the corresponding increase in the nuclearchargebecauseoftheadditionalprotonspullstheelectronsmoretightlyaroundthenucleus.Thisattractionmorethanbalancestherepulsionbetweentheaddedelectronsandtheotherelectrons,andtheradiusisgenerallyreduced.Theinertgasattheendoftheperiodhasaslightincreaseinradiusbecauseoftheelectronrepulsioninthefilledouterprincipalenergylevel.Forexample,lithium’satomicradiusinFigure10is0.152nmattheoneendofperiod2whereasfluorinehasaradiusofonly0.064nmat thefarendof theperiod.This trendcanbeseeninFigure10acrosseveryperiod.

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Thisistheexplanationofthesetrendsinperiods.

AtomicRadiiinGroupsFor a group of elements, the atoms of each successivemember have anotherouterprincipalenergylevelintheelectronconfigurationandtheelectronsthereareheldlesstightlybythenucleus.Thisissobecauseoftheirincreaseddistancefromthenuclearpositivechargeandtheshieldingofthispositivechargebyallthe core electrons. Therefore the atomic radius increases down a group. Forexample,oxygen’satomicradiusinFigure10is0.066nmatthetopofgroup16,whereas poloniumhas a radius of 0.167nmat the bottomof the samegroup.ThistrendcanbeseeninFigure10downeverygroup.

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...andingroups.

IonicRadiusComparedwithAtomicRadiusMetalstendtoloseelectronsinformingpositiveions.Withthislossofnegativecharge, the positive nuclear charge pulls in the remaining electrons closer andthusreducestheionicradiusbelowthatoftheatomicradius.Nonmetals tend to gain electrons in forming negative ions.With this added

negativecharge,whichincreasestheinnerelectronrepulsion,theionicradiusisincreasedbeyondtheatomicradius.SeeFigure10forrelativeatomicandionicradiivalues.

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Know this relationship between theatomicradiusandtheionicradius.

FIGURE10.RadiiofSomeAtomsandIons(innanometers)

Notes:Theatomicradiusisusuallygivenformetalatoms,whichareshowningray,andthecovalentradiusisusuallygivenforatomsofnonmetals,whichareshowninblack.

ElectronegativityThe electronegativity of an element is a number that measures the relative

strength with which the atoms of the element attract valence electrons in achemical bond. This electronegativity number is based on an arbitrary scalegoingfrom0to4.Ingeneral,avalueoflessthan2indicatesametal.Notice in Table 5 that the electronegativity decreases down a group and

increases across a period. The inert gases can be ignored. The lower theelectronegativitynumber,themoreelectropositiveanelementissaidtobe.Themostelectronegativeelementisintheupperrightcorner—F,fluorine.Themostelectropositiveisinthelowerleftcornerofthechart—Fr,francium.

Table5.FirstIonizationEnergiesandElectronegativities

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ThemostelectronegativeelementisF,intheupperrightcorner.

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The leastelectronegativeelement isFr,inthelowerleftcorner.

IonizationEnergyAtoms hold their valence electrons, then,with different amounts of energy. Ifenoughenergyissuppliedtooneouterelectrontoremoveitfromitsatom,thisamount of energy is called the first ionization energy.With the first electrongone,theremovalofsucceedingelectronsbecomesmoredifficultbecauseoftheimbalancebetweenthepositivenuclearchargeandtheremainingelectrons.Thelowestionizationenergyisfoundwiththeleastelectronegativeatom.

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Know this definition of the firstionizationenergy.

Ionization energies can be plotted against atomic numbers, as shown in thegraph below. Follow this discussion on the graph to help you understand thepeaksandvalleys.Notsurprisingly,thehighestpeaksonthegraphoccurfortheionizationenergyneededtoremovethefirstelectronfromtheouterenergylevelof thenoblegases,He,Ne,Ar,Kr,Xe,andRn,becauseof thestabilityof thefilled p orbitals in the outer energy level. Notice that, even among theseelements, the energy needed gradually declines. This can be explained byconsideringthedistanceoftheinvolvedenergylevelfromthepositivelychargednucleus.With each succeedingnoblegas, amoredistantp orbital is involved,thereforemakingiteasier toremoveanelectronfromthepositiveattractionofthenucleus.Besides thisconsideration,asmoreenergy levelsareadded to theatomic structure as the atomicnumber increases, the additionalnegative fieldsassociatedwiththeadditionalelectronsscreenoutsomeofthepositiveattractionofthenucleus.WithinaperiodsuchasthatfromLitoNe,theionizationenergygenerallyincreases.Thelowestoccurswhenaloneelectronoccupiestheoutersorbital,asinLi.Asthesorbitalfillswithtwoelectronsatatomicnumber4,Be,theaddedstabilityofafilled2sorbitalexplainsthesmallpeakat4.Atatomic

number 5, B, a lone electron occupies the 2p orbital. This electron can beremovedwithlessenergy,andthereforeadipoccursinthegraph.Withthe2porbitals filling according to Hund’s Rule (refer to Table 2), with only oneelectron in each orbital before pairing occurs, again a slightly more stablesituationand,therefore,anothersmallpeakoccuratatomicnumber7.Afterthispeak, a dip and continual increases occur until the 2p orbitals are completelyfilledwithpairedelectronsatthenoblegasNe.Asyoucontinuetoassociatetheatomicnumberwiththelineinthechart,youfindpeaksoccurringinthesamegeneral pattern. These peaks are always related to the state of filling of theorbitalsinvolvedandthedistanceoftheseorbitalsfromthenucleus.

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Know how this trend relates to thechart.Canyouexplainthepeaks?

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Know the reason for the peaks andvalleys.

NUCLEARTRANSFORMATIONSANDSTABILITYAt the same time advances in atomic theory were occurring, scientists werenoticingphenomenaassociatedwithemissionsfromthenucleusofatomsintheform of “X-rays.” While Roentgen announced the discovery of X-rays,Becquerel was exploring the phosphorescence of some materials. Becquerel’swork received littleattentionuntilearly in1898,whenMarieandPierreCurieenteredthepicture.Searchingforthesourceoftheintenseradiationinuraniumore,MarieandPierreCurieusedtonsofittoisolateverysmallquantitiesoftwonew elements, radium and polonium, both radioactive.AlongwithBecquerel,theCuriessharedtheNobelPrizeinphysicsin1903.

THENATUREOFRADIOACTIVEEMISSIONSWhiletheearlyseparationexperimentswereinprogress,anunderstandingwasslowlybeinggainedofthenatureofthespontaneousemissionfromthevariousradioactiveelements.Becquerel thought at first that therewere simplyX-rays,butTHREEdifferentkindsofradioactiveemission,nowcalledalphaparticles,betaparticles, andgamma rays, were soon found.We now know that alphaparticles are positively charged particles of helium nuclei, beta particles arestreams of high-speed electrons, and gamma rays are high-energy radiationssimilar to X-rays. The emission of these three types of radiation is depictedbelow.

The important characteristics of each type of radiation can be summarized asfollows:

AlphaParticle((heliumnucleus )Positivelycharged,2+1.Ejectionreducestheatomicnumberby2,theatomicweightby4amu.2.Highenergy,relativevelocity.3.Range:about5cminair.4.Shieldingneeded:stoppedbythethicknessofasheetofpaper,skin.5.Interactions:producesabout100,000ionizationspercentimeter;repelledbythepositivelychargednucleus;attractselectrons,butdoesnotcapturethemuntilitsspeedismuchreduced.

6.Anexample:Thorium-230hasanunstablenucleusandundergoesradioactivedecaythroughalphaemission.Thenuclearequationthatdescribesthisreactionis:

Inadecayreactionlikethis,theinitialelement(thorium-230)iscalledtheparentnuclideandtheresultingelement(radium-226)iscalledthedaughternuclide.

BetaParticle(fastelectron)Negativelycharged,1−1.Ejectedwhenaneutrondecaysintoaprotonandanelectron.2.Highvelocity,lowenergy.3.Range:about12m.4.Shieldingneeded:stoppedby1cmofaluminumorthicknessofaveragebook.

5.Interactions:weakbecauseofhighvelocity,butproducesabout100ionizationspercentimeter.

6.Anexample:Protactinium-234isaradioactivenuclidethatundergoesbetaemission.Thenuclearequationis:

GammaRadiation(electromagneticradiationidenticalwithlight;highenergy)Nocharge

1.Betaparticlesandgammaraysareusuallyemittedtogether;afterabetaisemitted,agammarayfollows.

2.Arrangementinnucleusisunknown.Samevelocityasvisiblelight.3.Range:nospecificrange.4.Shieldingneeded:about13cmoflead.5.Interactions:weakofitself;givesenergytoelectrons,whichthenperformtheionization.

METHODSOFDETECTIONOFALPHA,BETA,ANDGAMMARAYSAllmethodsofdetectionoftheseradiationsrelyontheirabilitytoionize.Threemethodsareincommonuse.

1.Photographicplate.Thefoggingofaphotographicemulsionledtothediscoveryofradioactivity.Ifthisemulsionisviewedunderahigh-powermicroscope,itisseenthatbetaandgammarayscausethesilverbromidegrainstodevelopinascatteredfashion.

2.Scintillationcounter.Afluorescentscreen(e.g.,ZnS)willshowthe

presenceofelectronsandX-rays,asalreadymentioned.Ifthescreenisviewedwithamagnifyingeyepiece,smallflashesoflight,calledscintillations,willbeobserved.Byobservingthescintillations,onenotonlycandetectthepresenceofalphaparticles,butalsocanactuallycountthem.

3.Geigercounter.Thisinstrumentisperhapsthemostwidelyusedatthepresenttimefordeterminingindividualradiation.Anyparticlethatwillproduceaniongivesrisetoanavalancheofions,sothetypeofparticlecannotbeidentified.However,eachindividualparticlecanbedetected.

DECAYSERIES,TRANSMUTATIONS,ANDHALF-LIFEThenuclei of uranium, radium, and other radioactive elements are continuallydisintegrating.Itshouldbeemphasizedthatspontaneousdisintegrationproducesthegasknownasradon.Thetimerequiredforhalfoftheatomsofaradioactivenuclidetodecayiscalleditshalf-life.

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Know how to use half-life todeterminetheageofasubstance.

See “Radioactive Dating” for moreinfo.

Forexample,forradium,weknowthat,ontheaverage,halfofalltheradiumnucleipresentwillhavedisintegratedtoradonin1,590years.Inanother1,590years, half of this remainder will decay, and so on. When a radium atomdisintegrates, it loses an alpha particle, which eventually, upon gaining twoelectrons,becomesaneutralheliumatom.Theremainderoftheatombecomesradon.Suchaconversionofanelementtoanewelement(becauseofachangeinthe

number of protons) is called a transmutation. This transmutation can beproduced artificially by bombarding the nuclei of a substance with variousparticlesfromaparticleaccelerator,suchasthecyclotron.Thefollowinguranium-radiumdisintegrationseriesshowshowaradioactive

atom may change when it loses each kind of particle. Note that an atomicnumber is shownby a subscript (92U), and the isotopicmass by a superscript(238U).The alpha particle is represented by theGreek symbolα, and the betaparticlebyβ.

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Know how each type of emissionaffects the atomic mass and theatomicnumber.

The changes that occur in radioactive reactions and the subatomic particlesinvolvedaresummarizedinthefollowingcharts.

Thisisshowngraphicallyintheradioactivedecayseriesbelow.

RADIOACTIVEDATINGAhelpfulapplicationofradioactivedecayisinthedeterminationoftheagesofsubstancessuchasrocksandrelicsthathavebitsoforganicmaterialtrappedinthem.Becausecarbon-14hasahalf-lifeofabout5,700yearsandoccursintheremainsoforganicmaterials,ithasbeenusefulindatingthesematerials.AsmallpercentageofCO2in theatmospherecontainscarbon-14.Thestable isotopeofcarboniscarbon-12.Carbon-14isabetaemitteranddecaystoformnitrogen-14:

Inanylivingorganism,theratioofcarbon-14tocarbon-12isthesameasinthe atmosphere because of the constant interchange of materials betweenorganismandsurroundings.Whenanorganismdies, this interactionstops,andthecarbon-14graduallydecaystonitrogen.Bycomparingtherelativeamountsof carbon-14 and carbon-12 in the remains, the age of the organism can beestablished.Carbon-14hasahalf-lifeof5,700years. Ifa sampleofwoodhadoriginallycontained5gramsofcarbon-14andnowhadonlyhalfor2.5gramsofcarbon-14,itsagewouldbe5,700years.Inotherwords,theoldwoodemitshalfasmuchbetaradiationpergramofcarbonasthatemittedbylivingplanttissues.ThismethodwasusedtodeterminetheageoftheDeadSeaScrolls(about1,900years) and has been found to be in agreement with several other datingtechniques.

NUCLEARREACTIONSNuclear fission reactions have been in use since the 1940s. The first atomicbombs used in 1945 were nuclear fission bombs. Since that time, manycountries, includingourown,haveputnuclearfissionpowerplants intouse toprovide a new energy source for electrical energy.Basically, a nuclear fissionreactionisthesplittingofaheavynucleusintotwoormorelighternuclei.

EXAMPLE:U-235isbombardedwithslowneutronstoproduceBa-139,Kr-94,orotherisotopesandalso3fast-movingneutrons.

A nuclear chain reaction is a reaction in which an initial step, such as thereaction above, leads to a succession of repeating steps that continuesindefinitely. Nuclear chain reactions are used in nuclear reactors and nuclearbombs.Anuclearfusionreaction is thecombinationofverylightnuclei tomakea

heaviernucleus.Extremelyhightemperaturesandpressuresarerequiredinorderto overcome the repulsive forces of the two nuclei. Fusion has been achievedonly in hydrogen bombs. Scientists are still trying to harness this reaction fordomesticuses.Thefollowingexamplesshowbasicallyhowthereactionsoccur.

EXAMPLES:Twodeuteriumatomscombining

Tritiumcombiningwithhydrogen

Theenergyreleased inanuclearreaction(eitherfissionorfusion)comesfromthe fractional amount ofmass converted into energy.Nuclear changes convertmatterintoenergy.Energyreleasedduringnuclearreactionsismuchgreaterthantheenergyreleasedduringchemicalreactions.

ChapterSummaryThefollowingtermssummarizealltheconceptsandideasthatwereintroducedinthischapter.Youshouldbeabletoexplaintheirmeaningandhowyouwouldusetheminchemistry.Theyappearinboldfacetypeinthischaptertodrawyourattentiontothem.Theboldfacetypealsomakesiteasierforyoutolookthemupif you need to. You could also use the search or “Google” action on yourcomputer to get a quick and expanded explanation of these terms, laws, andformulas.

alphaparticle half-life oxidationnumberatomicmass Hund’sRule PauliExclusionPrincipleatomicnumber inertatoms periodiclawatomicradii ionicradii periodorrowAufbauPrinciple ionizationenergy phosphorescencebetaparticle isotopes quantumnumbersBohrmodel Lewisstructure quantumtheorycovalentradius Mendeleev radonDalton’satomictheory metalloids s,p,d,forbitalselectron Moseley transmutationelectronegativity neutron transitionelementsgammaray nuclearfission uncertaintyprincipleGeigercounter nuclearfusion valenceelectronsgrouporfamily nucleus wave-mechanicalmodel

InternetResourcesOnlinecontent that reinforces themajorconceptsdiscussed in thischaptercanbefoundatthefollowingInternetaddressesiftheyarestillavailable.Somemayhavebeenchangedordeleted.EmissionSpectroscopyhttp://phys.educ.ksu.edu/vqm/html/emission.htmlThis site offers interactive computer visualizations of the quantum effects of

emissionspectraforavarietyofsubstances.InteractivePeriodicTablehttp://www.webelements.comThisisaninteractiveonlineperiodictableavailableontheWeb.www.ptable.com/Thissiteshowsproperties,orbitals,andisotopesinchartform.RadioactiveDatinghttp://chemistry.about.com/od/workedchemistryproblems/a/c14dating.htmThisWebpageoffersatutorialonradioactivedatingusingcarbon-14.

PracticeExercises1.Thetwomainregionsofanatomarethe

(A)principalenergylevelsandenergysublevels(B)nucleusandkernel(C)nucleusandenergylevels(D)planetaryelectronsandenergylevels

2.Thelowestprincipalquantumnumberthatanelectroncanhaveis

(A)0(B)1(C)2(D)3

3.Thesublevelthathasonlyoneorbitalisidentifiedbytheletter

(A)s(B)p(C)d(D)f

4.Thesublevelthatcanbeoccupiedbyamaximumof10electronsisidentifiedbytheletter

(A)d(B)f

(C)p(D)s

5.Anorbitalmayneverbeoccupiedby

(A)1electron(B)2electrons(C)3electrons(D)0electrons

6.Anatomofberylliumconsistsof4protons,5neutrons,and4electrons.Themassnumberofthisatomis

(A)13(B)9(C)8(D)5

7.Thenumberoforbitalsinthesecondprincipalenergylevel,n=2,ofanatomis

(A)1(B)9(C)16(D)4

8.Lewisstructureconsistsofthesymbolrepresentingtheelementandanarrangementofdotsthatusuallyshows

(A)theatomicnumber(B)theatomicmass(C)thenumberofneutrons(D)theelectronsintheoutermostenergylevel

9.ChlorineisrepresentedbytheLewisstructure .Theatomthatwouldberepresentedbyanidenticalelectron-dotarrangementhastheatomicnumber

(A)7(B)9(C)15(D)19

10.Radioactivechangesdifferfromordinarychemicalchangesbecauseradioactivechanges

(A)involvechangesinthenucleus(B)areexplosive(C)absorbenergy(D)releaseenergy

11.Isotopesofuraniumhavedifferent

(A)atomicnumbers(B)atomicmasses(C)numbersofplanetaryelectrons(D)numbersofprotons

12.Atomsof235Uand238Udifferinstructurebythree

(A)electrons(B)isotopes(C)neutrons(D)protons

13.Theuseofradioactiveisotopeshasproducedpromisingresultsinthetreatmentofcertaintypesof

(A)cancer(B)heartdisease(C)pneumonia(D)diabetes

14.Theemissionofabetaparticleresultsinanewelementwiththeatomicnumber

(A)increasedby1(B)increasedby2(C)decreasedby1(D)decreasedby2

ThefollowingquestionsareintheformatthatisusedontheSATSubjectTestinChemistry.

Questions15–19Usethisabbreviatedperiodictabletoanswerthefollowingquestions.

15.Whichneutralatomhasanouterenergylevelconfigurationof3s1?

16.Anatomofwhichelementshowsthegreatestaffinityforanadditionalelectron?

17.Whichelementisthemostactivemetalofthisgroup?

18.Whichelementhasthelowestelectronegativityofthisgroup?

19.Whichelementhasanouterorbitalconfigurationof2s22p2?

Directions:

Every question below contains two statements, I in the left-hand columnandIIintheright-handcolumn.Foreachquestion,decideifstatementIistrue or false and whether statement II is true or false, and fill in thecorrespondingTorFovals in theanswerspaces.*Fill inovalCEonly ifstatementIIisacorrectexplanationofstatementI.

I II20.Si,withanatomic

numberof14,willprobablyexhibitanoxidationnumberof+4inacompound

BECAUSE siliconisanelementthathasamphotericproperties.

21.Nonmetallicatomshavelargerionicradiithantheiratomicradii

BECAUSE

nonmetallicatomsgenerallygainelectronstoformtheionicstateandincreasethesizeoftheelectroncloud.

22.ElementsintheupperrightcornerofthePeriodicTableformacidanhydrides

BECAUSEnonmetallicoxidesreactwithwatertoformacidsolutions.

*FillinovalCEonlyifIIisacorrectexplanationofI.

AnswersandExplanations1.(C)Thetwomainpartsoftheatomarethenucleusanditsenergylevels.

2.(B)Theprincipalquantumnumbersstartwiththevalueof1torepresentthefirstlevel.

3.(A)Thelettersisusedtorepresentthefirstorbitalthatcanholdtwoelectrons.

4.(A)Thesubleveldhasfiveorbitalsthateachcanholdtwoelectrons,totalingtenelectrons.

5.(C)Eachorbitalcanonlyholdtwoelectrons.

6.(B)Themassnumberisthetotalofthenumberofprotonsandneutrons,whichinthiscaseisnine.

7.(D)Thesecondprincipalenergylevelhasansorbitalandthreeporbitals,makingatotaloffour.

8.(D)TheLewiselectron-dotnotationshowsthesymbolandtheoutermostenergy-levelelectrons,whicharereferredtoasthevalenceelectrons.

9.(B)Chlorineisamemberofthehalogenfamilyfoundingroup17.Theotherelementinthesamefamilywouldbetheelementwiththeatomicnumber9,fluorine.

10.(A)Radioactivechangesdifferbecausetheyinvolvechangesinthenucleus.

11.(B)Isotopesdifferintheiratomicmassbecauseofdifferencesinthenumberofneutrons.

12.(C)Thesetwoisotopes,235Uand238U,differintheiratomicmassby3neutrons.

13.(A)Radioactiveisotopeshavebeensuccessfulinthetreatmentofcertaincancers.

14.(A)Abetaparticleemissioncausesanincreaseof1intheatomicnumber.

15.(B)BecauseNa(sodium)hasthepositionshown,ithastheatomicnumber11.Theelectronconfigurationis1s22s22p63s1.

16.(E)Fluorinehassevenelectronsinitsouterenergylevelandneedsonlyonemoretocompleteitsouterenergyleveloctet.Itthereforehasthegreatestaffinityforonemoreelectron.

17.(C)Themostactivemetalofthegroupisfoundinthelowerleft-handcorner.Becauseitsouterenergylevelisfurthestfromthenucleusandthesearethemostlooselyheldelectrons,itisthemostlikelytoloseanelectron.

18.(C)Theelementthathasthelowestelectronegativitywillbeinthelowerleftcorner.Forthisgroup,itisK.

19.(D)Theelementthathasthisconfigurationiscarbon,whichhassixelectrons.Thefirsttwoareinthefirstlevel,andthenextfourareinthesecondlevel,as2s22p2.

20.(T,T)Bothstatementsaretrue,butstatementIIdoesnotexplainstatementI.

21.(T,T,CE)Becausenonmetallicatomsgainelectronstoformions,theadditionalnegativechargeoftheaddedelectronsincreasesthesizeoftheion.Thisoccursbecauseoftheincreasedrepulsionoftheadditionalnegativecharge(s)andadditionalshieldingfromthepositivelychargednucleus.

22.(T,T,CE)ElementsfoundintheupperrightcornerofthePeriodicTablearenonmetalsthatformoxidesandreactwithwatertoformacids.Anexampleissulfurthatformssulfurtrioxide,andthisreactswithwatertoformsulfuricacid.

CHAPTER3

Bonding

These are the skills that are usually tested on the SAT Subject Test inChemistry.Youshouldbeableto…•Defineionicandcovalentbonds,andexplainhowtheyform.•Identifythedifferencesinthecontinuumthatexistsbetweenionicandcovalentbonding.

•Describetheimplicationsofthetypeofbondonthestructureofthecompound.

•ExplaintheimplicationsofintermolecularforcesandvanderWaalsforces.•ExplainhowVSEPRandhybridizationsolvetheneedtocomplywithknownmolecularshapes.

This chapter will review and strengthen these skills. Be sure to do thePracticeExercisesattheendofthechapter.

Some elements show no tendency to combinewith either like atoms or otherkindsofelements.Theseelementsaresaid tobemonoatomicmolecules; threeexamples are helium, neon, and argon. Amolecule is defined as the smallestparticle of an element or a compound that retains the characteristics of theoriginalsubstance.Waterisatriatomicmoleculesincetwohydrogenatomsandone oxygen atom must combine to form the substance water with itscharacteristicproperties.When atoms do combine to form molecules, there is a shifting of valence

electrons, that is, theelectronsin theouterenergylevelofeachatom.Usually,this results in completion of the outer energy level of each atom. This morestable formmaybeachievedby thegainor lossofelectronsor the sharingofpairs of electrons. The resulting attraction of the atoms involved is called achemical bond. When a chemical bond forms, energy is released; when thisbondisbroken,energyisabsorbed.Thisrelationshipofbondingtothevalenceelectronsofatomscanbefurther

explainedbystudyingtheelectronstructuresoftheatomsinvolved.Asalready

mentioned,thenoblegasesaremonoatomicmolecules.Thereasoncanbeseenintheelectrondistributionsofthesenoblegasesasshowninthefollowingtable.

The distinguishing factor in these very stable configurations is thearrangementoftwoselectronsandsixpelectronsinthevalenceenergylevelinfiveofthesixatoms.(Notethathelium,He,hasonlyasinglesvalenceenergylevel,which is filledwith two electrons,makingHe avery stable atom.)Thisarrangement is called a stableoctet. All other elements, other than the noblegases,haveone tosevenelectrons in theirouterenergy levels.Theseelementsare reactive to varying degrees.When they do react to form chemical bonds,usuallytheelectronsshiftinsuchawaythatstableoctetsform.Inotherwords,inbondformation,atomsusuallyattainthestableelectronstructureofoneofthenoblegases.Thetypeofbondformedisdirectlyrelatedtowhetherthisstructureisachievedbygaining,losing,orsharingelectrons.

Notice the reccurrence of the octet(8)ofelectronsinnoblegases.

TYPESOFBONDS

IonicBondsWhentheelectronegativityvaluesof twokindsofatomsdifferby1.7ormore(especially differences greater than 1.7), the more electronegative atom willborrowtheelectronsitneedstofillitsenergylevel,andtheotheratomwilllendelectronsuntilit,too,hasacompleteenergylevel.Becauseofthisexchange,the

borrowerbecomesnegativelychargedandiscalledananion;thelenderbecomespositivelychargedandiscalledacation.Theyarenowreferredtoasions,andthebondorattractionbetweenthemiscalledanionicbond.Theseionsdonotretainthepropertiesoftheoriginalatoms.AnexamplecanbeseeninFigure11.

A 1.7 or greater electronegativitydifference between atoms willessentiallyformanionicbond.

Theseionsdonotformanindividualmoleculeintheliquidorsolidphasebutare arranged into a crystal lattice or giant ion-molecule containingmany suchions. Ionic solids of this type tend to have high melting points and will notconductacurrentofelectricityuntiltheyareinthemoltenstate.

Figure11.TwoRepresentationsoftheIonicBondingofLiF

CovalentBondsWhen theelectronegativitydifferencebetween twoormoreatoms is0orverysmall(notgreaterthanabout0.4),theatomstendtosharethevalenceelectronsin their respective outer energy levels. This attraction is called a nonpolarcovalent bond. Here is an example using electron-dot notation and orbitalnotation:

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Covalent bonds involve a sharing ofelectrons between atoms. Theirelectronegativity difference isbetween0to0.5.

Thesecovalentbondedmoleculesdonothaveelectrostaticchargeslikethoseof ionic bonded substances. In general, covalent compounds are gases, liquidshaving fairly low boiling points, or solids that melt at relatively lowtemperatures.Unlikeioniccompounds,theydonotconductelectriccurrents.Whentheelectronegativitydifferenceisbetween0.4and1.6,therewillnotbe

anequalsharingofelectronsbetweentheatomsinvolved.Thesharedelectronswillbemore stronglyattracted to theatomofgreaterelectronegativity.As thedifferenceintheelectronegativitiesofthetwoelementsincreasesabove0.4,thepolarityordegreeofioniccharacterincreases.Atadifferenceof1.7ormore,thebond has more than 50% ionic character. However, when the difference isbetween0.4and1.6,thebondiscalledapolarcovalentbond.Anexample:

Notice that the electron pair in the bond is shown closer to the moreelectronegative atom. When these nonsymmetrical polar bonds are placedaroundacentralatom,theoverallmoleculeispolar.Intheexamplesabove,thechlorine (inHCl)andoxygen (inH2O)are considered thecentral atoms.Boththebondsand themolecules couldbedescribedaspolar.Polarmolecules arealso referred to asdipoles because thewholemolecule itself has two distinctendsfromachargeperspective.Becauseofthisunequalsharing,themoleculesshownaresaidtobepolarmolecules,ordipoles.However,polarcovalentbonds

exist in some nonpolar molecules. Examples are CO2, CH4, and CCl4. (SeeFigure12.)

Figure12.PolarCovalentBondsinNonpolarMolecules

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Polar covalent bonds have unequalsharing of electrons. Theirelectronegativity difference isbetween0.4and1.6.

Inall theexamples inFigure12 thebondsarepolarcovalentbonds,but theimportant thing is that they are symmetrically arranged in the molecule. Theresultisanonpolarmolecule.Inthecovalentbondsdescribedsofar, thesharedelectrons in thepairwere

contributed one each from the atoms bonded. In some cases, however, bothelectrons for the shared pair are supplied by only one of the atoms. TwoexamplesarethebondsinNH4+andH2SO4.(SeeFigure13.)

Figure13.CovalentBonds(bothelectronssuppliedbyoneatom)

Theformationofacovalentbondcanbedescribedingraphicformandrelatedto the potential energies of the atoms involved. Using the formation of thehydrogen molecule as an example, we can show how the potential energychangesasthetwoatomsapproachandformacovalentbond.Intheillustrationthatfollows,frames(1),(2),and(3)showtheeffectonpotentialenergyastheatoms move closer to each other. In frame (3), the atoms have reached theconditionoflowestpotentialenergy,buttheinertiaoftheatomspullsthemevencloser,asshowninframe(4).Therepulsionbetweenthemthenforcesthetwonucleiitoastableposition,asshowninframe(5).

MetallicBondsInmostmetals,oneormoreofthevalenceelectronsbecomedetachedfromtheatomandmigrateina“sea”offreeelectronsamongthepositivemetalions.Theattractive force strength varies with the nuclear positive charge of the metalatomsandthenumberofelectronsinthiselectronsea.Bothofthesefactorsarereflected in the amount of heat required to vaporize the metal. The strongattraction between these differently charged particles forms ametallic bond.Because of this firm bonding, metals usually have highmelting points, showgreatstrength,andaregoodconductorsofelectricity.

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Metallicbondsarelikepositiveionsina“sea”ofelectrons.

INTERMOLECULARFORCESOFATTRACTIONThe term intermolecular forces refers to attractions between molecules.Although it is proper to refer to all intermolecular forces as van derWaalsforces,namedafterJohannesvanderWaals(Netherlands), thisconceptshouldbeexpandedforclarity.

Dipole-DipoleAttractionOnetypeofvanderWaalsforcesisdipole-dipoleattraction. Itwasshowninthediscussionofpolarcovalentbondingthat theunsymmetricaldistributionofelectronicchargesleadstopositiveandnegativechargesinthemolecules,whicharereferredtoasdipoles. Inpolarmolecularsubstances, thedipoleslineupsothatthepositivepoleofonemoleculeattractsthenegativepoleofanother.Thisismuch like the lineup of small barmagnets.The force of attraction betweenpolarmolecules is calleddipole-dipole attraction. These attractive forces arelessthanthefullchargescarriedbyionsinioniccrystals.

LondonDispersionForcesAnother type of van der Waals forces is called London dispersion forces.Foundinbothpolarandnonpolarmolecules,itcanbeattributedtothefactthatamolecule/atom that usually is nonpolar sometimes becomes polar because theconstantmotionofitselectronsmaycauseunevenchargedistributionatanyoneinstant.Whenthisoccurs,themolecule/atomhasatemporarydipole.Thisdipolecan thencausea second,adjacentatom tobedistortedand tohave itsnucleusattracted to the negative end of the first atom. London dispersion forces areaboutone-tenththeforceofmostdipoleinteractionsandaretheweakestofalltheelectrical forces thatactbetweenatomsormolecules.These forceshelp toexplainwhynonpolarsubstancessuchasnoblegasesandthehalogenscondenseinto liquids and then freeze into solids when the temperature is lowered

sufficiently. In general, they also explain why liquids composed of discretemoleculeswithnopermanentdipoleattractionhave lowboilingpoints relativetotheirmolecularmasses.Itisalsotruethatcompoundsinthesolidstatethatarebound mainly by this type of attraction have rather soft crystals, are easilydeformed, and vaporize easily. Because of the low intermolecular forces, themeltingpointsarelowandevaporationtakesplacesoeasilythatitmayoccuratroom temperature. Examples of such solids are iodine crystals andmoth balls(paradichlorobenzeneandnaphthalene).

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Weakestofall,theLondondispersionforcesareone-tenththeforceofmostdipoleattractions.

HydrogenBondsAprotonorhydrogennucleushasahighconcentrationofpositivecharge.Whenahydrogenatomisbondedtoahighlyelectronegativeatom,itspositivechargewill have an attraction for neighboring electron pairs. This special kind ofdipole-dipoleattractioniscalledahydrogenbond.Themorestronglypolarthemoleculeis,themoreeffectivethehydrogenbondingisinbindingthemoleculesintoalargerunit.Asaresulttheboilingpointsofsuchmoleculesarehigherthanthose of similar nonpolar molecules. Good examples are water and hydrogenfluoride.StudyingFigure14showsthatintheseriesofcompoundsconsistingofH2O,

H2S,H2Se,andH2TeanunusualriseintheboilingpointofH2Ooccursthatisnotinkeepingwiththetypicalslowincreaseofboilingpointasmolecularmassincreases.InsteadoftheexpectedslopeofthelinebetweenH2OandH2S,whichisshowninFigure14asadashedline,theactualboilingpointofH2Oisquiteabithigher—100°C.TheexplanationisthathydrogenbondingoccursinH2Obutnottoanysignificantdegreeintheothercompounds.

Figure14.BoilingPointsofHydrogenCompoundswithSimilarElectronDotStructures

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Notice how hydrogen bondingelevates the boiling point of H2Oabovetheexpectedslope.

Thissamephenomenonoccurswiththehydrogenhalides(HF,HCl,HBr,andHI).Note inFigure14 thathydrogen fluoride,HF,whichhas stronghydrogenbonding,showsanunexpectedlyhighboilingpoint.Hydrogenbondingalsoexplainswhysomesubstanceshaveunexpectedlylow

vaporpressures,highheatsofvaporization,andhighmeltingpoints.Inorderforvaporizationormeltingtotakeplace,moleculesmustbeseparated.Energymustbeexpendedtobreakhydrogenbondsandthusbreakdownthelargerclustersofmoleculesintoseparatemolecules.Aswiththeboilingpoint, themeltingpointof H2O is abnormally high when compared with the melting points of thehydrogencompoundsoftheotherelementshavingsixvalenceelectrons,whicharechemicallysimilarbutwhichhavenoapparenthydrogenbonding.

DOUBLEANDTRIPLEBONDSTo achieve theoctet structure, which is an outer energy level resembling thenoble gas configuration of eight electrons, it is necessary for some atoms toshare two or even three pairs of electrons. Sharing two pairs of electronsproducesadoublebond.Anexample:

In the line formula,only the sharedpairof electrons is indicatedbyabond

(—).Thesharingofthreeelectronpairsresultsinatriplebond.Anexample:

Itcanbeassumedfromthesestructuresthatthereisagreaterelectrondensitybetween the nuclei involved and hence a greater attractive force between thenucleiandthesharedelectrons.Experimentaldataverify thatgreaterenergy isrequiredtobreakdoublebondsthansinglebonds,andtriplebondsthandoublebonds.Also, since these strongerbonds tend topull atomscloser together, theatomsjoinedbydoubleandtriplebondshavesmallerinteratomicdistancesandgreaterbondstrengths,respectively.

RESONANCESTRUCTURESIt isnotalwayspossible torepresent thebondingstructureofamoleculeby

eithertheLewisdotstructureorthelinedrawingbecausedataaboutthebondingdistance and bond strength are between possible drawing configurations andreally indicate a hybrid condition. To represent this situation, the possiblealternatives are drawnwith arrows between them.Classic examples are sulfurtrioxide and benzene. These structures are shown in Chapters 13 and 14,respectively,butarerepeatedhereasexamples.

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Resonance structure is a hybrid ofthepossibledrawingsbecausenooneLewis structure can represent thesituation.

Sulfurtrioxideresonancestructures:

Benzeneresonancestructures:

MOLECULARGEOMETRY—VSEPR—ANDHYBRIDIZATION

VSEPR—ElectrostaticRepulsionPropertiesofmoleculesdependnotonlyonthebondingofatomsbutalsoonthemolecular geometry—the three-dimensional arrangement of the molecule’satomsinspace.Thecombinationofthepolarityofthebondsandthegeometryof the molecule determine the molecular polarity. This can be defined as theunevendistributionofthemolecularcharge.Thechemicalformularevealslittleinformation about a molecule’s geometry. It is only after doing many testsdesignedtorevealtheshapesofthevariousmoleculesthatchemistsdevelopedtwodifferent yet equally successful theories to explain certain aspects of theirfindings.Onetheoryaccountsstructurallyformolecularbondangles.Theotherisusedtodescribechangesintheorbitalsthatcontainthevalenceelectronsofamolecule’satoms.ThestructuraltheorythatdealswiththebondanglesiscalledtheVSEPRtheory,whereas theone thatdescribeschanges in theorbitals thatcontain the valence electrons is called the hybridization theory. (VSEPRrepresentsValenceShellElectronPairRepulsion.)

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Two theories explain molecularstructure: VSEPR theory uses

valence shell electron pair repulsion.Hybridization theory uses changesin the orbitals of the valenceelectrons.

VSEPRuses as its basis the fact that like chargeswill orient themselves insuchawayastodiminishtherepulsionbetweenthem.

1.Mutualrepulsionoftwoelectroncloudsforcesthemtotheoppositesidesofasphere.Thisiscalledalineararrangement.

EXAMPLE:BeF2,beryliumfluoride

2.Minimumrepulsionbetweenthreeelectronpairsoccurswhenthepairsareattheverticesofanequilateraltriangleinscribedinasphere.Thisarrangementiscalledatrigonal-planararrangement.

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These basic arrangements areimportanttolearn!

EXAMPLE:BF3,borontrifluoride

3.Fourelectronpairsarefarthestapartattheverticesofatetrahedroninscribedinasphere.Thisarrangementiscalledatetrahedral-shapeddistributionofelectronpairs.

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Configurations often appear asquestionsontheSATtest.

EXAMPLE:CH4,methane

4.Mutualrepulsionofsixidenticalelectroncloudsdirectsthemtothecornersofaninscribedregularoctahedron.Thisissaidtohaveanoctahedralarrangement.

EXAMPLE:SF6,sulfurhexafluoride

VSEPRandUnsharedElectronPairsAmmonia,NH3,andwater,H2O,areexamplesofmoleculesinwhichthecentralatom has both shared and unshared electron pairs. Here is how the VSEPRtheoryaccountsforthegeometriesofthesemolecules.TheLewisstructureofammoniashowsthat,inadditiontothethreeelectron

pairsthecentralnitrogenatomshareswiththethreehydrogenatoms,italsohasoneunsharedpairofelectrons:

VSEPRtheorypostulatesthatthelonepairoccupiesspacearoundthenitrogenatomjustasthebondingpairsdo.Thus,asinthemethanemoleculeshownintheprecedingsection,theelectronpairsmaximizetheirseparationbyassumingthe

fourcornersofatetrahedron.Lonepairsdooccupyspace,butourdescriptionofthe observed shape of a molecule refers to the positions of atoms only.Consequently, as shown in the drawing below, the molecular geometry of anammonia molecule is that of a pyramid with a triangular base. The generalVSEPR formula for a molecule such as ammonia (NH3) is AB3E, where AreplacesN,BreplacesH,andErepresentstheunsharedelectronpair.Awatermoleculehas twounsharedelectronpairsandcanberepresentedas

anAB2E2molecule.Here,theoxygenatomisatthecenterofatetrahedron,withtwo corners occupied by hydrogen atoms and two by the unshared pairs, asshown below. Again, VSEPR theory states that the lone pairs occupy spacearoundthecentralatombutthattheactualshapeofthemoleculeisdeterminedonlybythepositionsoftheatoms.Inthecaseofwater,thisresultsina“bent,”orangular,molecule.

VSEPRandMolecularGeometryThefollowingtablesummarizesthemolecularshapesassociatedwithparticulartypesofmolecules.Notice that, inVSEPR theory,doubleand triplebondsaretreatedinthesamewayassinglebonds.ItishelpfultousetheLewisstructuresandthistabletogethertopredicttheshapesofmoleculeswithdoubleandtriplebonds,aswellastheshapesofpolyatomicions.

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Know these molecular and Lewisstructures.

HybridizationThemolecularconfigurationsderivedbyVSEPRcanalsobearrivedatthroughtheconceptofhybridization.Brieflystated, thismeans thatchemistsenvisionthattwoormorepureatomicorbitals(usuallys,p,andd)canbemixedtoformtwo ormore new hybrid atomic orbitals that are identical and conform to theknownshapesofmolecules.Hybridizationcanbeillustratedasfollows:

1.spHybridOrbitals

Spectroscopicmeasurementsofberylliumfluoride,BeF2,revealabondangleof180°andequalbondlengths.

Thegroundstateofberylliumis:

To accommodate the experimental data, we theorize that a 2s electron isexcited to a 2p orbital; then the two orbitals hybridize to yield two identicalorbitalscalledsporbitals.Eachcontainsoneelectronbut iscapableofholdingtwoelectrons.

2.sp2HybridOrbitalsBorontrifluoride,BF3,hasbondanglesof120°ofequalstrength.Toaccommodatethesedata,theboronatomhybridizesfromitsgroundstateof1s22s22p1to:

3.sp3HybridOrbitalsMethane,CH4,canbeusedtoillustratethishybridization.Carbonhasagroundstateof1s22s22p2.One2selectronisexcitedtoa2porbital,andthefourinvolvedorbitalsthenformfournewidenticalsp3orbitals.

Insomecompoundswhereonlycertainsp3orbitalsareinvolvedinbonding,distortion in the bond angle occurs because of unbonded electron repulsion.Examples:

a.Water,H2O

b.Ammonia,NH3

4.sp3d2HybridOrbitalsTheseorbitalsareformedfromthehybridizationofansandapelectronpromotedtodorbitalsandtransformedintosixequalsp3d2orbitals.Thespatialformisshownbelow.Sulfurhexafluoride,SF6,illustratesthishybridization.

Theconceptofhybridizationissummarizedintheaccompanyingtable.

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Know these hybrid orbitalsdesignationsandtheircorrespondingshapes.

SIGMAANDPIBONDSWhen bonding occurs between s and p orbitals, each bond is identified by aspecial term. A sigma bond is a bond between s orbitals, or an s orbital andanother orbital such as a p orbital. It includes bonding between hybrids of s

orbitalssuchassp,sp2,andsp3.Inthemethanemolecule,thesp3orbitalsareeachbondedtohydrogenatoms.

Thesearesigmabonds.

When two p orbitals share electrons in a covalent bond, the result is a pibond.Hereisanexample:

Chapter14givesmoreexamplesofsigmaandpibonding.

PROPERTIESOFIONICSUBSTANCESLaboratory experiments reveal that, in general, ionic substances arecharacterizedbythefollowingproperties:

1.Inthesolidphaseatroomtemperaturetheydonotconductappreciableelectriccurrent.

2.Intheliquidphasetheyarerelativelygoodconductorsofelectriccurrent.Theconductivityofionicsubstancesismuchsmallerthanthatofmetallicsubstances.

3.Theyhaverelativelyhighmeltingandboilingpoints.Thereisawidevariationinthepropertiesofdifferentioniccompounds.Forexample,potassiumiodide(KI)meltsat686°Candboilsat1,330°C,whilemagnesiumoxide(MgO)meltsat2,800°Candboilsat3,600°C.BothKIandMgOareioniccompounds.

4.Theyhaverelativelylowvolatilitiesandlowvaporpressures.Inotherwords,theydonotvaporizereadilyatroomtemperature.

5.Theyarebrittleandeasilybrokenwhenstressisexertedonthem.

6.Thosethataresolubleinwaterformelectrolyticsolutionsthataregoodconductorsofelectricity.Thereis,however,awiderangeinthesolubilitiesofioniccompounds.Forexample,at25°C,92gramsofsodiumnitrate(NaNO3)dissolvesin100gramsofwater,whileonly0.0002gramsofbariumsulfate(BaSO4)dissolvesinthesamemassofwater.

PROPERTIESOFMOLECULARCRYSTALSANDLIQUIDSExperiments have shown that these substances have the following generalproperties:

1.Neithertheliquidsnorthesolidsconductelectriccurrentappreciably.

2.Manyexistasgasesatroomtemperatureandatmosphericpressure,andmanysolidsandliquidsarerelativelyvolatile.

3.Themeltingpointsofsolidcrystalsarerelativelylow.

4.Theboilingpointsoftheliquidsarerelativelylow.

5.Thesolidsaregenerallysoftandhaveawaxyconsistency.

6.Alargeamountofenergyisoftenrequiredtodecomposethesubstancechemicallyintosimplersubstances.

ChapterSummary

Thefollowingtermssummarizealltheconceptsandideasthatwereintroducedinthischapter.Youshouldbeabletoexplaintheirmeaningandhowyouwouldusetheminchemistry.Theyappearinboldfacetypeinthischaptertodrawyourattentiontothem.Theboldfacetypealsomakesiteasierforyoutolookthemupif you need to. You could also use the search or “Google” action on yourcomputer to get a quick and expanded explanation of these terms, laws, andformulas.

covalentbond ionicbond stableoctetdipole-dipoleattraction Londondispersionforces sigmabondelectrostaticrepulsion metallicbond vanderWaalsforceshybridization pibond VSEPRhydrogenbond resonancestructure

InternetResourcesOnline content that reinforcesmajor concepts discussed in this chapter canbefound at the following Internet addresses if they are still available.Somemayhavebeenchangedordeleted.ChemicalBondingWorksheetwww.avon-chemistry.com/chem_bond_explain.htmlThissiteoffersafairlycompletelookattheconceptofchemicalbondingforthebeginningchemistrystudent.VSEPR(ValenceShellElectronPairRepulsion)Theorywinter.group.shef.ac.uk/vsepr/This site is a good tutorial on molecular shapes utilizing the Valence ShellElectronPairRepulsionTheory.

PracticeExercises

ThefollowingquestionsareintheformatthatisusedontheSATSubjectAreaTestinChemistry.Ifyouarenotfamiliarwiththesetypesofquestions,study

beforedoingthesereviewquestions.

Directions: The following set of lettered choices refers to the numberedquestions immediatelybelow it.For eachnumbered item,choose theoneletteredchoice that fits itbest.Then fill in thecorrespondingovalon theanswersheet.Eachchoiceinthesetmaybeusedonce,morethanonce,ornotatall.

Questions1–7

(A)ionic(B)covalent(C)polarcovalent(D)metallic(E)hydrogenbonding

1.Whentheelectronegativitydifferencebetweentwoatomsis2,whattypeofbondcanbepredicted?

2.Iftwoatomsarebondedinsuchawaythatbothmembersofthepairequallyshareoneelectronwiththeother,whatisthebondcalled?

3.Whichofthefivechoicesisconsideredtheweakestbondinthegroup?

4.Whichoftheabovebondsexplainswater’sabnormallyhighboilingpoint?

5.Ifthesharingofanelectronpairisunequalandtheatomshaveanelectronegativitydifferenceof1.4to1.6,whatisthistypeofsharingcalled?

6.Ifanelectronislostbyoneatomandcompletelycapturedbyanother,whatisthistypeofbondcalled?

7.Ifoneormorevalenceelectronsbecomedetachedfromtheatomsandmigrateina“sea”offreeelectronsamongthepositivemetalions,whatisthistypeofbondingcalled?

Directions:

Every question below contains two statements, I in the left-hand column

andIIintheright-handcolumn.Foreachquestion,decideifstatementIistrue or false and whether statement II is true or false, and fill in thecorrespondingTorFovals in theanswerspaces.*Fill inovalCEonly ifstatementIIisacorrectexplanationofstatementI.

I II8.Maximum

repulsionbetweentwoelectronpairsinamolecularcompoundwillresultinalinearstructure

BECAUSE

theVSEPRmodelsaysthatlikechargeswillorientthemselvessoastodiminishtherepulsionbetweenthem.

9.Sodiumchlorideisanexampleofionicbonding

BECAUSEsodiumandchlorinehavethesameelectronegativity.

10.Ammoniahasatrigonalpyramidalmolecularstructure

BECAUSE

ammoniahasatetrahedralelectronpairgeometrywiththreeatomsbondedtothecentralatom.

*FillinovalCEonlyifIIisacorrectexplanationofI.

AnswersandExplanations1.(A)Whentheelectronegativitydifferencebetweenthetwoatomsisgreaterthan1.7,thebondbetweenthemisconsideredmorethan50%ionic.

2.(B)Whentwoatomsequallyshareapairofelectrons,thebondisconsideredcovalent.Withanelectronegativitydifferenceof0to0.3,thebondisstillconsideredcovalent.

3.(E)Hydrogenbondingistheweakestbecauseitistheweakattractionofthehydrogenendofapolarmoleculetothepartialnegativechargeofanadjacentmolecule.Especiallystronginwater,itisresponsibleformanyofwater’sproperties.

4.(E)Becauseofthestronghydrogenbondinginwater,ittakesmuchmoreenergytocausethemoleculestobreakawayfromeachotherintheliquidstateandchangetosteam.

5.(C)Whentheelectronegativitydifferencebetweenthetwobondingatomsisbetween0.3and1.7,theelectronsarenotequallysharedandresultinapolarcovalentbond.

6.(A)Thisisthedefinitionofapureionicbond.

7.(D)Metallicbondsaredefinedasa“sea”offreeelectronsthatmigratethroughthemetal.

8.(T,T,CE)Themutualrepulsionoftwoelectroncloudsforcesthemtotheoppositesidesofasphere.AnexampleisBeF2,whichformsalinearmolecularstructurelikethis,F–Be–F.

9.(T,F)Thebondbetweensodiumandchlorineinsodiumchlorideisionic,becausethedifferencebetweentheirelectronegativityisgreaterthan1.7.

10.(T,T,CE)ThemolecularstructureofNH3isatrigonalpyramidalstructurelikethis.

CHAPTER4

ChemicalFormulas

TheseskillsareusuallytestedontheSATSubjectTestinChemistry.Youshouldbeableto...•Recallandusethebasicrulesaboutoxidationstatestowritecorrectformulas.Thisincludeswritingformulaswithpolyatomicions.

•Namecompounds(acids,bases,andsalts)usingtheStocksystemandtheprefixsystem,andwritetheirformulas.

•Calculatetheoxidationstatesofanelementinanyformula.•Calculatetheformulamassofacompoundandthepercentcompositionofeachelement.

•Calculatetheempiricalformulawhengiventhepercentcompositionofeachelement.Whengiventheformulamass,youshouldbeabletofindthetrueformula.

•Writeasimplebalancedequation,indicatingthephase(orstate)ofthereactantsandproducts.

This chapter will review and strengthen these skills. Be sure to do thePracticeExercisesattheendofthechapter.

NAMINGANDWRITINGCHEMICALFORMULASWith theknowledgeyouhave about atomic structure, the significanceof eachelement’splacementintheperiodictable,andthebondingofatomsinionicandcovalent arrangements, you can now use this information towrite appropriateformulas and name the resulting products. Obviously, many compounds canresult. Some system of writing the names and formulas of these manycombinationswasneeded.Thesystemexplainedinthistextisanorganizedwayofaccomplishingthis.Itusesthreecategories:

CATEGORYI—Binaryioniccompoundswherethemetalpresentformsonlya

singletypeofpositivelychargedion(cation)CATEGORYII—Binaryioniccompoundswherethemetalformsmorethanonetypeofioniccompoundwithagivennegativelychargedion(anion)

CATEGORYIII—Binarycovalentcompoundsformedbetweentwononmetals

Table 6 is a list of ions that are often encountered in a first-year chemistrycourse.Youshouldknowthem.Althoughusing theperiod tablecanhelpyouwrite the symbol and apparent charge of cations and anions, knowing thesecommonionscanhelpyouwriteformulasandequations.

CategoryI—BinaryIonicCompoundsCategoryIbinaryioniccompoundsaremetallicionsfromgroups1and2ofthePeriodic Table. Thesemetallic ions have only one type of charge. The binaryioniccompoundsformedarecomposedofapositiveion(cation)thatiswrittenfirstandanegativeion(anion).Thefollowingrulesshowhowtonameandwritetheformulasforbinaryioniccompounds.CaCl2isusedasanexample.

1.Namethecationfirstandthentheanion.

2.Themonoatomic(one-atom)cationtakesitsnamefromthenameoftheelement.Thereforethecalciumion,Ca2+,iscalledcalciumanditschemicalsymbolappearsfirst.

3.Themonoatomicanionwithwhichthecationcombinesisnamedbytakingtherootoftheelement’snameandadding–ide.Youmustknowthisrule.Theanion’snamecomessecond.Therefore,thechlorineion,Cl−,iscalledchloride.

4.Thenameofthiscompoundiscalciumchloride.

Aquickwaytodeterminetheformulaofabinaryioniccompoundistousethecrisscrossrule.

EXAMPLE1:Todeterminetheformulaforcalciumchloride,firstwritetheionicformswiththeirassociatedcharges.

Nextmovethenumericalvalueofthemetalion’ssuperscript(withoutthecharge)tothesubscriptofthenonmetal’ssymbol.Thentakethenumericalvalueofthenonmetal’ssuperscriptandmakeitthesubscriptofthemetalasshownabove.

Notethatthenumericalvalue1isnotshowninthefinalformula.

Younowhavethechlorine’s1asthesubscriptofthecalciumandthecalcium’s2asthesubscriptofthechloride.Asaresult,youhaveCaCl2asthefinalformulaforcalciumchloride.

EXAMPLE2:Writethenameandformulafortheproductformedwhenaluminumreactswithoxygen.Firstwritethename.

1.Namethecationfirstandthentheanion.

2.Themonoatomic(one-atom)cationtakesitsnamefromthenameoftheelement.Thereforethealuminumion,Al3+,iscalledaluminumanditschemicalsymbolappearsfirst.

3.Themonoatomicanionwithwhichthecationcombinesisnamedbytakingtherootoftheelement’snameandadding–ide.Youmustknowthisrule.Theanion’snamecomessecond.Thereforetheoxygenion,O2−,iscalledoxide.

4.Thenameofthiscompoundisaluminumoxide.

Todeterminetheformulaforaluminumoxide,firstwritetheionicformswiththeirassociatedcharges.

NextmovethenumericalvalueoftheAl’ssuperscript(withoutthecharge)tothesubscriptoftheOsymbol.Dothesamewiththe2oftheO.Inotherwords,crisscrossthevalues.Younowhavethe2asthesubscriptofthealuminumandthe3asasubscriptoftheoxygen.YounowhaveAl2O3asthefinalformulaforaluminumoxide.

Thiscrisscross rulegenerallyworksverywell. Inonesituation, though,youhave to be careful. Suppose you want to write the compound formed whenmagnesiumreactswithoxygen.Magnesium,analkalineearthmetalingroup2formsa2+cation,andoxygenformsa2−anion.YouwouldpredictitsformulabeMg2O2,butthisisincorrect.Afteryoudothecrisscrossing(unlessyouknowthat the compound actually exists, like H2O2), you need to reduce all thesubscriptsbyacommonfactor.Inthisexample,youcandivideallthesubscriptsby2togetthecorrectformulaformagnesiumoxide,MgO.Whenyouattempttowriteaformula,youshouldknowwhetherthesubstance

actually exists. For example, you could easily write the formula for carbonnitrate,butnochemisthaseverpreparedthiscompound.

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REMEMBERReduce all subscriptsby a common factor unless you aresurethecompoundexists,likeH2O2.

______*Ionicchargesareshownasnumericalexponentsfollowedbythecharge.

CategoryII—BinaryIonicCompoundsIncategoryIIbinaryioniccompounds,themetalsformmorethanoneion,eachwith a different charge. The metallic ions (cation) ionically bind with anegativelychargedion(anion).Thefollowingchartlistsmostofthemetalsthatformmorethanonetypeof

ionic cation and thereforemore than one binary ionic compoundwith a givenanion.

______*Thisformofmercury(I)ionsalwaysoccursbondedtogetherasaHg2

2+ion.

Althoughthefollowingmetalsare“transition”metals,theyformonlyonetypeofcation.SoaRomannumeralisnotusedwhennamingtheircompounds.

Ag1+SilverCd2+CadmiumZn2+Zinc

EXAMPLE:ThecompoundcontainingtheFe2+ionandthecompoundcontainingtheFe3+ionbothcombinewiththechlorideiontoformtwodifferentcompounds.Usingthecrisscrosssystem,yougettheformulaFeCl2foriron(II)chloride.

ThecompoundformedusingtheFe3+ionandthechlorideionisFeCl3,whichisiron(III)chloride.

Thenamesiron(II)chlorideandiron(III)chloridearearrivedatbyusingtheRomannumeralsinparenthesestoindicatethechargeofthemetallicionusedasthecation.

Another,oldersystemofnamingcategoryIIbinaryioniccompoundsisstillseeninsomebooks.Simplystated,formetals thatformonlytwoions, the ionwiththehigherchargehasanameendingin–icandtheionwiththelowerchargehasanameendingin–ous.In thissystem,Fe3+ iscalledtheferric ionandFe2+ iscalled the ferrous ion.Thenames forFeCl2andFeCl3are then ferric chlorideandferrouschloride,respectively.

ExamplesofCategoryIIBinaryIonicCompoundsFormula NameCuCl Copper(I)chlorideHgO* Mercury(II)oxideFeO* Ferrous(II)oxideMnO2

† Manganese(IV)oxidePbCl2 Lead(II)chloride

_____*Thesubscriptsarereducedandarenotwrittenbecausesubscriptsof1areunderstood.†Thesubscriptsarereduced.

The modified periodic chart that follows shows the location of the commoncategory I and category II ions. Also shown in this chart are the commonnonmetallicmonoatomicionsasanions.

CategoryIandIIIonicCompoundsFormedwithPolyatomicIonsAnothergroupofioniccompoundscontainspolyatomicions.Apolyatomicionisagroupofelementsthatactlikeasingleionwhenformingacompound.Thebondswithin these polyatomic ions are predominately covalent.However, thegroupasawholehasanexcesscharge,whichisusuallynegative,becauseofanexcessofelectrons.Ifthecompoundsformedwiththepolyatomicionsconsistofthreeelements,theyarecalledternarycompounds.

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You should memorize all thepolyatomic ions in Table 6 to helpyou use them in formulas andequations.

Polyatomic ions have special names and formulas that youmustmemorize.Table6 contains thenames and ionic chargesof the commonpolyatomic ionsencounteredinafirst-yearchemistrycourse.NotethatonlyonecommonlyusedpositivelychargedpolyatomicionisinTable6,theammoniumion,NH4

+.AlsonoticeinTable6thatseveralofthepolyatomicanionscontainanatom

of agivenelement andadifferentnumberofoxygenatoms, suchasNO2andNO3.When thereare twomembersof suchaseries, thenameof theonewithfewer oxygen atoms ends in -ite and the name of the one with more oxygenatomsendsin–ate.Thefollowingtableshowsexamplesofpolyatomicionsofsulfur.

Sometimes an element combines with oxygen to form more than just twopolyatomicions,suchasClO−,ClO2

−,ClO3−,andClO4

−.Whenthisoccurs,theprefixhypo-isusedtonamethepolyatomicionwiththefewestoxygenionsandtheprefixper-tonamethepolyatomicionwiththemostoxygenions.

WritingFormulaswithPolyatomicIonsWhen writing formulas using polyatomic anions, the rules do not change.Simplytreatthepolyatomicionasifitwereasingleanion.Ifthecationisfromcategory I, follow the rules for category I. If the cation is from category II,followtherulesforcategoryII.Thecrisscrossmethoddoesnotchange,either.

EXAMPLE1:Usethecrisscrossmethodtowritetheformulaforcalciumsulfate,acategoryIcationandapolyatomicion.

Calciumsulfate

ThefinalformulaisCaSO4.Noticethatthesubscripts“2”areomitted.

EXAMPLE2:Usethecrisscrossmethodtowritetheformulaforiron(III)sulfate,acategoryIIcationandapolyatomicion.

Iron(III)sulfate

ThefinalformulaisFe2(SO4)3.

CategoryIII—BinaryCovalentCompoundsBinarycovalentcompoundsareformedbetweentwononmetals.Althoughthesecompoundsdonot contain ions, they arenamedvery similarly tobinary ioniccompounds.Tonamebinarycovalentcompounds,usethesesteps.

1.Thefirstelementintheformulaisnamedfirst,usingthefullelementalname.

2.Thesecondelementisnamedasifitwereananionandusesitselementalname.

3.Prefixesareusedtodenotethenumberofthesecondelementpresent.Theseprefixesareshowninthetablebelow.

4.Theprefixmono-isneverusedfornamingthefirstelement.Forexample,COiscalledcarbonmonoxide,notmonocarbonmonoxide.

Thefollowingareexamplesofcovalentcompoundsformedfromthenonmetalsnitrogenandoxygen,usingtherulesabove.

Compound SystematicName CommonNameN2O Dinitrogenmonoxide* Nitrousoxide

NO Nitrogenmonoxide* NitricoxideNO2 NitrogendioxideN2O3 DinitrogentrioxideN2O4 Dinitrogentetroxide*

N2O5 Dinitrogenpentoxide*

* Notice that for ease of pronunciation, the final “a” or “o” of the prefix isdroppediftheelementbeginswithavowel.Towrite the formula for binary covalent compounds, use the same steps as

whenwritingtheformulaofioniccompounds.

1.Thesymbolofthefirstelementintheformulaiswrittenfirst,followedbythesecondelement.

2.Usetheprefix(es)denotedinthenameforthenumberofeachelementpresentintheformula.

Thefollowingshowsomeexamplesofbinarycovalentcompounds.

Name FormulaSulfurhexafluoride SF6Phosphorustrichloride PCl3

OXIDATIONSTATESANDFORMULAWRITINGTokeeptrackofthetransferofelectronsinallformulas,chemistshavedeviseda

system of electron bookkeeping called oxidation states (or oxidationnumbers). In thismethod, anoxidation state is assigned toeachmemberof aformulaorpolyatomicion.Itisdesignatedbyasmall,whole-numbersuperscriptpreceded by a plus or minus sign. This is not to be confused with the ionicchargeswehavebeenusing thus far thatareused to the rightof ioniccharge.Thesechargesaredirectlyrelatedtothebondingthatoccursincompoundsandwas discussed in the previous chapter. Oxidation states are also used to trackelectrontransfers.Thisisdiscussedinthechapteraboutoxidationandreduction.

TheRulesforAssigninganOxidationStateBeloware thebasic rules for assigninganoxidation state to eachelement.Byapplying simple rules, oxidation states can be assigned to most elements orcompounds.Toapplytheserules,rememberthatthesumoftheoxidationstatesmustbezeroforanelectricallyneutralcompound.Foranion,thesumoftheoxidationstatesmustequalthechargeontheion.

1.Theoxidationstateofanatominanelementiszero.Examples:0forNa(s),O2(g),andH(l)

2.Theoxidationstateofamonoatomicionisthesameasitscharge.Examples:Na+1,Cl−1

3.Theoxidationstateoffluorineis−1initscompounds.Examples:HFas1H(+1)+1F(−1)=0;PF3as1P(+3)+3F(−1)=0

4.Theoxidationstateofoxygenisusually−2initscompounds.Example:H2Owhere2H(+1)+1O(−2)=0(Exceptionsoccurwhentheoxygenisbondedtofluorineandtheoxidationstateoffluorinetakesprecedenceandinperoxidecompoundswheretheoxidationstateisassignedthevalueof−1.)

5.Theoxidationstateofhydrogeninmostcompoundsis+1.Examples:H2O,HCl,NH3(Inhydrides,thereisanexception.Oxygenisassignedthevalueof−1.)

SomeExamplesofUsingOxidationStatesinFormulas

EXAMPLE1:InNa2SO4,whatistheoxidationstateofsulfur?

Sincethepositivesumplusthenegativesummustequal0,

(+2)+x+(−8)=0

Thesulfurmusthavea+6oxidationstate.

EXAMPLE2:WhatistheoxidationstateofchromiuminK2Cr2O7?

K=2×(+1)=+2Cr=2×(x)=2xO=7×(−2)=−14

(+2)+(2x)+(−14)=02x=+12x=+6

Thechromiumhasa+6oxidationstate.

Inapolyatomicion,thealgebraicsumofthepositiveandnegativeoxidationstatesofalltheatomsintheformulamustbeequaltothechargeoftheion.

EXAMPLE3:WhatistheoxidationstateofsulfurinSO42−?

S=1×(x)=xO=4×(−2)=−8

Sincetheymustequal−2(thechargeoftheion),

x+(−8)=−2x=+6

Sulfurmusthavea+6oxidationstateintheion.

NAMESANDFORMULASOFCOMMONACIDSANDBASESThedefinitionofanacidandabase isexpanded later inafirst-yearchemistrycourse. For now, common acids are aqueous solutions containing excesshydrogen ions, H+. Common bases are aqueous solutions containing excesshydroxideions,OH−.Abinaryacidisnamedbyplacingtheprefixhydro-infrontofthestemorfull

name of the nonmetallic element, and adding the ending -ic. Examples arehydrochloricacid(HCl)andhydrosulfuricacid(H2S).A ternary compound consists of three elements, usually an element and a

polyatomic ion.Toname the compound,youmerelynameeachcomponent intheorderofpositivefirstandnegativesecond.Ternaryacidsusuallycontainhydrogen,anonmetal,andoxygen.Becausethe

amountofoxygenoftenvaries,thenameofthemostcommonformoftheacidintheseriesconsistsofmerelythestemofthenonmetalwiththeending-ic.Theacid containing one less atom of oxygen than the most common acid isdesignatedbytheending-ous.Thenameoftheacidcontainingonemoreatomofoxygen than themostcommonacidhas theprefixper-and theending-ic ;thatof theacidcontainingone lessatomofoxygen than the -ousacidhas theprefix hypo- and the ending -ous. This is evident in Table 7 with the acidscontainingH,Cl,andO.Youcanrememberthenamesofthecommonacidsandtheirsaltsbylearning

thefollowingsimplerules:

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Learntheserules.

When thenameof the ternary acidhas theprefixhypo- orper-, that prefix is

retainedinthenameofthesalt(hypochlorousacid=sodiumhypochlorite).ThenamesandformulasofsomecomonacidsandbasesarelistedinTable7.

CHEMICALFORMULAS:THEIRMEANINGANDUSEAs you have seen, a chemical formula is an indication of the makeup of acompoundintermsofthekindsofatomsandtheirrelativenumbers.Italsohassome quantitative applications. By using the atomic masses assigned to theelements,wecanfindtheformulamassofacompound.Ifwearesurethattheformularepresentstheactualmakeupofonemoleculeofthesubstance,thetermmolecularmassmaybeusedaswell.Insomecasestheformularepresentsan

ioniclatticeandnodiscretemoleculeexists,asinthecaseoftablesalt,NaCl,ortheformulamerelyrepresentsthesimplestratioofthecombinedsubstancesandnotamoleculeofthesubstance.Forexample,CH2isthesimplestratioofcarbonandhydrogenunitedtoformtheactualcompoundethylene,C2H4.Thissimplestratioformulaiscalledtheempiricalformula,andtheactualformulaisthetrueformula.Theformulamassisdeterminedbymultiplyingtheatomicmassunits(as a whole number) by the subscript for that element and then adding thesevaluesforalltheelementsintheformula.Forexample:Ca(OH)2(onecalciumamu+twohydrogenandtwooxygenamu=formula

mass).1Ca(amu=40)=402O(amu=16)=322H(amu=1)=2.0

FormulamassCa(OH)2=74amu(orµ)

InChapter 6, the concept of amole is introduced. If you have 6.02× 1023atomsofanelement,thentheatomicmassunitscanbeexpressedingrams,andthentheformulamasscanbecalledthemolarmass.AnotherexampleisFe2O3.

2Fe(amu=56)=1123O(amu=16)=48.0

FormulamassFe2O3=160.amu

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Knowhowtocomputethepercentagecomposition of an element in acompound.

Itissometimesusefultoknowwhatpercentofthetotalweightofacompoundis made up of a particular element. This is called finding the percentagecomposition.Thesimpleformulaforthisis:

To find the percent composition of calcium in calcium hydroxide in theexampleabove,wesettheformulaupasfollows:

Tofindthepercentcompositionofoxygenincalciumhydroxide:

Tofindthepercentcompositionofhydrogenincalciumhydroxide:

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This type of question alwaysappearsonthetest.

ANOTHEREXAMPLE:FindthepercentcompositionsofCuandH2OinthecompoundCuSO4·5H2O(thedotisread“with”).

First,wecalculatetheformulamass:1Cu=64amu1S=32amu4O=64(4×16)amu5H2O=90.(5×18)amu250amu

andthenfindthepercentages:

PercentageCu:

PercentageH2O:

Whenyouaregiventhepercentageofeachelementinacompound,youcanfindtheempiricalformulaasshownwiththefollowingexample:Given that a compound is composed of 60.0%Mg and 40.0%O, find the

empiricalformulaofthecompound.

1.Itiseasiesttothinkof100massunitsofthiscompound.Inthiscase,the100massunitsarecomposedof60.amuofMgand40.amuofO.Becauseyouknowthat1unitofMgis24amu(fromitsatomicmass)and,likewise,1unitofOis16,youcandivide60by24tofindthenumberofunitsofMginthecompoundanddivide40.by16tofindthenumberofunitsofOinthecompound.

2.Now,becauseweknowformulasaremadeupofwhole-numberunitsoftheelements,whichareexpressedassubscripts,wemustmanipulatethesenumberstogetwholenumbers.Thisisusuallyaccomplishedbydividingthesenumbersbythesmallestquotient.Inthiscasetheyareequal,sowedivideby2.5.

3.SotheempiricalformulaisMgO.

ANOTHEREXAMPLE:Given:Ba=58.81%,S=13.73%,andO=27.46%.Findtheempiricalformula.

1.Divideeachpercentbytheamuoftheelement.

2.Manipulatenumberstogetsmallwholenumbers.Trydividingthemallby

thesmallestfirst.Inthiscase,divideeachresultby0.43,asshownbelow.

3.TheformulaisBaSO4.

Insomecasesyoumaybegiventhetrueformulamassofthecompound.Tocheck if your empirical formula is correct, add up the formula mass of theempirical formulaandcompare itwith thegiven formulamass. If it isnot thesame,multiplytheempiricalformulabythesmallwholenumberthatgivesyouthecorrectformulamass.Forexample,ifyourempiricalformulaisCH2(whichhasaformulamassof14)andthetrueformulamassisgivenas28,youcanseethatyoumustdoubletheempiricalformulabydoublingall thesubscripts.ThetrueformulaisC2H4.

LAWSOFDEFINITECOMPOSITIONANDMULTIPLEPROPORTIONSIn the problems involving percent composition, we have depended on twothings: eachunit of an elementhas the sameatomicmass, and every time theparticularcompoundforms,itformsinthesamepercentcomposition.Thatthislatter statement is true no matter the source of the compound is theLaw ofDefiniteComposition. There are some compounds formed by the same twoelementsinwhichthemassofoneelementisconstant,butthemassoftheothervaries. In every case, however, the mass of the other element is present in asmall-whole-number ratio to theweightof the first element.This is called theLawofMultipleProportions.AnexampleisH2OandH2O2.

InH2OtheproportionofH:O=2:16or1:8InH2O2theproportionofH:O=2:32or1:16

Theratioofthemassofoxygenineachis8:16or1:2(asmall-whole-numberratio).

WRITINGANDBALANCINGSIMPLE

EQUATIONSAn equation is a simplified way of recording a chemical change. Instead ofwords,chemicalsymbolsandformulasareusedtorepresent thereactantsandtheproducts.Hereisanexampleofhowthiscanbedone.Thefollowingisthewordequationofthereactionofburninghydrogenwithoxygen:

Hydrogen+oxygenyieldswater.Replacingthewordswiththechemicalformulas,wehave

H2+O2→H2O

Wereplacedhydrogenandoxygenwiththeformulasfortheirdiatomicmolecularstatesandwrotetheappropriateformulaforwaterbasedontherespectiveoxidation(valence)numbersforhydrogenandoxygen.Notethatthewordyieldswasreplacedwiththearrow.Although the chemical statement tells what happened, it is not an equation

becausethetwosidesarenotequal.Whiletheleftsidehastwoatomsofoxygen,the right side has only one.Knowing that the Law ofConservation ofMatterdictates that matter cannot easily be created or destroyed, we must get thenumber of atoms of each element represented on the left side to equal thenumberontheright.Todothis,wecanonlyusenumbers,calledcoefficients,infront of the formulas. It is important to note that in attempting to balanceequations THE SUBSCRIPTS IN THE FORMULAS MAY NOT BECHANGED.

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You cannot change subscripts offormulas to attempt to balance anequation!

Lookingagainattheskeletonequation,wenoticethatif2isplacedinfrontofH2Othenumbersofoxygenatomsrepresentedonthetwosidesoftheequationare equal.However, there are now four hydrogens on the right sidewith onlytwoontheleft.Thiscanbecorrectedbyusingacoefficientof2infrontofH2.Nowwehaveabalancedequation:

2H2+O2→2H2O

Thisequationtellsusmorethanmerelythathydrogenreactswithoxygentoformwater. It has quantitativemeaning aswell. It tells us that twomolecularmasses of hydrogen react with one molecular mass of oxygen to form twomolecularmassesofwater.Becausemolecularmasses are indirectly related tograms,wemayalsorelatethemassesofreactantsandproductsingrams.

Thisaspectwillbeimportantinsolvingproblemsrelatedtothemassesofsubstancesinachemicalequation.Here isanother,moredifficultexample:Write thebalancedequation for the

burningofbutane(C4H10)inoxygen.First,wewritetheskeletonequation:

C4H10+O2yieldsCO2+H2O

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First deal with multiatomicreactants.

Lookingattheoxygens,weseethatthereareanevennumberontheleftbutanoddnumberontheright.Thisisagoodplacetostart.Ifweuseacoefficientof2forH2O,thatwillevenouttheoxygensbutintroducefourhydrogensontheright while there are ten on the left. A coefficient of 5 will give us the rightnumberofhydrogensbut introducesanoddnumberofoxygens.Thereforewehavetogotothenextevenmultipleof5,whichis10.Tengivesus20hydrogenatomsontheright.Byplacinganothercoefficientof2infrontofC4H10,wealsohave20hydrogenatomsontheleft.Nowthecarbonsneedtobebalanced.Byplacingan8infrontofCO2,wehaveeightcarbonsonbothsides.Theremainingstep is to balance the oxygens. We have 26 on the right side, so we need acoefficient of 13 in front of theO2on the left to give us 26 oxygens on both

sides.Ourbalancedequationis:

2C2H4+13O2→8CO2+10H2O

Formorepracticeinbalancingequations,seeChapter12.

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Besureyouhaveincludedallsourcesof a particular element since it mayoccurintwoormorecompounds.

SHOWINGPHASESINCHEMICALEQUATIONSOnceanequationisbalanced,youmaychoosetogiveadditionalinformationinthe equation. This can be done by indicating the phases of substances, tellingwhethereachsubstanceis in the liquidphase( ), thegaseousphase(g),or thesolidphase(s).Sincemanysolidswillnotreacttoanyappreciableextentunlessthey are dissolved in water, the notation (aq) is used to indicate that thesubstanceexistsinawater(aqueous)solution.Informationconcerningphaseisgiven in parentheses following the formula for each substance. Severalillustrationsofthisnotationaregivenbelow:

Anexampleofphasenotationinanequation:

2HCl(aq)+Zn(s)→ZnCl2(aq)+H2(g)In words, this says that a water solution of hydrogen chloride (called

hydrochloric acid) reactswith solid zinc to produce zinc chloride dissolved in

waterplushydrogengas.

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(g)=gaseousstate( )=liquidstate(s)=solidstate

WRITINGIONICEQUATIONSAttimes,chemistschoosetoshowonlythesubstancesthatreactinthechemicalaction. These equations are called ionic equations because they stress thereactionandproductionofions.Ifwelookattheprecedingequation,weseethecompletecastof“actors”:

Reactants2HCl(aq)releases→2H+(aq)+2Cl−(aq)insolutionZn(s)stayas→Zn(s)particlesProductsZnCl2(aq)releases→Zn2+(aq)+2Cl−(aq)insolutionH2(g)stayas→H2(g)molecules

Writingthecompletereactionusingtheseresults,wehave:

2H+(aq)+2Cl−(aq)+Zn(s)→Zn2+(aq)+2Cl−(aq)+H2(g)

Noticethatnothinghappenedtothechlorideion.Itappearsthesameonbothsidesoftheequation.Itisreferredtoasaspectatorion.Inwritingthenetionicequation,spectatorionsareomitted,sothenetionicequationis:

2H+(aq)+Zn(s)→Zn2−(aq)+H2(g)

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Innet ionic equations,donot show“spectator”ionsthatdonotchange.

ChapterSummaryThefollowingtermssummarizealltheconceptsandideasthatwereintroducedinthischapter.Youshouldbeabletoexplaintheirmeaningandhowyouwouldusetheminchemistry.Theyappearinboldfacetypeinthischaptertodrawyourattentiontothem.Theboldfacetypealsomakesiteasierforyoutolookthemupif you need to. You could also use the search or “Google” action on yourcomputer to get a quick and expanded explanation of these terms, laws, andformulas.

binarycompound netionicequation reactantscoefficient percentagecomposition stocksystemempiricalformula polyatomicion ternarycompoundformulamass products trueformulamolecularmass

LawofDefiniteCompositionLawofMultipleProportions

InternetResourcesOnline content that reinforcesmajor concepts discussed in this chapter canbefound at the following Internet addresses if they are still available.Somemayhavebeenchangedordeleted.InteractivePracticeonNamingIonicCompoundswww.teacherbridge.org/public/bhs/teachers/Dana/ionic.htmThissiteoffersaninteractivepracticeonnamingioniccompounds.ChemicalFormulaWritinghttp://www.fordhamprep.org/gcurran/sho/less0ns/lesson5.3.htmThissiteoffersaninteractivequizonwritingchemicalformulas.NamingChemicalCompoundshttp://www.fernbank.edu/Chemistry/nomen.htmlThissiteoffersaShockwaveFlashexerciseonchemicalnomenclature.BalancingChemicalReactionEquations

http://www.wfu.edu/~ylwong/balanceeq/balanceq.htmlThis site offers a tutorial on balancing simple reaction equationswith helpfulstep-by-stephints.

PracticeExercisesWritetheformulaornameinquestions1through10:

1.AgCl_____________________________

2.CaSO4____________________________

3.Al2(SO4)3__________________________

4.NH4NO3_________________________

5.FeSO4____________________________

6.Potassiumchromate__________________

7.Sodiumfluoride____________________

8.Magnesiumsulfite___________________

9.Copper(II)sulfate___________________

10.Iron(III)chloride___________________

Directions: The following set of lettered choices refers to the numberedquestions immediatelybelow it.For eachnumbered item,choose theoneletteredchoice that fits itbest.Then fill in thecorrespondingovalon theanswersheet.Eachchoiceinthesetmaybeusedonce,morethanonce,ornotatall.

Questions11-15

Use the following choices to indicate the oxidation state of the underlinedsymbolinthegivenformulas.

(A)+1

(B)+2(C)+4(D)+5(E)+6

11.K2CrO4

12.Na2S2O3

13.PO43-

14.CaCO3

15.Mg(HCO3)2

_________________________________________________

16.FindthepercentageofsulfurinH2SO4.

17.Whataretheempiricalformulaandthetrueformulaofacompoundcomposedof85.7%Cand14.3%Hwithatrueformulamassof42?

Directions:Every question below contains two statements, I in the left-hand columnandIIintherighthandcolumn.Foreachquestion,decideifstatementIistrue or false and whether statement II is true or false, and fill in thecorrespondingTorFovals in theanswerspaces.*Fill inovalCEonly ifstatementIIisacorrectexplanationofstatementI.

I II18.Intheformulaof

acompound,thealgebraicsumoftheoxidationnumbersmustbe0

BECAUSE oxygen’soxidationnumberinmostcompoundsis−2.

19.Fluorineis

assignedanoxidationnumberof−1inallcompounds

BECAUSEfluorineisthemostelectronegativeelement.

20.Balancedequationshavethesamenumberofreactantatomsastheproductatoms

BECAUSEtheconservationofmattermustapplyinallregularchemicalequations.

*FillinovalCEonlyifIIisacorrectexplanationofI.

21.Writethecompleteionicequationforthisreaction.Thenwritethenetionicequation.

3NaOH(aq)+Fe(NO3)3(aq)→3NaNO3(aq)+Fe(OH)3(s)

Completeionicequation:

_________________________→___________________________

Netionicequation:

_________________________→___________________________

AnswersandExplanations1.Silverchloride

2.Calciumsulfate

3.Aluminumsulfate

4.Ammoniumnitrate

5.Iron(II)sulfateorferroussulfate

6.K2CrO4

7.NaF

8.MgSO3

9.CuSO4

10.FeCl3

K+1CrxO−2

11.+6because2(+1)+1(x)+4(−2)=0,x=+6

Na+1SxO−2

12.+2because2(+1)+2(x)+3(-2)=0,x=+2

PxO−2

13.+5because1(x)+4(−2)=−3,x=+5

CaxC+4O−2

14.(B)+2,because1(x)+1(+4)+3(−2)=0,x=+2

Mg+2HxC+4O−2

15.(A)+1,because1(+2)+2(x)+2(+4)+6(−2)=0,x=1

16.H2SO4iscomposedof:

17.(C)=12)85.7%CH=1)14.3%H7.1414.3

Tofindthelowestratioofthewholenumbers:

7.14)7.147.14)14.31.02.0

TheempiricalformulaisCH2.Since theformulamass isgivenas42, theempirical formulaCH2,whichrepresents a mass of 14, divides into 42 three times. Therefore, the trueformulaisC3H6.

18.(T,T)Thesumofalltheoxidationtotalsforacompoundmustequal0,andoxygeninmostcompoundsisassigneda−2oxidationnumber,butthisdoesnotexplaintheIstatement.

19.(T,T,CE)StatementIIdoesexplainstatementI.

20.(T,T,CE)TheLawofConservationofMatterdoesrequirethatthereareequalnumbersofrespectiveatomsonbothsidesofaregular(notatomic)equation.Becausetheformulaofeachsubstanceisdeterminedbyoxidationnumbers,theequationisbalancedbyusingcoefficients.

21.Fromthisformulaequation:

3NaOH(aq)+Fe(NO3)3(aq)→3NaNO3(aq)+Fe(OH)3(s)Thecompleteionicequationis:

3Na+(aq)+3OH−(aq)+Fe3+(aq)+3NO3−(aq)→3Na+(aq)+

3NO3−(aq)+Fe(OH)3(s)

Thenetionicequationis:

Fe3+(aq)+3OH−(aq)→Fe(OH)3(s)

CHAPTER5

GasesandtheGasLaws

TheseskillsareusuallytestedontheSATSubjectTestinChemistry.Youshouldbeableto…•Describethephysicalandchemicalpropertiesofoxygenandhydrogenandtheelectronicmakeupoftheirdiatomicmolecules.

•Explainhowatmosphericpressureismeasured,howtoreadthepressureinamanometer,andtheunitsusedtomeasurepressure.

•Readandexplainagraphicdistributionofthenumberofmoleculesversuskineticenergyatdifferenttemperatures.

•Knowandusethefollowinglawstosolvegasproblems:Graham’s,Charles’s,Boyle’s,Dalton’s,theCombinedGasLaw,andtheIdealGasLaw.

This chapter will review and strengthen these skills. Be sure to do thePracticeExercisesattheendofthechapter.

When we discuss gases today, the most pressing concern is the gases in ouratmosphere.ThesearethegasesthatareheldagainstEarthbythegravitationalfield.Theprincipal constituents of the atmosphereofEarth today arenitrogen(78%) and oxygen (21%). The gases in the remaining 1% are argon (0.9%),carbondioxide(0.03%),varyingamountsofwatervapor,andtraceamountsofhydrogen,ozone,methane,carbonmonoxide,helium,neon,krypton,andxenon.Oxides and other pollutants added to the atmosphere by factories andautomobileshavebecomeamajorconcernbecauseoftheirdamagingeffectsinthe form of acid rain. In addition, a strong possibility exists that the steadyincrease in atmospheric carbon dioxide, mainly attributed to fossil fuelcombustion over the past century, may affect Earth’s climate by causing agreenhouseeffect,resultinginasteadyriseintemperaturesworldwide.

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The major components of Earth’s

atmosphere: 78% nitrogen, 21%oxygen

Studies of air samples show that up to 55 miles above sea level thecomposition of the atmosphere is substantially the same as at ground level;continuous stirringproducedby atmospheric currents counteracts the tendencyof the heavier gases to settle below the lighter ones. In the lower atmosphere,ozone is normally present in extremely low concentrations. The atmosphericlayer12 to30milesupcontainsmoreozone that isproducedby theactionofultraviolet radiation from the Sun. In this layer, however, the percentage ofozoneisonly0.001byvolume.Humanactivityaddstotheozoneconcentrationintheloweratmospherewhereitcanbeaharmfulpollutant.Theozonelayerbecameasubjectofconcernintheearly1970swhenitwas

found that chemicals known as fluorocarbons, or chlorofluoromethanes, wererisingintotheatmosphereinlargequantitiesbecauseoftheiruseasrefrigerantsandaspropellantsinaerosoldispensers.Theconcerncenteredonthepossibilitythat these compounds, through the action of sunlight, could chemically attackanddestroystratosphericozone,whichprotectsEarth’s surface fromexcessiveultraviolet radiation. As a result, U.S. industries and the EnvironmentalProtection Agency phased out the use of certain chlorocarbons andfluorocarbons as of the year 2000. There is still ongoing concern about boththeseenvironmentalproblems:thegreenhouseeffectandthedeteriorationoftheozonelayerasitrelatestopossibleglobalwarming.

SOMEREPRESENTATIVEGASESOxygenOf the gases that occur in the atmosphere, the most important one to us isoxygen.Although itmakesuponly approximately21%of the atmosphere, byvolume,theoxygenfoundonEarthisequalinweighttoalltheotherelementscombined.About50%ofEarth’scrust(includingthewatersonEarth,andtheairsurroundingit)isoxygen.(NoteFigure15.)

Figure15.CompositionofEarth’sCrust

The composition of air varies slightly from place to place because air is amixture of gases. The composition by volume is approximately as follows:nitrogen,78%;oxygen,21%;argon,1%.Therearealsosmallamountsofcarbondioxide,watervapor,andtracegases.

PREPARATIONOFOXYGEN. In 1774, an English scientist named JosephPriestleydiscoveredoxygenbyheatingmercuricoxideinanenclosedcontainerwith a magnifying glass. That mercuric oxide decomposes into oxygen andmercury can be expressed in an equation: 2HgO → 2Hg + O2. After hisdiscovery, Priestley visited one of the greatest of all scientists, AntoineLavoisier, in Paris. As early as 1773 Lavoisier had carried on experimentsconcerning burning, and they had caused him to doubt the phlogiston theory(that a substance calledphlogistonwas releasedwhen a substanceburned; thetheorywentthroughseveralmodificationsbeforeitwasfinallyabandoned).By1775, Lavoisier had demonstrated the true nature of burning and called theresultinggas“oxygen.”

Todayoxygenisusuallypreparedinthelabbyheatinganeasilydecomposedoxygen compound such as potassium chlorate (KClO3). The equation for thisreactionis:

2KClO3+MnO2→2KCl+3O2(g)+MnO2

ApossiblelaboratorysetupisshowninFigure16.

Figure16.APossibleLaboratoryPreparationofOxygen

Inthispreparationmanganesedioxide(MnO2)isoftenused.Thiscompoundisnotusedupinthereactionandcanbeshowntohavethesamecompositionasit hadbefore the reactionoccurred.Theonly effect it has is that it lowers thetemperatureneeded todecompose theKClO3, and thusspeedsup the reaction.Substances that behave in this manner are referred to as catalysts. Themechanismbywhich a catalyst acts is not completelyunderstood in all cases,but it is known that in some reactions the catalyst does change its structuretemporarily.ItseffectisshowngraphicallyinthereactiongraphsinFigure17.

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A catalyst speeds up the rate ofreaction by lowering the activationenergy needed for the reaction. Acatalystisnotconsumed.

Figure17.EffectofCatalystonReaction

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Graphic representation of how acatalyst lowers the requiredactivationenergy

PROPERTIESOFOXYGEN.Oxygen is a gas under ordinary conditions oftemperatureandpressure,anditisagasthatiscolorless,odorless,tasteless,andslightly heavier than air; all these physical properties are characteristic of thiselement. Oxygen is only slightly soluble in water, thus making it possible tocollectthegasoverwater,asshowninFigure16.Althoughoxygenwillsupportcombustion,itwillnotburn.Thisisoneofits

chemicalproperties.Theusualtestforoxygenistoloweraglowingsplintintothegasandseeiftheoxidationincreasesinitsratetoreignitethesplint.(Note:Thisisnottheonlygasthatdoesthis.N2Oreactsthesame.)

OZONE.Ozone is another form of oxygen and contains three atoms in itsmolecular structure (O3). Since ordinary oxygen and ozone differ in energycontent and form, they have slightly different properties. They are calledallotropicformsofoxygen.OzoneoccursinsmallquantitiesintheupperlayersofEarth’satmosphere,andcanbeformedintheloweratmosphere,wherehigh-voltage electricity in lightningpasses through the air.This formationof ozonealsooccursaroundmachineryusinghighvoltage.Thereactioncanbeshownbythisequation:

3O2+elec.→2O3

Becauseofitshigherenergycontent,ozoneismorereactivechemicallythanoxygen.Theozonelayerpreventsharmfulwavelengthsofultraviolet(UV)lightfrom

passing through Earth’s atmosphere. UV rays have been linked to biologicalconsequencessuchasskincancer.

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The ozone layer protects us fromUVraysfromthesun.

HydrogenPREPARATION OF HYDROGEN. Although there is evidence of thepreparationofhydrogenbefore1766,HenryCavandishwas the firstperson torecognizethisgasasaseparatesubstance.Heobservedthat,wheneveritburned,itproducedwater.Lavoisiernamedithydrogen,whichmeans“waterformer.”Electrolysis of water, which is the process of passing an electric current

throughwater tocause it todecompose, isonemethodofobtaininghydrogen.Thisisawidelyusedcommercialmethod,aswellasalaboratorymethod.Another method of producing hydrogen is to displace it from the water

moleculebyusing ametal.To choose themetal youmustbe familiarwith itsactivity with respect to hydrogen. The activities of the common metals areshowninTable8.

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Knowtherelativeactivityofmetals.

AsnotedinTable8,anyofthefirstthreemetalswillreactwithcoldwater;thereactionisasfollows:

Veryactivemetal+Water=Hydrogen+Metalhydroxide

Usingsodiumasanexample:

2Na+2HOH→H2(g)+2NaOH

With the metals that react more slowly, a dilute acid reaction is needed toproduce hydrogen in sufficient quantities to collect in the laboratory. Thisgeneralequationis:

Activemetal+Diluteacid→Hydrogen+Saltoftheacid

Anexample:

Zn+dil.H2SO4→H2(g)+ZnSO4

This equation shows the usual laboratory method of preparing hydrogen.Mossy zinc is used in a setup as shown in Figure 18. The acid is introduceddownthethistletubeafterthezincisplacedinthereactingbottle.Inthissortofsetup, youwould not begin collecting the gas that bubbles out of the deliverytubeforafewminutessothattheairinthesystemhasachancetobeexpelledandyoucancollectaratherpurevolumeofthegasgenerated.

Figure18.PreparationofanInsolubleGasbytheAdditionofLiquidtoOtherReactant

Inindustry,hydrogenisproducedby(1)theelectrolysisofwater,(2)passingsteamoverred-hotironorthroughhotcoke,or(3)bydecomposingnaturalgas(mostlymethane,CH4)withheat(CH4+H2O→CO+3H2).

PROPERTIES OF HYDROGEN. Hydrogen has the following importantphysicalproperties:

1.Itisordinarilyagas;colorless,odorless,tastelesswhenpure.

2.Itweighs0.9gramperliterat0°Cand1atmospherepressure.Thisis asdenseasair.

3.Itisslightlysolubleinwater.

4.Itbecomesaliquidatatemperatureof−240°Candapressureof13atmospheres.

5.Itdiffuses(movesfromplacetoplaceingases)morerapidlythananyothergas.ThispropertycanbedemonstratedasshowninFigure19.

Figure19.DiffusionofHydrogen

Here theH2 in thebeaker that is placedover theporous cupdiffuses fasterthrough the cup than the air candiffuse out.Consequently, there is a pressurebuildup in the cup, which pushes the gas out through the water in the lowerbeaker.

Thechemicalpropertiesofhydrogenare:

1.Itburnsinairorinoxygen,givingofflargeamountsofheat.Itshighheatofcombustionmakesitagoodfuel.

2.Itdoesnotsupportordinarycombustion.

3.Itisagoodreducingagentinthatitwithdrawsoxygenfrommanyhotmetal

oxides.

GENERALCHARACTERISTICSOFGASESMeasuringthePressureofaGasPressure is defined as force per unit area. With respect to the atmosphere,pressureistheresultoftheweightofamixtureofgases.Thispressure,whichiscalled atmospheric pressure, air pressure, or barometric pressure , isapproximately equal to the weight of a kilogram mass on every squarecentimeterofsurfaceexposedtoit.Thisweightisabout10newtons.Thepressureof the atmospherevarieswith altitude.Athigher altitudes, the

weightoftheoverlyingatmosphereisless,sothepressureisless.Airpressurealsovaries somewhatwithweather conditions as low- andhigh-pressure areasmovewithweatherfronts.Ontheaverage,however,theairpressureatsealevelcan support a columnofmercury760millimeters inheight.This average sea-level air pressure is known as normal atmospheric pressure, also calledstandardpressure.The instrument most commonly used for measuring air pressure is the

mercurybarometer.Thediagrambelowshowshow it operates.Atmosphericpressureisexertedonthemercuryinthedish,andthisinturnholdsthecolumnofmercuryup in the tube.This columnat standardpressurewillmeasure760millimetersabovethelevelofthemercuryinthedishbelow.

MercuryBarometer

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Read the top of the meniscus formercury but the bottom of themeniscusforwater.

Ingas-lawproblemspressuremaybeexpressedinvariousunits.Onestandardatmosphere(1atm)isequalto760millimetersofmercury(760mmHg)or760torr, a unit named for Evangelista Torricelli. In the SI system, the unit ofpressure is thepascal (Pa),named inhonorof the scientistof the samename,and standard pressure is 101,325 pascals or 101.325 kilopascals (kPa). Onepascal (Pa) isdefinedas thepressureexertedby the forceofonenewton(1N)actingonanareaofonesquaremeter.Inmanycases,asinatmosphericpressure,itismoreconvenienttoexpresspressureinkilopascals(kPa).

Adevicesimilartothebarometercanbeusedtomeasurethepressureofagasin a confined container. This apparatus, called amanometer , is illustratedbelow. A manometer is basically a U-tube containing mercury or some otherliquid.Whenbothendsareopentotheair,asin(1)inthediagram,theleveloftheliquidwillbethesameonbothsidessincethesamepressureisbeingexertedonbothendsofthetube.In(2)and(3),avesselisconnectedtooneendoftheU-tube.Nowtheheightofthemercurycolumnservesasameansofreadingthepressure inside the vessel if the atmospheric pressure is known. When thepressure inside thevessel is the same as the atmospheric pressureoutside, thelevelsof liquidare thesame.When thepressure inside isgreater thanoutside,thecolumnofliquidwillbehigheronthesidethatisexposedtotheair,asin(2).Conversely, when the pressure inside the vessel is less than the outsideatmospheric pressure, the additional pressure will force the liquid to a higherlevelonthesidenearthevessel,asin(3).

Manometer

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Knowhowtocalculatethepressurein a closed vessel like in themanometershown.

Kinetic-MolecularTheoryBy indirect observations, theKinetic-Molecular Theory has been arrived at toexplain the forces between molecules and the energy the molecules possess.TherearethreebasicassumptionstotheKinetic-MolecularTheory:

1.Matterinallitsforms(solid,liquid,andgas)iscomposedofextremelysmallparticles.Inmanycasesthesearecalledmolecules.Thespaceoccupiedbythegasparticlesthemselvesisignoredincomparisonwiththevolumeofthespaceinwhichtheyarecontained.

2.Theparticlesofmatterareinconstantmotion.Insolids,thismotionisrestrictedtoasmallspace.Inliquids,theparticleshaveamorerandompatternbutstillarerestrictedtoakindofrollingoveroneanother.Inagas,theparticlesareincontinuous,random,straight-linemotion.

3.Whentheseparticlescollidewitheachotherorwiththewallsofthecontainer,thereisnolossofenergy.

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Know these basic assumptions oftheKinetic-MolecularTheory.

SomeParticularPropertiesofGasesAsthetemperatureofagasisincreased,itskineticenergyisincreased,therebyincreasing the randommotion.At a particular temperaturenot all theparticleshave the samekinetic energy, but the temperature is ameasureof the averagekineticenergyoftheparticles.Agraphofthevariouskineticenergiesresemblesanormalbell-shapedcurvewiththeaveragefoundatthepeakofthecurve(seeFigure20).

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Whenyoureadthetemperatureofasubstance, you are measuring itsaveragekineticenergy.

Figure20.MolecularSpeedDistributioninaGasatDifferentTemperatures

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Diffusionmeansspreadingout.

Whenthetemperatureislowered,thegasreachesapointatwhichthekineticenergy can no longer overcome the attractive forces between the particles (ormolecules) and the gas condenses to a liquid. The temperature at which thiscondensationoccurs is related to the typeof substance thegas iscomposedofandthetypeofbondinginthemoleculesthemselves.Thisrelationshipofbondtype to condensation point (or boiling point) is pointed out in Chapter 3,“Bonding.”The random motion of gases in moving from one position to another is

referredtoasdiffusion.Youknowthat,ifabottleofperfumeisopenedinonecornerofaroom,theperfume,thatis,itsmolecules,willmoveordiffusetoallpartsoftheroomintime.Therateofdiffusionistherateofthemixingofgases.Effusion is the term used to describe the passage of a gas through a tiny

orifice into an evacuated chamber. The rate of effusionmeasures the speed atwhichthegasistransferredintothechamber.

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Effusion means passing of a gasthrough an orifice (like through theneckofaballoon).

GASLAWSANDRELATEDPROBLEMSGraham’sLawofEffusion(Diffusion)This law relates the rate at which a gas diffuses (or effuses) to the type ofmoleculeinthegas.Itcanbeexpressedasfollows:

The Rate of Effusion of a Gas IsInversely Proportional to the SquareRootofitsMolecularMass.

Hydrogen, with the lowest molecular mass, can diffuse more rapidly than

othergasesundersimilarconditions.

TYPEPROBLEM:

Comparetherateofdiffusionofhydrogentothatofoxygenundersimilarconditions.

Theformulais

LetAbeH2andBbeO2.

Thereforehydrogendiffusesfourtimesasfastasoxygen.

Indealingwiththegaslaws,astudentmustknowwhatismeantbystandardconditions of temperature and pressure (abbreviated as STP). The standardpressureisdefinedastheheightofmercurythatcanbeheldinanevacuatedtubeby 1 atmosphere of pressure (14.7 lb/in.2). This is usually expressed as 760millimeters ofHg or 101.3 pascals.Standard temperature is defined as 273Kelvinorabsolute(whichcorrespondsto0°Celsius).

Charles’sLawJacquesCharles, a French chemist of the early nineteenth century, discoveredthat,whenagasunderconstantpressureisheatedfrom0°Cto1°C,itexpands1/273ofitsvolume.Itcontractsthisamountwhenthetemperatureisdropped1degree to -1°C. Charles reasoned that, if a gas at 0°C was cooled to -273°C(actuallyfoundtobe-273.15°C), itsvolumewouldbezero.Actually,allgasesare converted into liquids before this temperature is reached. By using theKelvinscaletoridtheproblemofnegativenumbers,wecanstateCharles’sLawasfollows:

If the Pressure Remains Constant, theVolumeofaGasVariesDirectlyas theAbsoluteTemperature.Then

Initial =Final atconstantpressure

or

PlotsofVversusTforrepresentativegases.

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Charles’s Law at constant

pressureisadirectproportion.

Graphic relationship—Charles’s Law. The dashed lines representextrapolation of the data into regions where the gas would become liquid orsolid. Extrapolation shows that each gas, if it remained gaseous, would reachzerovolumeat0Kor–273°C.

TYPEPROBLEM:

Thevolumeofagasat20°Cis500.mL.Finditsvolumeatstandardtemperatureifpressureisheldconstant.

Converttemperatures:

20°C=20°+273=293K0°C=0°+273=273K

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Assume dry gases unless otherwisestated.

Ifyouknowthatcoolingagasdecreasesitsvolume,thenyouknowthat500.mLwillhavetobemultipliedbyafraction(madeupoftheKelvintemperatures)thathasasmallernumeratorthanthedenominator.So

Oryoucanusetheformulaandsubstituteknownvalues:

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STP=standard temperatureof273Kstandardpressureof760mmHgor1atmosphere(atm)or105pascals.

ANOTHEREXAMPLE:

Asampleofgasoccupies24Lat175.0K.Whatvolumewouldthegasoccupyat400.0K?

Thetemperatureofthegasisincreased.Charles’sLawpredictsthatthegasvolumewillalsoincrease.So

Thefinalvolumehasincreasedaspredicted.

Boyle’sLaw(PV=k)RobertBoyle,aseventeenthcenturyEnglishscientist,foundthatthevolumeofagas decreases when the pressure on it is increased, and vice versa, when thetemperatureisheldconstant.Boyle’sLawcanbestatedasfollows:

If the Temperature Remains Constant,theVolumeofaGasVariesInverselyasthePressureChanges.Then

P1V1=P2V2ataconstanttemperatureor

PV=k

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Boyle’sLaw

P1V1 = P2V2 temperature is heldconstant

Graphicrelationship—Boyle’sLaw

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Volume vs. pressure for a gas atconstant temperature. This is aninverse proportion. As the pressureincreases by 2, the volume drops by1/2.

TYPEPROBLEM:Giventhevolumeofagasas200.mLat1.05atmpressure,calculatethevolumeofthesamegasat1.01atm.Temperatureisheldconstant.

Ifyouknowthatthisdecreaseinpressurewillcauseanincreaseinthevolume,thenyouknow200.mLmustbemultipliedbyafraction(madeupofthetwopressures)thathasalargernumeratorthanthedenominator.So

Oryoucanusetheformula:

ANOTHEREXAMPLE:Thegasinaballoonhasavolumeof7.5Lat100.kPa.Theballoonisreleasedintotheatmosphere,andthegasinitexpandstoavolumeof11.L.Assumingaconstanttemperature,whatisthepressureontheballoonatthenewvolume?

Thevolumeofthegashasincreased.Boyle’sLawpredictsthatthegaspressurewilldecrease.So

Thefinalpressurehasdecreasedaspredicted.

CombinedGasLawThisisacombinationofthetwoprecedinggaslaws.Theformulaisasfollows:

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In the combined gas law, allsubscripts are1son the left and allsubscriptsare2sontheright.

TYPEPROBLEM:Thevolumeofagasat780.mmpressureand30.°Cis500.mL.WhatvolumewouldthegasoccupyatSTP?

Youagaincanusereasoningtodeterminethekindoffractionsthetemperaturesandpressuresmustbetoarriveatyouranswer.Sincethepressureisgoingfrom780.mmto760.mm,thevolumeshouldincrease.Thefractionmustthenbe Also,sincethetemperatureisgoingfrom30°C(303K)to0°C(273K),thevolumeshoulddecrease;thisfractionmustbe So

Oryoucanusetheformula:

ANOTHEREXAMPLE:

Thevolumeofagasis27.5mLat22.0°Cand0.974atm.Whatwillthevolumebeat15.0°Cand0.993atm?

Usingthecombinedgaslaw,

andsolvingfor

V2=26.3mL

PressureVersusTemperature(Gay-Lussac’sLaw)

At Constant Volume, the Pressure of aGivenMassofGasVariesDirectlywiththeAbsoluteTemperature.Then

TYPEPROBLEM:Asteeltankcontainsagasat27°Candapressureof12.0atms.Determinethegaspressurewhenthetankisheatedto100.°C.

Reasoningthatanincreaseintemperaturewillcauseanincreaseinpressureatconstantvolume,youknowthepressuremustbemultipliedbyafractionthathasalargernumeratorthandenominator.Thefractionmust

be .So

Oryoucanusetheformula:

ANOTHEREXAMPLE:

At120.°C,thepressureofasampleofnitrogenis1.07atm.Whatwillthepressurebeat205°C,assumingconstantvolume?

Usingtherelationshipof:

andsolvingfor

P2=1.30atm

Dalton’sLawofPartialPressures

WhenaGasIsMadeUpofaMixtureofDifferent Gases, the Total Pressure oftheMixture IsEqual to theSumof the

Partial Pressures of the Components;That Is, thePartialPressureof theGasWouldBethePressureoftheIndividualGas If It Alone Occupied the Volume.TheFormulaIs:

Ptotal=Pgas1+Pgas2+Pgas3+…

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Know Dalton’s Law of PartialPressures.

TYPEPROBLEM:Amixtureofgasesat760.mmHgpressurecontains65.0%nitrogen,15.0%oxygen,and20.0%carbondioxidebyvolume.Whatisthepartialpressureofeachgas?

0.650×760.=494mmpressure(N2)0.150×760.=114mmpressure(O2)0.200×760.=152mmpressure(CO2)

Ifthepressurewasgivenas1.0atm,youwouldsubstitute1.0atmfor760.mmHg.Theanswerswouldbe:

0.650×1.0atm=0.650atm(N2)0.150×1.0atm=0.150atm(O2)0.200×1.0atm=0.200atm(CO2)

CorrectionsofPressureCORRECTIONOFPRESSUREWHENAGAS ISCOLLECTEDOVERWATER.Whenagasiscollectedoveravolatileliquid,suchaswater,someofthe water vapor is present in the gas and contributes to the total pressure.

Assuming that the gas is saturatedwithwater vapor at the given temperature,youcanfindthepartialpressureduetothewatervaporinatableofsuchwatervaporvalues.Thisvaporpressure,whichdependsonlyonthetemperature,mustbesubtractedfromthetotalpressuretofindthepartialpressureofthegasbeingmeasured.

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When a gas is collected over water,subtract the water vapor pressure atthe given temperature from theatmospheric pressure to find thepartialpressureofthegas.Pgas=Patm-PH2O

CORRECTION OF DIFFERENCE IN THE HEIGHT OF THE FLUID.Whengasesarecollectedineudiometers(glasstubesclosedatoneend),itisnotalwayspossibletogettheleveloftheliquidinsidethetubetoequalthelevelonthe outside. This deviation of levels must be taken into account whendetermining the pressure of the enclosedgas.There are then twopossibilities:(1)Whenthelevelinsideishigherthantheleveloutsidethetube,thepressureontheinsideisless,bytheheightoffluidinexcess,thantheoutsidepressure.Ifthefluidismercury,yousimplysubtractthedifferencefromtheoutsidepressurereading (also in height ofmercury and in the same units) to get the correctedpressureofthegas.Ifthefluidiswater,youmustfirstconvertthedifferencetoan equivalent height of mercury by dividing the difference by 13.6 (sincemercuryis13.6timesasheavyaswater,theheightexpressedintermsofHgwillbe1/13.6theheightofwater).ThisisshownpictoriallyinFigure21.Again,caremustbetakenthatthisequivalentheightofmercuryisinthesameunitsastheexpressionfortheoutsidepressurebeforeitissubtractedtoobtainthecorrectedpressureforthegasintheeudiometer.(2)Whenthelevelinsideislowerthantheleveloutsidethetube,acorrectionmustbeaddedtotheoutsidepressure.Ifthedifferenceinheightbetweentheinsideandtheoutsideisexpressedintermsofwater, you must take 1/13.6 of this quantity to correct it to millimeters ofmercury.Thisquantity is thenadded to theexpressionof theoutsidepressure,whichmustalsobeinmillimetersofmercury.Ifthetubecontainsmercury,then

the difference between the inside and outside levels is merely added to theoutsidepressuretogetthecorrectedpressurefortheenclosedgas.

Figure21.SamePressureExertedonBothLiquids

TYPEPROBLEM:Hydrogengaswascollectedinaeudiometertubeoverwater.Itwasimpossibletoleveltheoutsidewaterwiththatinthetube,sothewaterlevelinsidethetubewas40.8mmhigherthanthatoutside.Thebarometricpressurewas730.mmofHg.Thewatervaporpressureattheroomtemperatureof29°Cwasfoundinahandbooktobe30.0mm.Whatisthepressureofthedryhydrogen?

Step1:Tofindthetruepressureofthegas,wemustfirstsubtractthewater-leveldifferenceexpressedinmmofHg:

Then730.mm-3.00mm=727mmtotalpressureofgasesintheeudiometer

Step2:Correctingforthepartialpressureduetowatervaporinthehydrogen,wesubtractthevaporpressure(30.0mm)from727mmandgetouranswer:697mm.

IdealGasLawTheprecedinglawsdonotincludetherelationshipofnumberofmolesofagas

to the pressure, volume, and temperature of the gas. A law derived from theKinetic-MolecularTheoryrelatesthesevariables.ItiscalledtheIdealGasLawandisexpressedas

PV=nRT

P,V,andTretaintheirusualmeanings,butnstandsforthenumberofmolesofthegasandRrepresentstheidealgasconstant.

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Knowhowtousetheidealgaslaw,PV=nRT

Boyle’sLawandCharles’sLawareactuallyderivedfromtheIdealGasLaw.Boyle’sLawapplieswhenthenumberofmolesandthetemperatureofthegasare constant. Then inPV=nRT, the number ofmoles, n, is constant; the gasconstant(R)remainsthesame;andbydefinitionTisconstant.Therefore,PV=k.At the initial set of conditionsof a problem,P1V1 = a constant (k). At thesecondsetofconditions,thetermsontherightsideoftheequationareequaltothe same constant, so P1V1 = P2V2. This matches the Boyle’s Law equationintroducedearlier.The same can also be donewithCharles’s Law, becausePV=nRT can be

expressedwiththevariablesontheleftandtheconstantsontheright:

In Charles’s Law the number of moles and the pressure are constant.Substitutingkfortheconstantterm, ,wehave

Theexpressionrelatingtwosetsofconditionscanbewrittenas

TousetheIdealGasLawintheformPV=nRT,thegasconstant,R,mustbe

determined. This can be done mathematically as shown in the followingexample.Onemoleofoxygengaswascollected in the laboratoryata temperatureof

24.0°C and a pressure of exactly 1 atmosphere. The volumewas 24.38 liters.FindthevalueofR.

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Knowtheidealgasconstant

PV=nRT

RearrangingtheequationtosolveforRgives

Substitutingtheknownvaluesontheright,wehave

CalculatingR,weget

OnceRisknown,theIdealGasLawcanbeusedtofindanyofthevariables,giventheotherthree.Forexample,calculatethepressure,at16.0°C,of1.00gramofhydrogengas

occupying2.54liters.RearrangingtheequationtosolveforP,weget

Themolarmass of hydrogen is 2.00 g/mol, so the number ofmoles in thisproblemwouldbe

Substitutingtheknownvalues,wehave

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Remember touseappropriateunits:moles (mol) liters (L) atmosphere(atm)

Calculatingthevalue,wegetP=4.66atm

AnotheruseoftheidealgaslawistofindthenumberofmolesofagaswhenP,T,andVareknown.Forexample,howmanymolesofnitrogengasarein0.38literofgasat0°C

and0.50atmpressure?Rearrangingtheequationtosolveforngives

Changingtemperaturetokelvinsandpressuretoatmospheresgives

T=0°+273=273K

Substitutingintheequation,wehave

=0.0085molofnitrogengas

IdealGasDeviations

Intheuseofthegaslaws,wehaveassumedthatthegasesinvolvedwere“ideal”gases.Thismeansthatthemoleculesofthegaswerenottakingupspaceinthegasvolumeandthatnointermolecularforcesofattractionwereservingtopullthemoleculesclosertogether.Youwillfindthatagasbehaveslikeanidealgasat low pressures and high temperatures, which move the molecules as far aspossible from conditions thatwould cause condensation. In general, pressuresbelow a few atmospheres will cause most gases to exhibit sufficiently idealpropertiesfortheapplicationofthegaslawswithareliabilityofafewpercentorbetter.

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Least deviations occur at lowpressuresandhightemperatures.High deviations occur at highpressuresandverylowtemperatures.

If,however,highpressuresareused,themoleculeswillbeforcedintocloserproximity with each other as the volume decreases until the attractive forcebetween molecules becomes a factor. This factor decreases the volume, andtherefore the PV values at high pressure conditions will be less than thosepredictedbytheIdealGasLaw,wherePVremainsaconstant.Examiningwhatoccurs at very low temperatures creates a similar situation.

Again, the molecules, because they have slowed down at low temperatures,comeintocloserproximitywitheachotherandbegintofeeltheattractiveforcebetweenthem.Thistendstomakethegasvolumesmallerand,therefore,causesthePV to be lower than that expected in the ideal gas situation. Thus, underconditions of very high pressures and low temperatures, deviations from theexpectedresultsoftheidealgaslawwilloccur.

ChapterSummaryThefollowingtermssummarizealltheconceptsandideasthatwereintroducedinthischapter.Youshouldbeabletoexplaintheirmeaningandhowyouwouldusetheminchemistry.Theyappearinboldfacetypeinthischaptertodrawyour

attentiontothem.Theboldfacetypealsomakesiteasierforyoutolookthemupif you need to. You could also use the search or “Google” action on yourcomputer to get a quick and expanded explanation of these terms, laws, andformulas.

atmosphere mercurybarometer standardpressureatmosphericpressure ozone standardtemperaturegreenhouseeffect pascal torrmanometer

Boyle’sLaw(PV=k)constantTCharles’sLaw

CombinedGasLaw

Dalton’sLawofPartialPressures

(constantT)

Graham’sLawIdealGasLawKinetic-MolecularTheory

InternetResourcesOnline content that reinforcesmajor concepts discussed in this chapter canbefoundatthefollowingInternetaddressiftheyarestillavailable.Somemayhavebeenchangedordeleted.Kinetic-MolecularTheorywww.schoolforchampions.com/science/matter_kinetic_energy_theory.htmThissitereviewsthebasictenetsofKinetic-MolecularTheory.TheIdealGasLawhttp://jersey.uoregon.edu/vlab/Piston/index.htmlThissiteoffersanexperimentalexercisetointeractvirtuallywiththebehaviorofgases.GasLawProblems

http://www.sciencebugz.com/chemistry/cprbogas.htmThissitegivesyouanopportunitytopracticesolvinggaslawproblems

PracticeExercises1.ThemostabundantelementinEarth’scrustis

(A)sodium(B)oxygen(C)silicon(D)aluminum

2.Acompoundthatcanbedecomposedtoproduceoxygengasinthelabis

(A)MnO2

(B)NaOH(C)CO2

(D)KClO3

3.Intheusuallaboratorypreparationequationforthereactioninquestion2,whatisthecoefficientofO2?

(A)1(B)2(C)3(D)4

4.Inthegraphicrepresentationoftheenergycontentsofthereactantsandtheresultingproductsinanexothermicreaction,theenergycontentwouldbe

(A)higherforthereactants(B)higherfortheproducts(C)thesameforboth(D)impossibletodetermine

5.Theprocessofseparatingcomponentsofamixturebymakinguseofthedifferenceintheirboilingpointsiscalled

(A)destructivedistillation(B)displacement(C)fractionaldistillation(D)filtration

6.Whenoxygencombineswithanelementtoformacompound,theresultingcompoundiscalled

(A)asalt(B)anoxide(C)oxidation(D)anoxalate

7.Accordingtotheactivitychartofmetals,whichmetalwouldreactmostvigorouslyinadiluteacidsolution?

(A)zinc(B)iron(C)aluminum(D)magnesium

8.Graham’sLawrefersto

(A)boilingpointsofgases(B)gaseousdiffusion(C)gascompressionproblems(D)volumechangesofgaseswhenthetemperaturechanges

9.When200millilitersofagasatconstantpressureisheated,itsvolume

(A)increases(B)decreases(C)remainsunchanged

10.When200millilitersofagasatconstantpressureisheatedfrom0°Cto100°C,thevolumemustbemultipliedby

(A)0/100(B)100/0(C)273/373(D)373/273

11.Ifyouwishtofindthecorrectedvolumeofagasthatwasat20°Cand1atmospherepressureandconditionswerechangedto0°Cand0.92atmospherepressure,bywhatfractionswouldyoumultiplytheoriginalvolume?

(A)

(B)

(C)

(D)

12.Whenthelevelofmercuryinsideagastubeishigherthanthelevelinthereservoir,youfindthecorrectpressureinsidethetubebytakingtheoutsidepressurereadingand?thedifferenceintheheightofmercury.

(A)subtracting(B)adding(C)dividingby13.6(D)doingboth(c)and(a)

13.Ifwateristheliquidinquestion12insteadofmercury,youcanchangetheheightdifferencetoanequivalentmercuryexpressionby

(A)dividingby13.6(B)multiplyingby13.6(C)adding13.6(D)subtracting13.6

14.Standardconditionsare

(A)0°Cand14.7mm(B)273Kand760mmHg(C)273°Cand760mmHg(D)4°Cand7.6mmHg

15.Whenagasiscollectedoverwater,thepressureiscorrectedby

(A)addingthevaporpressureofwater(B)multiplyingbythevaporpressureofwater

(C)subtractingthevaporpressureofwateratthattemperature(D)subtractingthetemperatureofthewaterfromthevaporpressure.

16.At5.00atmospherespressureand70°Chowmanymolesarepresentin1.50litersofO2gas?

(A)0.036(B)0.266(C)0.536(D)0.103

Directions: Every set of the given lettered choices below refers to thenumberedquestionsimmediatelybelowit.Foreachnumbereditem,choosetheoneletteredchoicethatfits itbest.Everychoiceinasetmaybeusedonce,morethanonce,ornotatall.

Questions17–20refertothefollowinggraphs:

17.WhichisagraphicdepictionofBoyle’sLaw?

18.WhichisagraphicdepictionofCharles’sLaw?

19.Whichisagraphicdepictionoftherelationshipofthepressureofagivenvolumeofgaswiththeabsolutetemperature?

20.Whichgraphshowsthedistributionofmoleculeswithrespecttotheirkineticenergyatdifferenttemperatures?

AnswersandExplanations1.(B)OxygenisthemostabundantelementinEarth’scrust,with21%ofitscomposition.

2.(D)KClO3canbedecomposedwithheattoformKClandO2.

3.(C)Theequationis2KClO3(s)→2KCl(s)+3O2(g)

4.(A)Sinceenergyisgivenoffinanexothermicreaction,theheatcontentofthereactantswouldbehigherthantheproducts.

5.(C)Fractionaldistillationcanseparateliquidsofdifferentboilingpoints.

6.(B)Oxygencompoundsformedincombinationreactionsarecalledoxides.

7.(D)Magnesium,whichisthemostactiveofthegivenmetals,willreacttoreleasehydrogen.

8.(B)Graham’sLawreferstogaseousdiffusionoreffusion.

9.(A)Whenconfinedgasesataconstantpressureareheated,theyexpand.

10.(D)Thetemperaturemustbechangedtoabsolutetemperaturebyadding273totheCelsiusreadings.

11.(C)Sincethetemperatureisdecreasing,thevolumemustdecreasewiththetemperaturefraction,and,becausethepressureisdecreasing,thevolumemustincrease.Thecorrectanswerdoesthis.

12.(A)Thelevelishigherbecausethepressureinsidethetubeislessthanoutside.Youmustsubtracttheheightinsidethetubefromtheoutsidepressure.

13.(A)Ifwateristheliquid,youmustdivideby13.6tochangetheheighttotheequivalentheightofmercury.

14.(B)Theonlycorrectindicationofstandardconditionsis(B).Itisusuallystatedas273Kand760mmHg.(Note:“mm”and“torr”areinterchangeable.)

15.(C)Becausethevaporpressureofwaterisapartofthepressurereading,itmustbesubtractedtogettheatmosphericpressure.

16.(B)Usingthegeneralgaslaw,PV=nRT,convert70°CtoKbyadding273=343K.Solvingforn,youget

17.(C)Boyle’sLawisaninverserelationship.Asthepressureincreases,thevolumedecreases,asshownbythegraph.

18.(A)Charles’sLawisadirectrelationship.Asthetemperatureincreases,thevolumeincreases.

19.(A)Therelationshipofpressuretoabsolutetemperaturewhilethevolumeisheldconstantisadirectone.Asthetemperatureonagivenvolumeincreases,thepressurewillincrease.

20.(D)Thegraphsin(D)showthedistributionsofthekineticenergyofmoleculesattwodifferenttemperatures.

CHAPTER6

Stoichiometry(ChemicalCalculations)andtheMoleConcept

TheseskillsareusuallytestedontheSATSubjectTestinChemistry.Youshouldbeableto...•Usethemoleconcepttofindthemolarmassofformulasandofmonoatomicanddiatomicmolecules,andhowgasvolumesarerelatedtomolarmass.

•SolvestoichiometricproblemsinvolvingGay-Lussac’sLaw,density,mass–volumerelation,mass–massproblems,volume–volumeproblems,problemswithalimitingreactant(excessofonereactant),andfindingthepercentyield.

This chapter will review and strengthen these skills. Be sure to do thePracticeExercisesattheendofthechapter.

Thischapterdealswiththesolvingofavarietyofchemistryproblems,whichisoften referred to as stoichiometry. Solving problems should be done in anorganized manner, and it would be to your advantage to go back to theIntroductiontothisbookandreviewthesectioncalled,“HowCanYouImproveYourProblemSolvingSkills?”Itdescribesawell-plannedmethodforattackingtheprocessofsolvingproblemsthatyouwillfindhelpfulinthischapter.Two or three methods of solving the problems in this chapter are usually

given. Itwouldbewiseonyourpart to learn themolemethod, theproportionmethod,and the factor-labelmethod (also referred toasdimensionalanalysis),so thatyouhavemore toolsavailableforsolvingproblems.Remember thatnomatter which method you use, you should still use the estimation process toverifytheplausibilityoftheanswer.

THEMOLECONCEPTProviding a name for a quantity of things taken as a whole is common in

everyday life.Someexamplesareadozen,agross, anda ream.Eachof theserepresentsaspecificnumberofitemsandisnotdependentonthecommodity.Adozeneggs,oranges,orbananaswillalwaysrepresent12items.

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Know Avogadro’s number and itsuse.

Inchemistrywehaveaunitthatdecribesaquantityofparticles.Itiscalledthemole (sometimes abbreviated asmol ). A mole is 6.02 × 1023 particles. Theparticlescanbeatoms,molecules,ions,electrons,andsoforth.Becauseparticlesaresosmallinchemistry,themoleisaveryconvenientunit.Thenumber6.02×1023isoftenreferredtoasAvogadro’snumberinhonoroftheItalianscientistwhosehypothesisledtoitsdetermination.In 1811, Amedeo Avogadro made a far-reaching scientific assumption

(hypothesis)thatalsobearshisname.Hestatedthatequalvolumesofdifferentgasescontainequalnumbersofmoleculesatthesamepressureandtemperature.The statement is called Avogadro’s Law. It means that, under the sameconditions,thenumberofmoleculesofhydrogenina1-litercontainerisexactlythesameasthenumberofmoleculesofcarbondioxideoranyothergasina1-litercontainereventhoughtheindividualmoleculesofthedifferentgaseshavedifferentmasses and sizes.Becauseof the substantiationof this hypothesis bymanydatasinceitsinception,itisoftenreferredtoasAvogadro’sLaw.

MOLARMASSANDMOLESWhentheformulamassofanioniccompoundisdeterminedbytheadditionofits component relative atomicmasses and expressed in grams, it is called themolarmass.

EXAMPLE:FindthemolarmassofCaCO3.

Themolarmassisequivalenttothemassof1moleofthatcompoundexpressedingrams.

ANOTHEREXAMPLE:Findthemassof1moleofKAl(SO4)2·12H2O.

TRYTHESEPROBLEMS:Findthemolecularmassorformulamassofeachofthefollowing:

1.HNO3Ans.63g/mol2.C6H10O5Ans.162g/mol3.H2SO4Ans.98g/mol4.KClAns.74.5g/mol5.C12H22O11Ans.342g/mol

Insomecases,theremaybeaquestionofthemassof1moleofanelementifyouarenottoldspecificallywhatisreferredto—thesingleatomsoramolecularstate.Anexampleofthissituationmayarisewithhydrogenandotherelementsthatformdiatomicmolecules.Ifyouareaskedthemassof1moleofhydrogen,youcouldsayitis1gramifyouaredealingwithsingleatomsofhydrogen.This1moleofhydrogenatomswouldcontain6.02×1023atoms.Inasimilarfashion,1moleofhydrogenmolecules(H2)wouldhaveamolarmassof2grams.This1mole of hydrogenmoleculeswould contain 6.02 × 1023 molecules and, sinceeachmoleculeiscomposedoftwoatoms,12.04×1023atoms.The other elements that exist as diatomic molecules are oxygen, nitrogen,

fluorine,chlorine,bromine,iodine,andastatine.Examples:

1.Whatisthemassof1moleofoxygen?Answer:Sincetheatomicmassofoxygenis16gramsandthemoleculeis

diatomic,2×16.0grams=32.0grams.

2.Whatisthemassofonemoleculeofoxygen?Answer:Thereare6.02×1023moleculesin1moleofthisgas.32.0grams÷

6.02×1023molecules=5.32×10−23gram.

3.Whatisthemassof1moleofoxygenatoms?Answer:Without the diatomicmolecule structure, themass of onemole of

oxygenatomsexpressedingramsistheanswer.Thatis16.0g/mol.

4.Whatisthemassofoneatomofoxygen?Answer:Theatomicmolarmass,16.0grams,isdividedby6.02×1023.This

gives2.66×10−23gram.

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Know how to use theserelationships!

Ifyougavethesameanswertothefirsttwoquestions,youareconfusedaboutthemoleconcept.Tosaythatamoleculeofoxygengashasthesamemassasamoleofoxygengasisthesameassayingthatanapplehasthesamemassasadozenapples.

MOLERELATIONSHIPSBecause themole isusedoften in chemistry toquantify thenumberof atoms,molecules,andseveralotheritems,itisimportanttoknowtherelationshipsthatexistandhowtomovefromonetoanother.Thefollowingsummarizesanumberoftheserelationships:

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Know how to use these mole

relationships.Theywillbeneededtodostoichiometryproblems.

Whendealingwithelements—Molesofanelement×molarmass(atomic)=massoftheelementMassofanelement/molarmass(atomic)=molesoftheelement

Whendealingwithcompounds—Molesofacompound×molarmass(molecular)=massofthecompoundMassofacompound/molarmass(molecular)=molesofthecompound

Whendealingwiththemoleculesofacompound—Molesofmolecules×6.02×1023=numberofmoleculesNumberofmolecules/6.02×1023=molesofmolecules

Whendealingwiththeatomsofelements—Molesofatoms×6.02×1023=numberofatomsNumberofatoms/6.02×1023=molesofatoms

GASVOLUMESANDMOLARMASSBecause the volume of a gas may vary depending on the conditions oftemperature and pressure, a standard is set for comparing gases. As stated inChapter 5, the standard conditions of temperature and pressure (abbreviatedSTP)are273Kand760mmofmercurypressure.The molecular mass of a gas expressed in grams and under standard

conditionsoccupies22.4 liters.This is an important relationship to remember!The 22.4 liters is referred to as the gram-molecular volume (gmv) or molarvolume.Twoscientistsareassociatedwiththisrelationship.Gay-Lussac’sLawstatesthat,whenonlygasesareinvolvedinareaction,the

volumesofthereactinggasesandthevolumesofthegaseousproductsareinasmall-whole-number ratio to each other. This law may be illustrated by thefollowingcases:

Example1:H2(g)+Cl2(g)→2HCl(g)

Thisbalancedequationshowsthat1vol.hydrogen+1vol.chlorine=2vols.hydrogenchloride

Example2:2H2(g)+O2(g)→2H2O(g)

This balanced equation shows that 2 vols. hydrogen + 1 vol.oxygen=2vols.steam

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Know Gay-Lussac’s Law ofcombininggases.

Avogadro’sLaw,whichexplainsGay-Lussac’s,statesthatequalvolumesofgases under the same conditions of temperature and pressure contain equalnumbersofmolecules.Thismeansthat1moleofanygasatSTPoccupies22.4liters,so:

32gO2atSTPoccupies22.4liters2gH2atSTPoccupies22.4liters44gCO2atSTPoccupies22.4liters2O2(2molesO2)=64g=44.8litersatSTP3H2(3molesH2)=6g=67.2litersatSTP

DENSITYANDMOLARMASSSincethedensityofagasisusuallygiveningrams/literofgasatSTP,wecanusethemolarvolumetomolarmassrelationshiptosolvethefollowingtypesofproblems.

EXAMPLE1:Findthemolarmassofagaswhenthedensityisgivenas1.25grams/liter.

Becauseitisknownthat1moleofagasoccupies22.4litersatSTP,wecansolvethisproblembymultiplyingthemassof1literby22.4liters/mole.

Eveniftheweightgivenisnotfor1liter,thesamesetupcanbeused.

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REMEMBERForadrygasatSTP,themassof1liter×22.4=themolarmassofthegas.

EXAMPLE2:If3.00litersofagasweighs2.00grams,findthemolarmass.Solution:

Youcanalsofindthedensityofagasifyouknowthemolarmass.Sincethemolarmassoccupies22.4litersatSTP,dividingthemolarmassby22.4literswillgiveyouthemassperliter,orthedensity.

EXAMPLE3:FindthedensityofoxygenatSTP.Solution:Oxygenisdiatomicinitsmolecularstructure.O2=molarmassof2×16.0or32.0g/mol32.0g/moloccupies22.4L.Therefore

Youcanfindthedensityofagas,then,bydividingitsmolarmassby22.4liters.

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For a dry gas at STP,

MASS–VOLUMERELATIONSHIPSAtypicalmass-volumeproblem:

EXAMPLE1:Howmanylitersofoxygen(STP)canyoupreparefromthedecompositionof42.6gramsofsodiumchlorate?

This problem can also be solved usingmethods other than the proportionmethodshownabove.

Anothermethodtoproceedfromstep3iscalleddimensionalanalysis,alsoreferred to as the factor-label method. The reasoning is this: Because theequation shows that213gramsof reactantproduces67.2 litersof the requiredproduct,multiplyingthegivenamountbythisequality(sothat theunitsof theanswerwillbecorrect)willgivethesameanswerasabove.Thenstep4wouldbe:

Stillanothermethodofsolvingthisproblemiscalledthemolemethod.Steps1and2arethesame.Thenstep3isasfollows:

EXAMPLE2:FindtheweightofCaCO3neededtoproduce11.2LCO2whenthecalciumcarbonateisreactedwithhydrochloricacid.

PROPORTIONMETHOD:

FACTOR-LABELMETHOD:

MOLEMETHOD:

TRYTHESEMASS-VOLUMEPRACTICEPROBLEMS:1.Whatmassofwatermustbeelectrolyzedtoobtain20.0litersofoxygenatSTP?

Ans.32.2g*

2.Howmanygramsofaluminumwillbecompletelyoxidizedby44.8litersofoxygenatSTP?

Ans.72.0g*

______*Answersexplainedattheendofthischapter.

MASS–MASSPROBLEMSAtypicalproblemconcerningjustmassrelationshipsisasfollows:

EXAMPLE1:Whatmassofoxygencanbeobtainedfromheating100.gramsofpotassiumchlorate?

1ststep.Writethebalancedequationforthereaction.

2KClO3→2KCl+3O2

2ndstep.Writethegivenquantityandtheunknownquantityabovetheappropriatesubstances.

3rd step. Calculate the equation mass for each substance that hassomething

indicatedaboveit,andwritetheresultsunderthesubstances.Notethattheunitsaboveandbelowmustmatch.

TIP

Putwhatisgivenabovetheequation.Putthecalculatedamountbelow.Theunitsmustmatch!

USINGTHEPROPORTIONMETHOD:4thstep.Formtheproportion.

5thstep.Solveforx.

x=39.3gofO2

USINGTHEFACTOR-LABELMETHOD:Fromthe3rdsteponyouwouldproceedasfollows:

4thstep.The equation indicates that 245 gKClO3 yields 96 g ofO2. Thereforemultiplying the given quantity by a factor made up of these twoquantitiesarrangedappropriatelyso that theunitsof theanswer remainuncanceledwillgivetheanswertotheproblem.

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After you cancel all similar units

above and below, you should haveremainingtheunitsforyouranswer.

USINGTHEMOLEMETHOD:Tosolvethisproblemyouwouldproceedasfollowsfromthe2ndstep:

EXAMPLE2:Whatmassofpotassiumhydroxideisneededtoneutralize20.0gramsofsulfuricacid?

USINGTHEPROPORTIONMETHOD:

USINGTHEFACTOR-LABELMETHOD:

USINGTHEMOLEMETHOD:

TRYTHESEMASS–MASSPRACTICEPROBLEMS:3.Whatmassofmanganesedioxideisneededtoreactwithanexcessofhydrochloricacidsothat100.gramsofchlorineisliberated?

Ans.:122.5g*

4.A20.0gramsampleofMgisburnedin20.0gramsofO2.HowmuchMgOisformed?(Hint:Determinewhichisinexcess.)

Ans.33.3g*

VOLUME–VOLUMEPROBLEMSThistypeofprobleminvolvesonlyvolumeunitsandthereforecanmakeuseofGay-Lussac’s Law: “When gases combine, they combine in simple whole-numberratios.”Thesesimplenumbersarethecoefficientsoftheequation.

Atypicalproblemconcerningjustvolumerelationshipsisasfollows:

TIP

KnowGay-Lussac’sLaw.

EXAMPLE1:What volume of NH3 is produced when 22.4 liters of nitrogen are made tocombinewithasufficientquantityofhydrogenundertheappropriateconditions?

USINGTHEPROPORTIONMETHOD:

USINGTHEFACTOR-LABELMETHOD:Fromthe2ndsteponyouwouldproceedasfollows:

USINGTHEMOLEMETHOD:Tosolvethisproblemyouwouldproceedasfollows:

EXAMPLE2:WhatvolumeofSO2willresultfromthecompleteburningof

puresulfurin8litersofoxygenuntilalltheoxygenisused?

USINGTHEPROPORTIONMETHOD:

USINGTHEFACTOR-LABELMETHOD:

USINGTHEMOLEMETHOD(NOTREALLYPRACTICALINTHISCASE):

TRYTHESEVOLUME-VOLUMEPRACTICEPROBLEMS:5.Howmanylitersofhydrogenarenecessarytoreactwithsufficientchlorinetoproduce12litersofhydrogenchloridegas?

Ans.6LH2*

6.Howmanylitersofoxygenwillbeneededtoburn100litersofcarbonmonoxide?

Ans.50LO2*

PROBLEMSWITHANEXCESSOFONEREACTANTORALIMITINGREACTANTIt will not always be true that the amounts given in a particular problem are

exactlyintheproportionrequiredforthereactiontouseupallofthereactants.Inotherwords,attimessomeofonereactantwillbeleftoveraftertheotherhasbeenusedup.Thisissimilartothesituationinwhichtwoeggsarerequiredtomixwithonecupofflourinaparticularrecipe,andyouhavefoureggsandfourcupsofflour.

TIP

The paragraph describes a practicalexampleofa“limitingreactant.”

Sincetwoeggsrequireonlyonecupofflour,foureggscanuseonlytwocupsofflourandtwocupsofflourwillbeleftover.

TIP

Remember this recipe analogy tosolvelimitingreactantquestions!

A chemical equation is very much like a recipe. Consider the followingequation:

Zn(s)+2HCl(l)→ZnCl2(aq)+H2(g)

Ifyouaregiven65gramsofzincand65gramsofHCl,howmanygramsofhydrogen gas can be produced?Which reactantwill be left over?Howmanygramsofthisreactantwillnotbeconsumed?

The given quantities are above the equation, and the equation masses aregivenbeneath.Tosolveforthegramsofhydrogengas,thelimitingreactantmustbedetermined.

2ndstep.Comparethegivenquantitieswiththeequationrequirements.

Knowingthatittakes65gramsofzinctoreactwith73gramsofhydrochloricacid, it is reasonable to surmise that, since there are only 65 grams ofhydrochloric acid, not all of the 65 grams of zinc can be used. The limitingfactorwillbetheamountofhydrochloricacid.

3rdstep.Solveforthequantityofproductthatwillbeproducedusingtheamountofthelimitingfactor.

Nowthatweknowthatthelimitingfactoristheamountofhydrochloricacid(65 g), the equation can be solved. This means that the proportion is set upignoringthe65gramsofzinc.

Solvingforx,wegetx=1.78gramsor1.8gramsofhydrogenproduced.

Thisgivestheproportion:

PERCENTYIELDOFAPRODUCTInmoststoichiometricproblems,weassumethattheresultsareexactlywhatwewouldtheoreticallyexpect.Inreality,theresultingtheoreticalyieldisrarelytheactualyield.Whytheactualyieldofareactionmaybelessthanthetheoreticalyield occurs for many reasons. Some of the product is often lost during thepurificationorcollectionprocess.Chemistsareusuallyinterestedintheefficiencyofareaction.Theefficiency

isexpressedbycomparingtheactualandthetheoreticalyields.

The percent yield is the ratio of the actual yield to the theoretical yield,multipliedby100%.

EXAMPLE:Quicklime,CaO,istobepreparedbyroasting2.00×103goflimestone,CaCO3,accordingtothefollowingreaction.However,theactualyieldofCaOis1.05×103g.Whatisthepercentofyield?

Thereactionis:

CaCO3(s)→CaO(s)+CO2(g)

Thepercentyieldisfoundbyusingtheaboveformulaandinsertingtheactualandtheoreticalyields.

Tofindthetheoreticalyield,yousolvethefollowing:

AnswersandExplanationstoEmbeddedChapterPracticeProblemsAftereach typeofproblemin thischapter thereareseveralproblems tosolve;thereforethechapterreviewdoesnotincludeproblems.Theanswerexplanationsfortheproblemspreviouslypresentedaregivenbelow.

1.

Calculatetheequationmassandvolumesothattheunits

matchtheonesabovetheequation.

Then

Usingthemolemethod:

Themolerelationshipintheequationis:2molesH2O→2H2+1moleO2

Because1molH2O=18g/mol

2.

Calculatetheequationmassandvolumesothattheunitsmatchtheonesabovetheequation.

Usingthemolemethod:

Thebalancedequationshowsthat4molAlneeded3molO2.Then

Becausethereis27gin1molAl,

3.Theequation:

Then

Usingthemolemethod:

Thebalancedequationshowsthat1molMnO2needed1molCl2.Then

Becausethereis(54.9+32.0)or86.9gin1molMnO2,

4.Theequation:

Comparingtheamountsneededbelowtheequation,youseethatyouneedmoreMgthanO2.Therefore,theamountofMgwillbethelimitingfactorbecauseitwillbeusedupfirst.BecausetheequationmassesindicateyoumusthavemoreMgthanO2,thereisanexcessofoxygen.

Usingthemolemethod:

Thebalancedequationshowsthat2molMgforms2molMgO.Then

Becausethereis(24+16)or40.gofMgOin1molMgO,

5.Theequation:

Setuptheproportionusingthecoefficientsofthesubstancesthathavesomethingindicatedabovethemasdenominators.Gay-Lussac’sLawsaysthatwithreactinggasesyoucanusethecoefficientsofthebalancedequationtosolvetheproblem.

6.Theequation:

Setuptheproportionusingthecoefficientsofthesubstancesthathavesomethingindicatedabovethemasdenominators.Hereagain,becausethereactionisofgases,youcanusethecoefficientsofthebalanceequationtosetuptheproportion.

ChapterSummaryThefollowingtermssummarizealltheconceptsandideasthatwereintroducedinthischapter.Youshouldbeabletoexplaintheirmeaningandhowyouwouldusetheminchemistry.Theyappearinboldfacetypeinthischaptertodrawyourattentiontothem.Theboldfacetypealsomakesiteasierforyoutolookthemup

if you need to. You could also use the search or “Google” action on yourcomputer to get a quick and expanded explanation of these terms, laws, andformulas.

dimensionalanalysis mole Avogadro’sLaw

molarmass STPAvogadro’snumber=(6.02×1023)

molarvolume Gay-Lussac’sLawDensityofgases

InternetResourcesOnline content that reinforcesmajor concepts discussed in this chapter canbefound at the following Internet addresses if they are still available.Somemayhavebeenchangedordeleted.TheMoleConcepthttp://web.clark.edu/nfattaleh/classes/100/LectureNotes/Ch6.pdfThissitegivesageneralreviewofthemoleconceptandsomesampleproblemstomakeunderstandingofthemoleconcepteasier.Stoichiometryhttp://www.chemtutor.com/mols.htmThissitegivesagoodreviewofsolvingtypicalstoichiometryproblems.

PracticeExercises

Often there are some equations on a chemistry test to either complete orcompleteandbalance.Thefollowing list includesrepresentativeequations thatyoushouldbecapableofcompletingandbalancing:

1.zinc+sulfuricacid→

2.iron(III)chloride+sodiumhydroxide→iron(III)hydroxide(s)+sodiumchloride

3.aluminumhydroxide+sulfuricacid→aluminumsulfate+water

4.potassium+water→

5.magnesium+oxygen→

6.silvernitrate+copper→copper(II)nitrate+silver(s)

7.magnesiumbromide+chlorine→magnesiumchloride+bromine

AnswersandExplanationsBelowthewordequationsarethecompletebalancedequations.

1.zinc+sulfuricacid→zincsulfate+hydrogen(g)Zn+H2SO4→ZnSO4+H2(g)

2.FeCl3+3NaOH→Fe(OH)3(s)+3NaCl

3.2Al(OH)3+3H2SO4→Al2(SO4)3+6H2O

4.potassium+water→potassiumhydroxide+hydrogen(g)2K+2H2O→2KOH+H2(g)

5.magnesium+oxygen→magnesiumoxide2Mg+O2→2MgO

6.2AgNO3+Cu→Cu(NO3)2+2Ag(s)

7.MgBr2+Cl2→MgCl2+Br2

CHAPTER7

Liquids,Solids,andPhaseChanges

TheseskillsareusuallytestedontheSATSubjectTestinChemistry.Youshouldbeableto…•Explain,usingagraph,thedistributionofthekineticenergyofmoleculesofaliquidatdifferenttemperatures.

•Describethestatesofmatterandwhatoccurswhenasubstancechangesstate.•Definecriticaltemperatureandpressure.•Analyzeaphasediagramandthetriplepoint.•Solvewatercalorimetryproblemsthatincludechangesofstate.•Explainthepolarityofthewatermoleculeandhydrogenbonding.•Solvesolubilityproblems,concentrationproblems,andchangesinboilingpoint/freezingpointofwaterproblems.

•Describethecontinuumofwatermixturesincludingsolutions,colloids,andsuspensions.

This chapter will review and strengthen these skills. Be sure to do thePracticeExercisesattheendofthechapter.

Liquids and solids each have their own properties, including intermolecularinteractions,surfacetension,andmore.Infact,oneveryimportantcompound—water—hasdistinctpropertiesnecessaryforlifetoexistonthisplanet.

LIQUIDSImportanceofIntermolecularInteractionA liquid can be described as a form ofmatter that has a definite volume andtakestheshapeofitscontainer.Inaliquid,thevolumeofthemoleculesandtheintermolecular forces between them are much more important than in a gas.Whenyouconsiderthatinagasthemoleculesconstitutefarlessthan1%ofthetotalvolume,whileintheliquidstatethemoleculesconstitute70%ofthetotal

volume, it is clear that in a liquid the forces between molecules are moreimportant.Becauseofthis

Figure22.DistributionoftheKineticEnergyofMolecules

decreasedvolumeandincreasedintermolecularinteraction,aliquidexpandsandcontracts only very slightly with a change in temperature and lacks thecompressibilitytypicalofgases.

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Anincreaseintemperatureincreasesthe average kinetic energy of themolecules.

KineticsofLiquidsEventhoughthevolumeofspacebetweenmoleculeshasdecreased ina liquidandthemutualattractionforcesbetweenneighboringmoleculescanhavegreateffects on themolecules, they are still inmotion.Thismotion can be verifiedunder a microscope when colloidal particles are suspended in a liquid. Theparticles’zigzagpath,calledBrownianmovement, indicatesmolecularmotionandsupportstheKinetic-MolecularTheory.Increasesintemperatureincreasetheaveragekineticenergyofmoleculesand

the rapidity of their movement. This is shown graphically in Figure 22. The

moleculesinthesampleofcoldliquidhave,ontheaverage,lesskineticenergythanthoseinthewarmersample.HencethetemperaturereadingT1willbelessthan the temperature readingT2. If a particularmolecule gains enough kineticenergy when it is near the surface of a liquid, it can overcome the attractiveforces of the liquid phase and escape into the gaseous phase. This is called achangeofphase.Whenfast-movingmoleculeswithhighkineticenergyescape,theaverageenergyoftheremainingmoleculesislower;hencethetemperatureislowered.

ViscosityViscosityisthefrictionorresistancetomotionthatexistsbetweenthemoleculesof a liquidwhen theymove past each other. It is logical that the stronger theattractionbetweenthemoleculesofaliquid,thegreateritsresistancetoflow—and thus the greater its viscosity. The viscosity of a liquid depends on itsintermolecular forces.Because hydrogen bonds are such strong intermolecularforces, liquids with hydrogen bonds tend to have high viscosities. Water, forexample, is stronglyhydrogenbondedandhas a relativelyhighviscosity.Youmay have noticed how fast liquids with low viscosity, such as alcohol andgasoline,flow.

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More viscous liquids move moreslowly.

SurfaceTensionMolecules at the surface of a liquid experience attractive forces downward,towardtheinsideoftheliquid,andsideways,alongthesurfaceoftheliquid.Onthe other hand, molecules in the center of the liquid experience uniformlydistributedattractiveforces.This imbalanceof forcesat thesurfaceofa liquidresultsinapropertycalledsurfacetension.Theunevenforcesmakethesurfacebehaveasifithadatightfilmstretchedacrossit.Dependingonthemagnitudeof the surface tensionof the liquid, the film isable to support theweightofasmallobject,suchasarazorbladeoraneedle.Surfacetensionalsoexplainsthebeadingofraindropsontheshinysurfaceofacar.

CapillaryActionCapillary action, the attraction of the surface of a liquid to the surface of asolid,isapropertycloselyrelatedtosurfacetension.Aliquidwillrisequitehighinaverynarrowtubeifastrongattractionexistsbetweentheliquidmoleculesandthemoleculesthatmakeupthesurfaceofthetube.Thisattractiontendstopull the liquidmolecules upward along the surface against the pull of gravity.Thisprocesscontinuesuntil theweightof the liquidbalances thegravitationalforce. Capillary action can occur between water molecules and paper fiber,causing thewatermolecules to riseup thepaper.Whenawater soluble ink isplacedon thepaper, the inkmovesup thepaperand separates into itsvariouscolored components. This separation occurs because the water and the paperattract themolecules of the ink components differently. These phenomena areusedintheseparationprocessofpaperchromatography,asshowninthepaperchromatographyexperimenton.Capillaryactionisatleastpartlyresponsibleforthe transportation of water from the roots of a plant to its leaves. The sameprocess is responsible for the concave liquid surface, called ameniscus, thatformsinatesttubeorgraduatedcylinder.

PHASEEQUILIBRIUMFigure23showswaterinacontainerenclosedbyabelljar.Observationofthisclosedsystemwouldshowaninitialsmalldropinthewaterlevel,butaftersometime the level would become constant. The explanation is that, at first, moreenergeticmoleculesnear thesurfaceareescapinginto thegaseousphasefasterthan some of the gaseous water molecules are returning to the surface andpossiblybeingcaughtbytheattractiveforcesthatwillretainthemintheliquidphase.Aftersometimetheratesofevaporationandcondensationequalize.Thisisknownasphaseequilibrium.

Figure23.ClosedSysteminDynamicEquilibrium

Inaclosedsystemlikethis,whenopposingchangesaretakingplaceatequalrates,thesystemissaidtohavedynamicequilibrium.Athighertemperatures,since the number of molecules at higher energies increases, the number ofmoleculesintheliquidphasewillbereducedandthenumberofmoleculesinthegaseous phase will be increased. The rates of evaporation and condensation,however,willagainbecomeequal.

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MoreaboutequilibriumisdiscussedinChapter9.

Thebehaviorof thesystemdescribedabove illustrateswhat isknownasLeChâtelier’sPrinciple .Itisstatedasfollows:Whenasystematequilibriumisdisturbed by the application of a stress (a change in temperature, pressure, orconcentration),itreactssoastominimizethestressandattainanewequilibriumposition.Inthediscussionabove,ifthe20°Csystemisheatedto30°C,thenumberof

gasmoleculeswill be increasedwhile the number of liquidmoleculeswill bedecreased:

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REMEMBERLe Châtelier’s Principle. It willoccuragaininChapter10.

Theequationshiftstotheright(anysimilarsystemthatisendothermicshiftsto therightwhentemperature is increased)untilequilibriumisreestablishedatthenewtemperature.Themoleculesinthevaporthatareinequilibriumwiththeliquidatagiven

temperature exert a constant pressure. This is called the equilibrium vaporpressureatthattemperature.

BOILINGPOINTThevaporpressure-temperaturerelationcanbeplottedonagraphforaclosed

system.(SeeFigure24.)Whenaliquidisheatedinanopencontainer,theliquidand vapor are not in equilibrium and the vapor pressure increases until itbecomesequaltothepressureabovetheliquid.Atthispointtheaveragekineticenergyofthemoleculesissuchthattheyarerapidlyconvertedfromtheliquidtothevaporphasewithin the liquidaswell as at the surface.The temperatureatwhich this occurs is known as the boiling point. Notice that in this graph,water’snormalboilingpointisat760mmHgpressureand100°Ctemperature.

Figure24.VaporPressure-TemperatureRelationshipforCarbonTetrachloride

andWater

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Boilingpointisdefinedasthepointatwhich the liquid’svaporpressureequalstheatmosphericpressure.

CRITICALTEMPERATUREANDPRESSUREThereareconditionsforparticularsubstanceswhenitisimpossiblefortheliquidor gaseous phase to exist. Since the kinetic energy of a molecular system isdirectlyproportionaltotheKelvintemperature,itislogicaltoassumethatthereisatemperatureatwhichthekineticenergyofthemoleculesissogreatthattheattractive forces between molecules are insufficient for the liquid phase toremain. The temperature above which the liquid phase of a substance cannotexist is called its critical temperature. Above its critical temperature, no gascan be liquefied regardless of the pressure applied. The minimum pressurerequiredtoliquefyagasatitscriticaltemperatureiscalleditscriticalpressure.

SOLIDSWhereasparticlesingaseshavethehighestdegreeofdisorder,thesolidstatehasthe most ordered system. Particles are fixed in rather definite positions andmaintain definite shapes. Because of their variation in packing, solids can bedivided into three categories: Crystalline solids have a three-dimensionalrepresentationmuch like abrickwall.Theyhave a regular structure, inwhichtheparticlespackinarepeatingpatternfromoneedgeofthesolidtotheother.Amorphous solids (literally, “solids without form”) have a random structure,with little ifany long-rangeorder.Polycrystalline solidsareanaggregateofalargenumberofsmallcrystalsorgrainsinwhichthestructureisregular,butthecrystalsorgrainsarearrangedinarandomfashion.Particles in solids do vibrate in position, however, and may even diffuse

throughthesolid.(Example:Goldclampedtoleadshowsdiffusionofsomegoldatoms into the lead over long periods of time.) Other solids do not showdiffusion because of strong ionic or covalent bonds in network solids.

(Examples:NaClanddiamond,respectively.)When heated at certain pressures, some solids vaporize directly without

passing through the liquid phase.This is called sublimation. Solids like solidcarbondioxideandsolidiodineexhibitthispropertybecauseofunusuallyhighvaporpressure.Thetemperatureatwhichatomicormolecularvibrationsofasolidbecomeso

greatthattheparticlesbreakfreefromfixedpositionsandbegintoslidefreelyover each other in a liquid state is called themelting point. The amount ofenergyrequiredatthemeltingpointtemperaturetocausethechangeofphasetooccur is called theheat of fusion. The amount of this energy depends on thenatureofthesolidandthetypeofbondspresent.

PHASEDIAGRAMSThesimplestwaytodiscussaphasediagramisbyanexample,suchasFigure25.Aphasediagramtiestogethertheeffectsoftemperatureandalsopressureon

the phase changes of a substance. In Figure 25 the lineBD is essentially thevapor-pressure curve for the liquid phase. Notice that at a pressure of 760millimetersofmercury(1atmosphere)thewaterwillboil(changetothevaporphase)at100°C(pointF).However, if thepressure is raised, theboilingpointtemperature increases; and, if the pressure is less than 760 millimeters, theboilingpointdecreasesalongtheBDcurvedowntopointB.

Figure25.PartialPhaseDiagramforWater(distortedsomewhattodistinguishthetriplepointfromthefreezingpoint)

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Know the significanceofeachgrayareaandboundaryline.

At0°Cthefreezingpointofwater is foundalongthe lineBCatpointE forpressure at 1 atmosphere or 760 millimeters. Again, this point is affected bypressurealongthelineBCsothat,ifpressureisdecreased,thefreezingpointisslightlyhigheruptopointBor0.01°C.PointBrepresentsthepointatwhichthesolid,liquid,andvaporphasesmay

all exist at equilibrium.This point is knownas the triplepoint. It is theonlytemperatureandpressureatwhichthreephasesofapuresubstancecanexistinequilibriumwithoneanotherinasystemcontainingonlythepuresubstance.

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The triple point is the onlytemperature and pressure at whichall three phases of a substance canexist.

WATERWater is so often involved in chemistry that it is important to have a rathercomplete understanding of this compound and its properties. Pure water hasbecome a matter of national concern. Although commercial methods ofpurificationwillnotbediscussedhere,theusuallaboratorymethodofobtainingpurewater,distillation,willbecovered.

PurificationofWaterThe process of distillation involves the evaporation and condensation of thewatermolecules.TheusualapparatusforthedistillationofanyliquidisshowninFigure26.Thismethodofpurificationwillremoveanysubstancethathasaboilingpoint

higherthanthatofwater.Itcannotremovedissolvedgasesorliquidsthatboiloffbefore water. These substances will be carried over into the condenser andsubsequentlyintothedistillate.

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In distillation, first boil and thencondense.

Figure26.Distillationofwater.

CompositionofWaterWatercanbeanalyzed,thatis,brokenintoitscomponents,byelectrolysis.Thisprocessshowsthatthecompositionofwaterbyvolumeis2partsofhydrogento1 part of oxygen. Water composition can also be arrived at by synthesis.Synthesisistheformationofacompoundbyunitingitscomponents.Watercanbe made by mixing hydrogen and oxygen in a eudiometer over mercury andpassinganignitingsparkthroughthemixture.Againtheratioofcombinationisfound to be 2 parts hydrogen: 1 part oxygen. In a steam-jacketed eudiometer,whichkeepsthewaterformedinthegasphase,2volumesofhydrogencombinewith1volumeofoxygentoform2volumesofsteam.Another interestingmethod is theDumas experiment pictured in Figure 27.

Dataobtainedshowthathydrogenandoxygencombinetoformwaterinaratioof1:8bymass.Thismeansthat1gramofhydrogencombineswith8gramsofoxygentoform9gramsofwater.

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Waterratiosofcombination:H2toO22vol:1volingaseousstate

1g:8gbymass

Figure27.SynthesisofWater

Somesampleproblemsinvolvingthecompositionofwaterareshownbelow.

TYPEPROBLEM(BYMASS):

An electric spark is passed through amixture of 12 grams ofhydrogen and 24 grams of oxygen in the eudiometer setupshown. Find the number of grams of water formed and thenumberofgramsofgasleftuncombined.

Sincewater forms ina ratioof1 :8bymass, touseup theoxygen(whichbyinspectionwillbethelimitingfactorsinceithasenoughhydrogenpresenttoreactcompletely)weneedonly3.0gramsofhydrogen.3.0gofhydrogen+24gofoxygen=27gofwaterThisleaves12g-3.0g=9.0gofhydrogenuncombined.

Amixtureof8millilitersofhydrogenand200millilitersofairisplacedinasteam-jacketedeudiometer,andasparkispassedthroughthemixture.Whatwillbe the totalvolumeofgases intheeudiometer?

Becausethisisacombinationbyvolume,8mLofhydrogenrequire4mLofoxygen.(RatioH2:O2byvolume=2:1.)

TYPEPROBLEM(BYVOLUME):

The 200mLof air is approximately 21%oxygen.Thiswill

more than supply theneededoxygenand leave196mLof theairuncombined.

The8mLofhydrogenand4mLofoxygenwillform8mLofsteam since the eudiometer is steam-jacketed and keeps thewaterformedinthegaseousstate.

(Ratiobyvolumeofhydrogen:oxygen:steam=2:1:2)TOTALVOLUME=196mLofair+8mLofsteam=204mL

HEAVYWATER.Asmallportionofwater iscalled“heavy”waterbecause itcontains an isotope of hydrogen, deuterium (symbol D), rather than ordinaryhydrogennuclei.Deuteriumhasanucleusofoneprotonandoneneutronratherthan just one proton. Another isotope of hydrogen is tritium. Its nucleus iscomposedoftwoneutronsandoneproton.Bothoftheseisotopeshavehaduseinthenuclearenergyfield.

HYDROGEN PEROXIDE. The prefix per- indicates that this compoundcontainsmore than the usual oxide. Its formula isH 2O2. It is awell-knownbleachingandoxidizingagent.Itselectron-dotformulaisshowninFigure28.

Figure28.HydrogenPeroxide

WaterCalorimetryProblemsA calorimeter is a container well insulated from outside sources of heat or

cold so thatmost of its heat is contained in the vessel. If a very hot object isplaced in a calorimeter containing some ice crystals, we can find the finaltemperature of themixturemathematically and check it experimentally. To dothis,however,certainbehaviorsmustbeunderstood.Icechangingtowaterandthen to steam does not represent a continuous and constant change oftemperatureastimeprogresses.Infact,thechartwouldlookasshowninFigure29.

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Water’sheatofvaporization=40.79kJ/mol

Figure29.ChangingIcetoSteam

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Water’sheatoffusion=6.01kJ/mol

Fromthisgraph,youseethatheatisbeingusedat0°Cand100°Ctochangethe state of water, but not its temperature. One gram of ice at 0°C needs 80caloriesor3.34×102joulestochangetowaterat0°C.Thisiscalleditsheatoffusion.Likewise,energyisbeingusedat100°Ctochangewatertosteam,nottochange the temperature. One gram ofwater at 100°C absorbs 540 calories or2.26×103joulesofheattochangeto1gramofsteamat100°C.Thisiscalleditsheatofvaporization.Thisenergyabsorbedattheplateausinthecurveisbeingused to break up the bonding forces between molecules by increasing thepotentialenergycontentof themoleculessothataspecificchangeofstatecanoccur.Theamountofheatenergyrequired tomeltonemoleofsolidat itsmelting

pointiscalleditsmolarheatoffusion.Ifthequantityoficemeltedisonemole(18grams),then,forice,itis6.01kJ/mole.Likewise,theamountofheatenergyrequired tovaporizeonemoleof liquid at its boilingpoint is called itsmolarheatofvaporization. If the quantity ofwater vaporized is onemole, then itsmolarheatofvaporizationis40.79kJ/mole.Thefollowingtwoproblemsaresamplesofcalorimetryproblems.Thefirstis

solvedbyusingtheSIunitsofjoules.Thesecondisdonebyusingcaloriesbutisfinallyconvertedtojoules.

EXAMPLE1:

Whatquantityoficeat273Kcanbemeltedby100.joulesofheat?Heattofuse(melt)asubstance=heatoffusionofthesubstance×massofthesubstance.Thisquantitycanbeexpressedbythefollowingformula,whereqdenotestheheatmeasurementmadeinacalorimeter:

q=m(mass)×C(heatoffusion)

Solvingform,weget

m=29.9×10−2gor0.299goficemelted.Becauseheatisabsorbedinmelting,thisisanendothermicaction.

EXAMPLE2:

Howmuchheatisneededtochange100.0gramsoficeat273Ktosteamat373K?Tomelt100.gramsoficeat273K:Use:m(mass)×C(heatoffusion)=q(quantityofheat)

Toheat100.gramsofwaterfrom273Kto373K:Use:m×ΔT×specificheat=q

Tovaporize100.gramsofwaterat100.°Ctosteamat100.°C:Use:m×heatofvaporization=q

Totalheat=33.44kJ+41.8kJ+225.72kJ=300.96kJ

Water’sReactionswithAnhydridesAnhydrides are certain oxides that react with water to form two classes ofcompounds—acidsandbases.Manymetaloxidesreactwithwatertoformbasessuchassodiumhydroxide,

potassium hydroxide, and calcium hydroxide. For this reason, they are calledbasicanhydridesorbasicoxides.Thecommonbasesarewatersolutionswhichcontainthehydroxyl(OH−)ion.Somecommonexamplesare:

Na2O+H2O→2NaOH,sodiumhydroxideCaO+H2O→Ca(OH)2,calciumhydroxide

Ingeneralthen:Metaloxide+H2O→Metalhydroxide

Inasimilarmanner,nonmetallicoxidesreactwithwatertoformanacidsuchas sulfuric acid, carbonic acid, or phosphoric acid. For this reason, they arereferred toasacidicoxidesoracidicanhydrides. (The termacidanhydride isnowusedtorefertospecificorganiccompounds.)Thecommonacidsarewatersolutionscontaininghydrogenions(H+).Somecommonexamplesare:CO2+H2O→H2CO3,carbonicacidSO3+H2O→H2SO4,sulfuricacidP2O5+3H2O→2H3PO4,phosphoricacid

Ingeneral,then:Nonmetallicoxide+H2O→Acid

POLARITYANDHYDROGENBONDINGWaterisdifferentfrommostliquidsinthatitreachesitsgreatestdensityat4°Cand then its volume begins to expand. By the time water freezes at 0°C, itsvolume has expanded by about 9 percent.Most other liquids contract as theycoolandchangestatetoasolidbecausetheirmoleculeshavelessenergy,movemore slowly, and are closer together.This abnormal behavior ofwater can beexplainedasfollows.X-raystudiesoficecrystalsshowthatH2Omoleculesarebound into largemolecules in which each oxygen atom is connected throughhydrogenbondstofourotheroxygenatomsasshowninFigure30.

Figure30.StudyofIceCrystal

Thisratherwideopenstructureaccountsforthelowdensityofice.Asheatisapplied and melting begins, this structure begins to collapse but not all thehydrogenbonds are broken.The collapsing increases the density of thewater,buttheremainingbondskeepthestructurefromcompletelycollapsing.Asheatisabsorbed, thekineticenergyof themoleculesbreaksmoreof thesebondsasthetemperaturerisesfrom0°to4°C.Atthesametimethisaddedkineticenergytendstodistributethemoleculesfartherapart.At4°Ctheseopposingforcesarein balance—thus the greatest density. Above 4°C the increasing molecularmotion again causes a decrease in density since it is the dominate force andoffsetsthebreakingofanymorehydrogenbonds.Thisbehaviorofwatercanbeexplainedbystudyingthewatermoleculeitself.

The water molecule is composed of two hydrogen atoms bonded by a polarcovalentbondtooneoxygenatom.

Because of the polar nature of the bond, themolecule exhibits the charges

shownintheabovedrawing.ItisthispolarchargethatcausesthepolarbondingdiscussedinChapter3asthehydrogenbond.Thisbondingisstrongerthantheusual molecular attraction called van der Waals forces or dipole-dipoleattractions.

SOLUBILITYWater is often referred to as “theuniversal solvent”becauseof thenumberofcommon substances that dissolve in water.When substances are dissolved inwatertotheextentthatnomorewilldissolveatthattemperature,thesolutionissaid to be saturated. The substance dissolved is called the solute and thedissolving medium is called a solvent. To give an accurate statement of asubstance’ssolubility,threeconditionsarementioned:theamountofsolute,theamount of solvent, and the temperature of the solution. Since the solubilityvaries for each substance and for different temperatures, a student must beacquaintedwiththeuseofsolubilitycurvessuchasthoseshowninFigure31.

Figure31.SolubilityCurvesofSomeCommonSalts

These curves show the number of grams of solute thatwill dissolve in 100grams(milliliters)ofwateroveratemperaturerangeof0°Cto100°C.Take,forexample,theverylowestcurveat0°C.ThiscurveshowsthenumberofgramsofKClO3thatwilldissolvein100gramsofwateroveratemperaturerangeof0°Cto 100°C. To find the solubility at any particular temperature, for example at

50°C,youfollowtheverticallineupfrom50°Cuntilitcrossesthecurve.Atthatpointyouplacearulerhorizontallyacrossthepageandtakethereadingontheverticalaxis.Thispointhappens tobeslightlybelow the20grammark,or18grams. This means that 18 grams of KClO3 will dissolve in 100 grams(milliliters)ofwaterat50°C.Asasolublesolute isadded towateratagiven temperature, thesolutewill

continue to go into solution until the water cannot dissolve anymore. This isshowngraphicallyinthefigurebelow.Itistheslopedportionofthegraph.Fromthatpointon,thesolutewillfalltothebottomanddoesnotdissolve,becauseanequilibrium has been established between molecules leaving and entering thesolidphase.Thisistheconditionwhenthelineonthegraphbecomeshorizontal.Thesolutionisholdingthemaximumamountofdissolvedsoluteinthisamountofwaterandat20°C.Thisisasaturatedsolution.Ifmorewaterisaddedtothesaturatedsolution, thenmoresodiumacetatewilldissolvein it.Asolutionthatcontains less solute than a saturated solution under the existing conditions isdescribedasanunsaturatedsolution.

TYPEPROBLEMUSINGTHESOLUBILITYCURVE:Asolutioncontains20gramsofKClO3 in200gramsofH2Oat80°C.How

manymoregramsofKClO3canbedissolvedtosaturatethesolutionat90°C?

Readingthegraphat90°anduptothegraphlineforKClO3,youfindthat100gramsofH2Ocandissolve48grams.Then200gramscanhold(2×48)gramsor96grams.Therefore96g−20g=76gKClO3canbeaddedtothesolution.

GeneralRulesofSolubilityAllnitrates,acetates,andchloratesaresoluble.

Allcommoncompoundsofsodium,potassium,andammoniumaresoluble.

Allchloridesaresolubleexceptthoseofsilver,mercury(I),andlead.(Leadchlorideisnoticeablysolubleinhotwater.)

Allsulfatesaresolubleexceptthoseoflead,barium,strontium,andcalcium.(Calciumsulfateisslightlysoluble.)

Thenormalcarbonates,phosphates,silicates,andsulfidesareinsolubleexceptthoseofsodium,potassium,andammonium.

Allhydroxidesareinsolubleexceptthoseofsodium,potassium,ammonium,calcium,barium,andstrontium.

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You should be familiar with thesegeneral rules of the solubility ofsolids.

Somegeneraltrendsofsolubilityareshowninthechartbelow.

TemperatureEffect PressureEffect

Solid Solubilityusuallyincreaseswithtemperatureincrease. Littleeffect

Gas Solubilityusuallydecreaseswithtemperatureincrease.

Solubilityvariesindirectproportiontothepressureappliedtoit:Henry’sLaw.

FactorsThatAffectRateofSolubility(HowFastTheyGoIntoSolution)

Thefollowingproceduresincreasetherateofsolubility

Pulverizing increasessurfaceexposedtosolvent.

Stirringbringsmoresolventthatisunsaturatedintocontactwithsolute.

Heating

increasesmolecularactionandgivesrisetomixingbyconvectioncurrents.(Thisheatingaffectsthesolubilityaswellasthe

rateofsolubility.)

SummaryofTypesofSolutesandRelationshipsofTypetoSolubilityGenerallyspeaking,solutesaremost likely todissolve insolventswithsimilarcharacteristics; that is, ionic and polar solutes dissolve in polar solvents, andnonpolarsolutesdissolveinnonpolarsolvents.Itshouldalsobementionedthatpolarmoleculesthatdonotionizeinaqueous

solution(e.g.,sugar,alcohol,glycerol)havemoleculesassoluteparticles;polarmolecules thatpartially ionize inaqueoussolution (e.g.,ammonia,aceticacid)have amixture ofmolecules and ions as solute particles; and polarmoleculesthat completely ionize in aqueous solution (e.g., hydrogen chloride, hydrogeniodide)haveionsassoluteparticles.

WATERSOLUTIONSTo make molecules or ions of another substance go into solution, watermoleculesmustovercometheforcesthatholdthesemoleculesorionstogether.Themechanismof theactualprocess iscomplex.Tomakesugarmoleculesgointosolution,thewatermoleculesclusteraroundthesugarmolecules,pullthemoff,anddisperse,formingthesolution.Foranioniccrystalsuchassalt,thewatermoleculesorientthemselvesaround

the ions (which are charged particles) and again must overcome the forcesholding the ions together. Since the water molecule is polar, this orientationaround the ion is an attraction of the polar ends of the water molecule. Forexample:

Oncesurrounded,theionisinsulatedtoanextentfromotherionsinsolution

becauseofthedipolepropertyofwater.Thewatermoleculesthatsurroundtheiondifferinnumberforvariousions,andthewholegroupiscalledahydratedion.In general, as stated in the preceding section, polar substances and ions

dissolve in polar solvents and nonpolar substances such as fats dissolve innonpolar solvents such as gasoline. The process of going into solution isexothermicifenergyisreleasedintheprocess,andendothermicifenergyfromthewater is used up to a greater extent than energy is released in freeing theparticle.Whentwoliquidsaremixedandtheydissolveineachother,theyaresaidto

be completelymiscible. If they separate and do not mix, they are said to beimmiscible.Twomoltenmetalsmay bemixed and allowed to cool. This gives a “solid

solution”calledanalloy.

CONTINUUMOFWATERMIXTURESFigure32showsthegeneralsizesoftheparticlesfoundinawatermixture.

Figure32.SizeofParticlesinWaterMixture

Thebasicdifferencebetweenacolloidandasuspensionisthediameteroftheparticles dispersed. All the boundaries marked in Figure 32 indicate only thegeneral ranges in which the distinctions between solutions, colloids, andsuspensionsareusuallymade.Thecharacteristicsofwatermixturesareasfollows:

Solutions Colloids Suspensions

………………..1nm…………………1,000nm………………………………….Clear;mayhavecolorParticlesdonotsettle.Particlespassthroughordinaryfilterpaper.

Cloudy;opaquecolorSettleonstandingDonotpassthroughordinaryfilterpaper

Particlespassthroughmembranes.

Donotpassthroughsemipermeablemembranessuchasanimalbladders,cellophane,andparchment,whichhaveverysmallpores*

Particlesarenotvisible. VisibleinultramicroscopeVisiblewithmicroscopeornakedeye

ShowBrownianmovement

NoBrownianmovement

* Separation of a solution from a colloidal dispersion through a semipermeable membrane is calleddialysis.

When a bright light is directed at right angles to the stage of anultramicroscope,theindividualreflectionsofcolloidalparticlescanbeobservedto be following a random zigzag path. This is explained as follows: Themolecules in the dispersingmedium are inmotion and continuously bumpinginto the colloidal particles, causing them to change direction in a randomfashion.Thismotion iscalledBrownianmovement after theScottishbotanistRobertBrown,whofirstobservedit.

EXPRESSIONSOFCONCENTRATIONThere are general terms and very specific terms used to express theconcentrationofasolution.Thegeneraltermsandtheirdefinitionsare:

Dilute =smallamountofsoluteisdispersedinthesolvent.Concentrated =largeamountofsoluteisdissolvedinthesolvent.

Saturated

=thesolutionisholdingallthesolutepossibleatthattemperature.Thisisnotastaticcondition;thatis,somesoluteparticlesareexchangingplaceswithsomeoftheundissolvedparticles,butthetotalsoluteinsolutionremainsthesame.Thisisanexampleofequilibrium.

Unsaturated =moresolutecangointosolutionatthattemperature.Thesolventhasfurthercapacitytoholdmoresolute.

Supersaturated

=sometimesasaturatedsolutionatahighertemperaturecanbecarefullycooledsothatthesolutedoesnotgetachancetocomeoutofsolution.Atalowertemperature,then,thesolutionwillbeholdingmoresoluteinsolutionthanitshouldforsaturationandissaidtobesupersaturated.Assoonasthesoluteparticlesarejarredora“seed”particleisaddedtothesolutiontoactasanucleus,theyrapidlycomeoutofsolutionsothatthesolutionrevertstothesaturatedstate.

It is interesting to note that thewords saturated andconcentrated areNOTsynonymous. Infact, it ispossible tohaveasaturateddilutesolutionwhenthesolute is only slightly soluble and a small amount of it makes the solutionsaturated,buttheconcentrationofthesolutionisstilldilute.

SpecificTermsofConcentrationThe more specific terms used to describe concentration are mathematicallycalculated.1.PERCENTAGECONCENTRATIONisbasedonthepercentofsolutein

thesolutionbymass.Thegeneralformulais:

EXAMPLE:

HowmanygramsofNaClareneededtoprepare200.gramsofa10%saltsolution?

10%of200.grams=20.0gramsofsalt

Youcouldalsosolvetheproblemusingtheaboveformulaandsolvingfortheunknownquantity.

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Knowhowtocalculatemolarity(M).

The next two expressions depend on the fact that, if the formulamass of asubstanceisexpressedingrams,itiscalledagram-formulamass(gfm),molar

mass,or1mole.Gram-molecularmasscanbeusedinplaceofgram-formulamasswhenthesubstanceisreallyofmolecularcomposition,andnotioniclikeNaClorNaOH.Thedefinitionsandexamplesare:

2. MOLARITY (abbreviated M) is defined as the number of moles of asubstancedissolvedin1literofsolution.

A1molarH2SO4solutionhas98.gramsofH2SO4(itsmolarmass)in1literofthesolution.

Thiscanbeexpressedasaformula:

Ifthemolarity(M)andthevolumeofasolutionareknown,themassofthesolutecanbedetermined.First,usetheaboveequationandsolveforthenumberofmolesofsolute.Then,multiplythisnumberbythemolarmass.

EXAMPLE: HowmanygramsofNaOHaredissolvedin200.millilitersofsolutionifitsconcentrationis1.50M?

Solvingfornumberofmolesgives:No.ofmolesofsolute=M×volumeinlitersofsolution

No.ofmolesofNaOH=1.50M×volumeinlitersofsolution

No.ofmolesofNaOH

ThemolarmassofNaOH=23+16+1.0=40gofNaOH

3.MOLALITY(abbreviatedm)isdefinedasthenumberofmolesofthesolutedissolvedin1,000gramsofsolvent.

EXAMPLE:A1molalsolutionofH2SO4has98gramsofH2SO4dissolvedin1,000.gramsofwater.This,youwillnotice,givesatotalvolumegreaterthan1liter,whereasthemolarsolutionhad98gramsin1literofsolution.

EXAMPLE:Supposethat0.25moleofsugarisdissolvedin500.gramsofwater.Whatisthemolalityofthissolution?

If0.25moleisin500.gramsofH2O,then0.50moleisin1,000gramsofH2O.Thus:

m=0.50

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Know how to determine the molefraction.

4. MOLE FRACTION is another way of indicating the concentration of acomponent in a solution. It is simply the number ofmoles of that componentdivided by the total moles of all the components. The mole fraction ofcomponentiiswrittenasXi.ForasolutionconsistingofnAmolesofcomponentA,nBmolesofcomponentB,nCmolesofcomponentC,andsoon,thenthemolefractionofcomponentAisgivenby:

Asanexample, ifamixture isobtainedbydissolving10molesofNaCl in90molesofwater,themolefractionofNaClinthatmixtureis10(molesofNaCl)dividedby(10+90)or100moles,givingananswerof0.1,themolefractionofNaCl.

DILUTIONIndilutionproblems,theexpressionofmolaritygivesthequantityofsolutepervolume of solution. The amount of solute dissolved in a given volume ofsolution is equal to theproductof the concentration times thevolume.Hence,0.5literof2Msolutioncontains

M×V=amountofsolute(inmoles)

Noticethatvolumeunitsmustbeidentical.

Ifyoudiluteasolutionwithwater,theamountornumberofmolesofsolutepresent remains the same, but the concentration changes. You can use theexpression:

BeforeAfterM1V1=M2V2

Thisexpressionisusefulinsolvingproblemsinvolvingdilution.

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Use this equation for dilutionproblems:M1V1=M2V21=solutionbefore2=solutionafter

EXAMPLE:Ifyouwishtomake1literofsolutionthatis6Minto3M

solution,howmuchwatermustbeadded?M1V1=M2V2

6M×1L=3M×xL

Solvingthisexpression:xL=2L.Thisisthetotalvolumeofthesolutionafterdilutionandmeansthat1literofwaterhadtobeaddedtotheoriginalvolumeof1litertogetatotalof2litersforthedilutesolutionvolume.

An important use of the molarity concept is in the solution of titrationproblems, which are covered in Chapter 11, along with pH expressions ofconcentrationforacids.

COLLIGATIVEPROPERTIESOFSOLUTIONSColligative properties are properties that depend primarily on the

concentrationofparticlesandnot the typeofparticle.There isusuallyadirectrelationshipbetweentheconcentrationofparticlesandtheeffectrecorded.Thevaporpressureofanaqueoussolutionisalwaysloweredbytheaddition

ofmore solute. From themolecular standpoint, it is easy to see that there arefewer molecules of water per unit volume in the liquid, and therefore fewermoleculesofwaterinthevaporphasearerequiredtomaintainequilibrium.Theconcentrationinthevapordropsandsodoesthepressurethatmoleculesexert.Thisisshowngraphicallybelow.Notice that the effectsof this change invaporpressure are registered in the

freezing point and the boiling point. The freezing point is lowered, and theboilingpoint is raised, indirectproportion to thenumberofparticlesofsolutepresent. For water solutions, the concentration expression that expresses thisrelationshipismolality(m),thatis,thenumberofmolesofsoluteperkilogramof solvent. Formolecules that do not dissociate, it has been found that a 1msolutionfreezesat−1.86°C(271.14K)andboilsat100.51°C(373.51K).A2msolutionwould then freezeat twice this lowering,or−3.72°C (269.28K), andboilattwicethe1molalincreaseof0.51°C,or101.02°C(374.02K).

VaporPressureVersusTemperatureforWaterandaSolution

Thechartbelowsummarizesthecolligativeeffectforaqueoussolutions.

EXAMPLE1:A1.50-gramsampleofureaisdissolvedin105.0gramsofwaterandproducesasolutionthatboilsat100.12°C.Fromthesedata,whatisthemolecularmassofurea?

Becausethispropertyisrelatedtothemolality,thenyoumustfindthenumberofgramsin1000gofwater.

x=14.28gin1,000gofwater

Theboilingpointchangeis0.12°C,andsinceeachmoleofparticlescausesa0.51°increase,then

Then14.28g=0.235moland

x=60.8g/molEXAMPLE2.Supposethattherearetwowatersolutions,oneofglucose

(molarmass=180.),theotherofsucrose(molarmass=342).Eachcontains50.0gramsofsolutein1,000.grams(1kg)ofwater.Whichhasthehigherboilingpoint?Thelowerfreezingpoint?Themolalityofeachofthesenonionizingsubstancesisfoundbydividingthenumberofgramsofsolutebythemolecularmass.

Thereforetheirrespectivemolalitiesare0.278mand0.146m.Sincethefreezingpointandboilingpointarecolligativeproperties,theeffectdependsonlyontheconcentration.Becausetheglucosehasahigherconcentration,itwillhaveahigherboilingpointandalowerfreezingpoint.Therespectiveboilingpointswouldbe:

Theloweringofthefreezingpointwouldbe:

Usingasolutethatisanionicsolidandthatcompletelyionizesinanaqueoussolution introduces consideration of the number of particles present in thesolution.Noticeintheprecedingchart thata1molalsolutionofNaClyieldsasolutionwith2molesofparticlesbecause:

NaCl(aq) Na+ Cl−

1moleofionic = 1moleof + 1moleofsodiumchloridesalt Na+ions Cl−ions

Thusa1molalsolutionofNaClhas2molesofionparticlesin1,000gramsofsolvent.Thecolligativepropertyof lowering thefreezingpointandraising theboilingpointdependsprimarilyontheconcentrationofparticlesandnotthetypeofparticles.In a 1 molal solution of NaCl, 1 mole of sodium chloride salt would be

dissolvedin1,000gramsofwatersothatatotalof2molesofionswerereleased—1moleofNa+ionsand1moleofCl−ions.Becausethisprovides2molesofparticles,itwillcausea2×−1.86°C(dropcausedby1mole)=−3.72°Cdropinthefreezingpoint.Likewise,itwillcausea2×0.51°C(risecausedby1mole)=+1.02°Criseintheboilingpointoraboilingpointof101.02°C.ThechartalsoshowsthatCaCl2releases3molesofparticlesfrom1moleof

CaCl2 dissolved in 1,000 grams of water. Note that its effect is to lower thefreezing point to 3 × −1.86°C or to −5.58°C. The boiling point rise is also 3timesthemolalriseof0.51°C,resultinginaboilingpointof101.53°C.This explains the use of salt on icy roads in the winter and the increased

effectiveness of calcium chloride per mole of solute. The use of glycols inantifreezesolutionsinautomobileradiatorsisalsobasedonthissameconcept.

CRYSTALLIZATIONManysubstancesformarepeatedpatternstructureastheycomeoutofsolution.Thestructureisboundedbyplanesurfacesthatmakedefiniteangleswitheach

othertoproduceageometricformcalledacrystal.Thesmallestportionofthecrystal lattice that is repeated throughout the crystal is called the unit cell.SamplesofunitcellsareshowninFigure33.The crystal structure can also be classified by its internal axis, as shown in

Figure34.

Figure33.KindsofUnitCells

Figure34.CrystalStructureClassifiedbyInternalAxis

Asubstancethatholdsadefiniteproportionofwaterinitscrystalstructureiscalled a hydrate. The formulas of hydrates show this water in the following

manner:CuSO4·5H2O;CaSO4·2H2O;andNa2CO3·10H2O.(The·isreadas“with.”)When these crystals are heated gently, thewater of hydration can beforcedoutofthecrystalandthestructurecollapsesintoananhydrous(withoutwater)powder.ThedehydrationofhydratedCuSO4 serves as a good examplesincethehydratedcrystalsaredeepbluebecauseofthecopperionspresentwithwatermolecules.When thiswater is removed, the structure crumbles into theanhydrous white powder. Some hydrated crystals, such as magnesium sulfate(Epsom salt), lose the water of hydration on exposure to air at ordinarytemperatures. They are said to be efflorescent. Other hydrates, such asmagnesiumchlorideandcalciumchloride,absorbwaterfromtheairandbecomewet.They are said to bedeliquescent orhydroscopic. This property explainswhycalciumchlorideisoftenusedasadryingagentinlaboratoryexperiments.

ChapterSummary

Thefollowingtermssummarizealltheconceptsandideasthatwereintroducedinthischapter.Youshouldbeabletoexplaintheirmeaningandhowyouwouldusetheminchemistry.Theyappearinboldfacetypeinthischaptertodrawyourattentiontothem.Theboldfacetypealsomakesiteasierforyoutolookthemupif you need to. You could also use the search or “Google” action on yourcomputer to get a quick and expanded explanation of these terms, laws, andformulas.

acidicanhydride endothermic molefraction efflorescent normalityalloy exothermic phaseequilibriumboilingpoint heatoffusion polarityBrownianmovement heatofvaporization saturatedcolligativeproperty “heavy”water soluteconcentrated hydrate solventcriticalpressure hydrogenbonds specificgravitycriticaltemperature LeChâtelier’sPrinciple sublimationcrystal meltingpoint surfacetension

deliquescent miscible/immiscible dilute molality viscositydynamicequilibrium molarity

InternetResourcesOnline content that reinforcesmajor concepts discussed in this chapter canbefound at the following Internet addresses if they are still available.Somemayhavebeenchangedordeleted.TheChemistryofWaterhttp://www.nsf.gov/news/special_reports/water/index_low.jspThis is a National Science Foundation site that offers a special report on thechemistryofwater.Ithasbeautifulartworktosupplementthetopics.PhaseDiagramshttp://www.chemguide.co.uk/physical/phaseeqia/phasediags.htmlThiswebsiteoffersclearexplanationsand interpretationsof the typesofphasediagramsthatafirst-yearchemistrystudentshouldbefamiliarwith.WhyDoSaltandSugarDissolveDifferently?http://www.inquiryinaction.org/chemistryreview/solids/Thissitegraphicallyanswersthisquestionaboutthedissolvingprocess.

PracticeExercises1.Distillationofwatercannotremove

(A)volatileliquidslikealcohol(B)dissolvedsalts(C)suspensions(D)precipitates

2.Theratioinwaterofhydrogentooxygenbymassis

(A)1:9(B)2:1

(C)1:2(D)1:8

3.Decomposingwaterbyanelectriccurrentwillgivearatioofhydrogentooxygenbyvolumeequalto

(A)1:9(B)2:1(C)1:2(D)1:8

4.If10.0gramsoficemeltsat0°C,thetotalquantityofheatabsorbedis

(A)10.0J(B)334J(C)3,340J(D)33,400J

5.Toheat10.0gramsofwaterfrom4°Cto14°Crequires

(A)10.0J(B)4.18J(C)418.J(D)4180.J

6.Theabnormallyhighboilingpointofwaterincomparisontosimilarcompoundsisdueprimarilyto

(A)vanderWaalsforces(B)polarcovalentbonding(C)dipoleinsulation(D)hydrogenbonding

7.Ametallicoxideplacedinwaterwouldmostlikelyyield

(A)anacid(B)abase(C)ametallicanhydride(D)abasicanhydride

8.Asolutioncanbeboth

(A)diluteandconcentrated(B)saturatedanddilute(C)saturatedandunsaturated(D)supersaturatedandsaturated

9.Thesolubilityofasolutemustindicate

(A)thetemperatureofthesolution(B)thequantityofsolute(C)thequantityofsolvent(D)alloftheabove.

10.Afoamisanexampleof

(A)agasdispersedinaliquid(B)aliquiddispersedinagas(C)asoliddispersedinaliquid(D)aliquiddispersedinaliquid

11.Whenanothercrystalwasaddedtoawatersolutionofthesamesubstance,thecrystalseemedtoremainunchanged.Itsparticleswere

(A)goingintoanunsaturatedsolution(B)exchangingplaceswithothersinthesolution(C)causingthesolutiontobecomesupersaturated(D)notgoingintosolutioninthisstaticcondition

12.A10.%solutionofNaClmeansthatin100.gramsofsolutionthereis

(A)5.85gNaCl(B)58.5gNaCl(C)10.gNaCl(D)94gofH2O

13.ThemolarmassofAlCl3is

(A)62.5g/mol(B)67.9g/mol(C)106.5g/mol(D)133.5g/mol

14.Themolarityofasolutionmadebyplacing98gramsofH2SO4insufficientwatertomake500.millilitersofsolutionis

(A)0.5(B)1(C)2(D)3

15.If684gramsofsucrose(molecularmass=342g/mol)isdissolvedin2,000gramsofwater(essentially2L),whatwillbethefreezingpointofthissolution?

(A)−.51°C(B)−1.86°C(C)−3.72°C(D)−6.58°C

ThefollowingquestionsareintheformatthatisusedontheSATSubjectTestinChemistry.Ifyouarenotfamiliarwiththesetypesofquestions,studybeforedoingtheremainderofthereviewquestions.

Directions: Each of the following sets of lettered choices refers to thenumberedquestionsimmediatelybelowit.Foreachnumbereditem,choosetheoneletteredchoicethatfits itbest.Everychoiceinasetmaybeusedonce,morethanonce,ornotatall.

Questions16–18refertothefollowinggraphs:

16.Whichofthegraphsrepresentsthesolubilitycurveofasubstancethathasnochangeinitssolubilityasthetemperatureincreases?

17.Whichofthegraphsrepresentstheamountofasoluteinasolutionasthesoluteisaddedevenafterthesaturationpointisreachedandnomorecangointosolution?

18.Whichofthegraphsrepresentsthetemperatureofasampleoficeovertimeasitisheatedatanevenratefrombelowitsfreezingpointtoatemperaturewhereitisintheliquidstateabovethefreezingpoint?

Questions19–20

(A)1molar(B)1molal(C).5molar(D).5molal(E)25molar

19.TheconcentrationofasolutionofCa(OH)2when74gramsarecompletelydissolvedinacontainerholding2litersofwater?

20.Theconcentrationofasolutionofsucrose,C12H22O11,when684gramsarecompletelydissolvedin2,000gramsofwater?

AnswersandExplanations1.(A)Volatileliquidscannotberemovedbydistillationbecausetheywouldcomeoverwiththesteaminthisprocess.

2.(D)Inthemolarmassofwater,thereare2hydrogen=2gand1oxygen=16g.SotheH/Oratiobymassis2g/16gor1/8.

3.(B)Inthebalancedreaction,2H2O→2H2(g)+O2(g),2volumesofhydrogenarereleasedto1volumeofoxygen,sotheratiois2:1.

4.(C)Ittakes334Jtomelt1g(heatoffusionfor1gram)so10g×334J/g=3,340Jtomelttheice.

5.(C)m(mass)×ΔT(changeoftemperature)×specificheat=q(quantityofheat).So,10.0g×(14°-4°=10°)×4.18J/°/g=418.J.

6.(D)Becausehydrogenbondingissostronginwater,ittakesmoreheatenergytoreachitsboilingpoint.

7.(B)Metaloxidesareacidanhydrides,becausetheyreactwithwatertoformacids.Example:CaO+H2O→Ca(OH)2

8.(B)Saturatedmeansthatthesolutionisholdingallthesoluteitcanatthattemperature.Dilutemeansthatthereisasmallamountofsoluteinsolutioncomparedwiththeamountofsolvent.Soasubstancethatisonlyslightlysolublecanformasaturateddilutesolution.

9.(D)Solubilityofasolutemustgivetheamountofsolutedissolvedinagivenamountofsolventataparticulartemperature.

10.(A)Afoamisanexampleofacolloidaldispersionofagasinaliquid.

11.(B)Thissituationdescribesasaturatedsolutionwhereanequilibriumexistsbetweentheundissolvedsoluteandthesoluteparticlesinsolution.

12.(C)A10.%solutioncontains10.gofsolute/100.gofsolutionbecausethepercentageisbymass/100gofsolution.

13.(D)ThemolarmassisequaltothetotalofAl=27+3Cl=106.5foratotalof133.5g/mol.

14.(C)98gH2SO4=1molH2SO4So,ifthereare500mL(whichis0.5L)then1molin0.5Lwouldbeequivalentto2molin1Lora2molarsolution.

15.(B)684gofsucrose= =2molofsucrose

So =1molalsolution(1m)

Thefreezingpointisloweredto–1.86°C

16.(A)Thegraphofthesolubilityofasubstancethathasnochangeinitssolubilityasthetemperatureisincreasedwouldbeastraightline,asshowninA.

17.(C)ThegraphthatshowstheamountofsoluteinsolutionasitisaddedupthroughitssaturationpointisC.Thepointatwhichsaturationoccursiswherethelineflattensouttoahorizontalstraightline.

18.(D)GraphDshowstheicegettingwarmeruntilitstartstomelt.Thisiswherethetemperaturestaysthesameuntilitisallmelted.Theheatbeingaddedisbeingusedforthechangeinstatefromasolidtoaliquidandthelinestayshorizontal,indicatingnochangeintemperatureduringthistime.Thelinethenstartstoascendasliquidwaterisabsorbingtheheatandincreasingintemperature.

19.(C)ThemolarmassofCa(OH)2isCa=40,2O=32,and2H=2,which,addedtogetherequals74g/mol.Ifthisisdissolvedtomakea2Lsolution,thereisonly.5molin1L.Sothemolarity(M),themolesofsolutein1L=.5M

20.(B)ThemolarmassofC12H22O11is12C=144,22H=22,and11O=176,whichaddedtogetherequals342g/mol.Because684gisgiven,then684gdividedby342g/mol=2molofsucrose.Ifthisisdissolvedin2,000gofwater,itgives1mol/1,000gofwaterora1molalsolution.

CHAPTER8

ChemicalReactionsandThermochemistry

TheseskillsareusuallytestedontheSATSubjectTestinChemistry.Youshouldbeableto…•Identifythedrivingforceforthesefourmajortypesofchemicalreactions,andwritebalancedequationsforeach:combination(orsynthesis),decomposition(oranalysis),singlereplacement,anddoublereplacement.

•Explainhydrolysisusingabalancedequation.•Identifyandexplaingraphicallyenthalpychangesinexothermicandendothermicreactions.

•UseHess’sLawtoshowtheadditivityofheatsofreactions.•Calculateenthalpyfrombondenergies.This chapter will review and strengthen these skills. Be sure to do thePracticeExercisesattheendofthechapter.

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Know the four types of chemicalreactions:1.Combinationorsynthesis2.Decompositionoranalysis3.Singlereplacement4.Doublereplacement

Themanykindsof reactionsyoumayencountercanbeplaced into fourbasiccategories: combination, decomposition, single replacement, and doublereplacement. The first type, combination, can also be called synthesis. Thismeans the formation of a compound from the union of its elements. Some

examplesofthistypeare:Zn(s)+S(s)→ZnS(s)

2H2(g)+O2(g)→2H2O(g)C(s)+O2(g)→CO2(g)

The second type of reaction, decomposition, can also be referred to asanalysis.Thismeansthebreakdownofacompoundtoreleaseitscomponentsasindividualelementsorothercompounds.Someexamplesofthistypeare:

2H2O( )→2H2(g)+O2(g)(electrolysisofwater)C12H22O11(s)→12C(s)+11H2O( )

2HgO(s)→2Hg(s)+O2(g)

The third type of reaction is called single replacement or singledisplacement.Thistypecanbestbeshownbyexamplesinwhichonesubstanceisdisplacinganother.Someexamplesare:

Fe(s)+CuSO4(aq)→FeSO4(aq)+Cu(s)Zn(s)+H2SO4(aq)→ZnSO4(aq)+H2(g)

Cu(s)+2AgNO3(aq)→Cu(NO3)2(aq)+2Ag(s)

The last type of reaction is called double replacement or doubledisplacement because there is an actual exchange of “partners” to form newcompounds.Someexamplesare:

PREDICTINGREACTIONSOne of the most important topics of chemistry deals with the reasons whyreactionstakeplace.Takingeachoftheabovetypesofreactions,letusseehowapredictioncanbemadeconcerninghowthereactiongetsthedrivingforcetomakeitoccur.

1.Combination(AlsoKnownasSynthesis)Thebestsourceofinformationtopredictachemicalcombinationistheheatof

formation table. A heat of formation table gives the number of kilojoulesevolved or absorbed when a mole (gram-formula mass) of the compound inquestion is formedby the direct union of its elements. In this book a positivenumber indicates that heat is absorbed and a negative number that heat isevolved. It makes some difference whether the compounds formed are in thesolid,liquid,orgaseousstate.Unlessotherwiseindicated(g=gas, = liquid),the compounds are in the solid state. The values given are in kilojoules, 4.18joulesistheamountofheatneededtoraisethetemperatureof1gramofwater1degree on the Kelvin scale. The symbol ΔH is used to indicate the heat offormation.

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–ΔH=exothermicreaction+ΔH=endothermicreaction

If the heat of formation is a large number preceded by a minus sign, thecombinationislikelytooccurspontaneouslyandthereactionisexothermic.If,ontheotherhand,thenumberissmallandnegativeorispositive,heatwillbeneededtogetthereactiontoproceedatanynoticeablerate.Someexamplesare:

EXAMPLE1:Zn(s)+S(s)→ZnS(s)+202.7kJΔH=−202.7kJ

Thismeansthat1moleofzinc(65grams)reactswith1moleofsulfur(32grams)toform1moleofzincsulfide(97grams)andreleases202.7kilojoulesofheat.

EXAMPLE2:Mg(s)+ O2(g)→MgO(s)+601.6kJΔH=−601.6kJ/mol

indicatesthattheformationof1moleofmagnesiumoxiderequires1moleofmagnesiumand moleofoxygenwiththereleaseof601.6kJofheat.Noticetheuseofthefractionalcoefficientforoxygen.Iftheequationhadbeenwrittenwiththeusualwhole-numbercoefficients,2molesofmagnesiumoxidewouldhavebeenreleased.

Since,bydefinition,theheatofformationisgivenfortheformationof1mole,thislatterthermalequationshows2×(−601.6)kJreleased.

EXAMPLE3:H2(g)+ O2(g)→H2O( )+285.8kJΔH=−285.8kJ

Incombustionreactionstheheatevolvedwhen1moleofasubstanceiscompletelyoxidizediscalledtheheatofcombustionofthesubstance,so,inthisequation:

ΔHistheheatofcombustionofcarbon.Becausetheenergyofasystemisconservedduringchemicalactivity,thesameequationcouldbearrivedatbyaddingthefollowingequations:

2.Decomposition(AlsoKnownasAnalysis)Thepredictionofdecompositionreactionsusesthesamesourceofinformation,theheatofformationtable.Iftheheatofformationisahighexothermic(ΔHisnegative) value, the compoundwill be difficult to decompose since this samequantityofenergymustbereturnedtothecompound.Alowheatofformationindicates decomposition would not be difficult, such as the decomposition ofmercuricoxidewithΔH=−90.8kJ/mole:

2HgO(s)→2Hg(s)+O2(g)(Priestley’smethodofpreparation)

Ahighpositiveheatof formation indicatesextreme instabilityofacompound,whichcanexplosivelydecompose.

3.SingleReplacementA prediction of the feasibility of this type of reaction can be based on acomparison of the heat of formation of the original compound and that of thecompound to be formed.For example, in a reaction of zincwith hydrochloric

acid,the2molesofHClhaveΔH=2×−92.3kJ.

EXAMPLE1:

andthezincchloridehasΔH=−415.5kJ.Thiscomparisonleavesanexcessof230.9kJofheatgivenoff,sothereactionwouldoccur.

EXAMPLE2:

Inthisnextexample,−928.4−(−771.4)=−157.0kJ,whichistheexcesstobegivenoffasthereactionoccurs:

Anothersimplewayofpredictingsinglereplacementreactionsistochecktherelativepositionsofthetwoelementsintheactivityseriesbelow.Iftheelementthatistoreplacetheotherinthecompoundishigheronthechart, thereactionwilloccur.Ifitisbelow,therewillbenoreaction.Somesimpleexamplesofthisarethefollowingreactions.In predicting the replacement of hydrogen by zinc in hydrochloric acid,

reference to the activity series shows that zinc will replace hydrogen. Thisreactionwouldoccur:

Infact,mostmetals in theactivityserieswouldreplacehydrogeninanacidsolution.Ifametalsuchascopperwerechosen,noreactionwouldoccur.

Cu(s)+HCl(aq)→noreactionThe determination of these replacements using a quantitative method is

coveredinChapter12.

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Knowhow touse this activity seriestopredictreactions.

4.DoubleReplacementFordoublereplacementreactionstogotocompletion,thatis,proceeduntilthesupplyofoneofthereactantsisexhausted,oneofthefollowingconditionsmustbepresent:(1)aninsolubleprecipitateisformed,(2)anonionizingsubstanceisformed,or(3)agaseousproductisgivenoff.

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Know these three conditions forgoingtocompletion.

1.Topredicttheformationofaninsolubleprecipitate,youshouldhavesomeknowledgeofthesolubilitiesofcompounds.Table9givessomegeneralsolubilityrules.

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Knowthegeneralsolubilityrules.

(Atableofsolubilitiescouldalsobeusedasreference.)

Anexampleofthistypeofreactionisgiveninitscompleteionicform.

Thesilverionscombinewiththechlorideionstoformaninsolubleprecipitate,silverchloride.Ifthereactionhadbeenlikethis:

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Notice that the ions “switch”partners.

merelyamixtureoftheionswouldhavebeenshowninthefinalsolution.

2.Anotherreasonforareactionofthistypetogotocompletionistheformationofanonionizingproductsuchaswater.Thisweakelectrolytekeepsitscomponentionsinmolecularformandthuseliminatesthepossibilityofreversingthereaction.Allneutralizationreactionsareofthistype.

(H++Cl−)+(Na++OH−)→H2O(l)+Na++Cl−

Thisexampleshowstheionsofthereactants,hydrochloricacidandsodiumhydroxide,andthenonelectrolyteproductwaterwithsodiumandchlorideionsinsolution.Sincethewaterdoesnotionizetoanyextent,thereversereactioncannotoccur.

Thethirdreasonfordoubledisplacementtooccuristheevolutionofagaseousproduct.Anexampleofthisiscalciumcarbonatereactingwithhydrochloricacid:

CaCO3(s)+2HCl(aq)→CaCl2(aq)+H2O(l)+CO2(g)3.Anotherexampleofacompoundthatevolvesagasinsodiumsulfitewithanacidis:

Na2SO3(aq)+2HCl(aq)→2NaCl(aq)+H2O(l)+SO2(g)Ingeneral, acidswith carbonatesor sulfites aregoodexamplesof this typeof

equation.

HydrolysisReactionsHydrolysis reactions are the opposite of neutralization reactions. In hydrolysisthe salt and water react to form an acid and a base. For example, if sodiumchlorideisplacedinsolution,thisreactionoccurstosomedegree:

(Na++Cl−)+H2O(l)→(Na++OH−)+(H++Cl−)

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Saltinteractswithwater.

Inthishydrolysisreactionthesamenumberofhydrogenionsandofhydroxideions is released so that the solution is neutral. This occurs because sodiumhydroxide is a strong base and hydrochloric acid is a strong acid. (There arechartsofrelativeacidandbasestrengthstouseasreferences.)Becausetheyareboth classified as strong, sodium hydroxide and hydrochloric acid essentiallyexistasionsinsolutions.Therefore,theNaClsolutionhasanexcessofneitherhydrogennorhydroxideions,anditwill testneutral.Thus, thesaltofastrongacid and a strong base forms a neutral solution when dissolved in water.However,ifNa2CO3isdissolved,wehave:

(2Na++CO32−)+2H2O( )→(2Na++2OH−)+H2CO3

TheH2CO3iswrittenasasingleentitybecauseitisaslightlyionizedacid,or,inotherwords,aweakacid.Sincethehydroxideionsarefreeinthesolution,thesolutionisbasic.Noticethathereitwasthesaltofastrongbaseandaweakacidthatformedabasicsolution.Thisgeneralizationistrueforthistypeofsalt.If we use ZnCl2, which is the salt of a strong acid and a weak base, the

reactionwillbe:(Zn2++2Cl−)+H2O(l)→(2H++2Cl−)+Zn(OH)2

Inthiscasethehydroxideionsareheldintheweaklyionizingcompoundwhilethehydrogenionsarefreetomakethesolutionacidic.Ingeneral,then,thesaltofastrongacidandaweakbaseformsanacidsolutionbyhydrolysis.Thefourthpossibilityisthatofasaltofaweakacidandweakbasedissolving

inwater.Anexamplewouldbeammoniumcarbonate,(NH4)2CO3,whichisthe

saltofaweakbaseandaweakacid.Thehydrolysisreactionwouldbe:(NH4)2CO3+2H2O(l)→2NH4OH+H2CO3

Both theammoniumhydroxide,NH4OH,and thecarbonicacid,H2CO3, arewrittenasnonionizedcompoundsbecausetheyareclassifiedasaweakbaseandaweakacid,respectively.Therefore,asaltofaweakacidandaweakbaseformsaneutralsolutionsinceneitherhydrogenionnorhydroxideionwillbepresentinexcess.

EntropyIn many of the preceding predictions of reactions, we used the concept thatreactionswilloccurwhentheyresultinthelowestpossibleenergystate.There is, however, another driving force to reactions that is related to their

stateofdisorderorof randomness.This stateofdisorder is calledentropy. Areaction is also driven, then, by a need for a greater degree of disorder. Anexample is the intermixing of gases in two connected flasks when a valve isopened to allow the two previously isolated gases to travel between the twoflasks.Because temperature remains constant throughout the process, the totalheatcontentcannothavechangedtoalowerenergylevel,andyetthegaseswillbecome evenly distributed in the two flasks. The system has thus reached ahigherdegreeofdisorderorentropy.

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Entropy is ameasure of the degreeofdisorder.

THERMOCHEMISTRYIn general, all chemical reactions either liberate or absorb heat. The origin ofchemical energy lies in the position and motion of atoms, molecules, andsubatomicparticles.Thetotalenergypossessedbyamoleculeisthesumofalltheformsofpotentialandkineticenergyassociatedwithit.Theenergychangesinareactionaredue,toalargeextent,tothechangesin

potentialenergythataccompanythebreakingofchemicalbondsinreactantstoformnewbondsinproducts.

Themoleculemayalsohaverotational,vibrational,andtranslationalenergy,alongwithsomenuclearenergysources.All thesemakeupthetotalenergyofmolecules. In beginning chemistry, the greatest concern in reactions is theelectronicenergyinvolvedinthemakingandbreakingofchemicalbonds.Becauseitisvirtuallyimpossibletomeasurethetotalenergyofmolecules,the

energy change is usually the experimental data thatwe dealwith in reactions.This change in quantity of energy is known as the change in enthalpy (heatcontent)ofthechemicalsystemandissymbolizedbyΔH.

CHANGESINENTHALPYChanges in enthalpy for exothermic and endothermic reactions can be showngraphically,asintheexamplesbelow.

NoticethattheΔH foranendothermicreaction ispositive,while that foranexothermicreactionisnegative.Itshouldbenotedalsothatchangesinenthalpyarealwaysindependentofthepathtakentochangeasystemfromtheinitialstatetothefinalstate.

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This paragraph gives the definitionofthemolarheatofformation.

Because the quantity of heat absorbed or liberated during a reaction varies

withthetemperature,scientistshaveadopted25°Cand1atmospherepressureasthestandardstateconditionfor reportingheatdata.AsuperscriptzeroonΔH(i.e., ΔH0) indicates that the corresponding process was carried out understandard conditions. The standard enthalpy of formation (ΔH0

f) of acompoundisdefinedasthechangeinenthalpythataccompaniestheformationof1moleofacompoundfromitselementswithallsubstancesintheirstandardstatesat25°C.Thisvalueiscalledthemolarheatofformation.Tocalculatetheenthalpyofareaction,itisnecessarytowriteanequationfor

thereaction.Thestandardenthalpychange,ΔH, foragivenreactionisusuallyexpressed in kilocalories and depends on how the equation is written. Forexample,thefollowingequationsexpressthereactionofhydrogenwithoxygenintwoways:

Experimentally, ΔH0f for the formation of 1 mole of H2O(g) is −241.8 kJ.

Since the second equation represents the formation of 2moles ofH2O(g), thequantity is twice −241.8, or −483.6 kJ. It is assumed that the initial and finalstatesaremeasuredat25°Cand1atmosphere,althoughthereactionoccursatahighertemperature.

PROBLEM:Howmuchheatisliberatedwhen40.0gramsofH2(g)reactswithexcessO(g)?Thereactionequationis:

Thisrepresents1molor2gofH(g)forming1molofH2O(g):

Sinceeachmolegivesoff−241.8kJ,then

Noticethatthephysicalstateofeachparticipantmustbegivensincethephasechanges involveenergychanges.Combustion reactionsproduceaconsiderable

amountof energy in the formof light andheatwhena substance is combinedwith oxygen. The heat released by the complete combustion of 1 mole of asubstance is called the heat of combustion of that substance. Heat ofcombustion is defined in terms of 1 mole of reactant, whereas the heat offormation isdefined in termsof1moleofproduct.All substancesare in theirstandardstate.Thegeneralenthalpynotation,ΔH, applies toheatsof reaction,buttheadditionofasubscriptc,ΔHc,specificallyindicatesheatofcombustion.

ADDITIVITYOFREACTIONHEATSANDHESS’SLAWChemicalequationsandΔH0valuesmaybemanipulatedalgebraically.FindingtheΔHfortheformationofvaporfromliquidwatershowshowthiscanbedone.

SincewewanttheequationforH2O(l)→H2O(g),wecanreversethesecondequation.ThischangesthesignofΔH.

Simplificationgivesthenetequation:

TIP

KnowhowtouseHess’sLaw.

TheprincipleunderlyingtheprecedingcalculationsisknownasHess’sLawofHeatSummation.Thisprinciplestatesthat,whenareactioncanbeexpressedas thealgebraicsumof twoormoreotherreactions, theheatof thereactionisthealgebraic sumof theheatsof these reactions.This isbasedupon theFirstLawofThermodynamics,which,simplystated,saysthatthetotalenergyoftheuniverseisconstantandcannotbecreatedordestroyed.These laws allow calculations of ΔH’s that cannot be easily determined

experimentally.AnexampleisthedeterminationoftheΔHofCOfromtheΔH0f

ofCO2.

Thecalculationfortheaboveexampleisshownbelow.

Theequationwantedis

Togetthis,wereversethesecondequationandaddittothefirst:

Additionyields

Thisrelationshipcanalsobeshownschematicallyasfollows:

Some commonly used standard heats of formation (enthalpy), designated asΔH0

f,arelistedinTable intheTablesforReferencesection.An alternative (and easier)methodof calculating enthalpies is basedon the

conceptthatΔH0reaction

isequaltothedifferencebetweenthetotalenthalpyofthereactantsandthatoftheproducts.Thiscanbeexpressedasfollows:

PROBLEM:CalculateΔH0reaction

forthedecompositionofsodiumchlorate.

ChapterSummaryThefollowingtermssummarizealltheconceptsandideasthatwereintroducedinthischapter.Youshouldbeabletoexplaintheirmeaningandhowyouwouldusetheminchemistry.Theyappearinboldfacetypeinthischaptertodrawyourattentiontothem.Theboldfacetypealsomakesiteasierforyoutolookthemupif you need to. You could also use the search or “Google” action on yourcomputer to get a quick and expanded explanation of these terms, laws, andformulas.

combinationreaction heatofformationdecompositionreaction hydrolysisreactiondoublereplacementreaction molarheatofformationenthalpy singlereplacementreactionentropy standardenthalpyofformationheatofcombustion

FirstLawofThermodynamicsHess’sLawofHeatSummation

InternetResourcesOnline content that reinforcesmajor concepts discussed in this chapter canbefound at the following Internet addresses if they are still available.Somemayhavebeenchangedordeleted.ClassificationofChemicalReactionshttp://boyles.sdsmt.edu/subhead/types_of_reactions.htmThissitegivesaverygoodoverviewofvarious typesofchemical reactionsaswellasvideoaccesstotheactualreactionoccurring.Hess’sLawhttp://chemistry2.csudh.edu/lecture_help/Hesslaw.htmlThisWebpagegivesyouachancetosolveproblemsrelatedtoHess’sLawandreceiveinstantfeedbackabouttheaccuracyofyourcalculations.

PracticeExercises1.Asynthesisreactionwilloccurspontaneouslyaftertheactivationenergyisprovidediftheheatofformationoftheproductis

(A)largeandnegative(B)smallandnegative(C)largeandpositive(D)smallandpositive

2.ThereactionofaluminumwithdiluteH2SO4canbeclassifiedas

(A)synthesis(B)decomposition(C)singlereplacement(D)doublereplacement

3.Forametalatomtoreplaceanotherkindofmetallicioninasolution,themetalatommustbe

(A)agoodoxidizingagent(B)higherintheactivityseriesthanthemetalinsolution(C)lowerintheelectromotivechartthanthemetalinsolution(D)equalinactivitytothemetalinsolution

4.Onereasonforadoubledisplacementreactiontogotocompletionisthat

(A)aproductissoluble(B)aproductisgivenoffasagas(C)theproductscanreactwitheachother(D)theproductsaremiscible

5.Hydrolysiswillgiveanacidreactionwhenwhichoftheseisplacedinsolutionwithwater?

(A)Na2SO4

(B)K2SO4

(C)NaNO3

(D)Cu(NO3)2

6.Asaltderivedfromastrongbaseandaweakacidwillundergohydrolysisandgiveasolutionthatwillbe

(A)basic(B)acid(C)neutral(D)volatile

7.Enthalpyisanexpressionforthe

(A)heatcontent(B)energystate(C)reactionrate(D)activationenergy

8.TheΔH0fofareactionisrecordedfor

(A)273K(B)298K(C)373K(D)473K

9.Thepropertyofbeingabletoaddenthalpiesisbasedonthe

(A)LawofConservationofHeat(B)FirstLawofThermodynamics(C)LawofConstants(D)Einsteinequation,E=mc2

10.AΔHreaction

of–100kJ/moleindicatesthereactionis

(A)endothermic(B)unstable(C)inneedofacatalyst(D)exothermic

Directions:

Before attempting to answer the following questions (11–15), you may

wanttoreviewthedirectionsforthistypeofquestion.

Everyquestionbelowcontainstwostatements,IinthelefthandcolumnandIIintheright-handcolumn.Foreachquestion,decideifstatementIistrueor false and whether statement II is true or false, and fill in thecorrespondingTorFovals in theanswerspaces.*Fill inovalCEonly ifstatementIIisacorrectexplanationofstatementI.

I II

11.Iftheheatofformationofacompoundisalargenumberprecededbyaminussign,thereactionisexothermic

BECAUSE

the First Law ofThermodynamics states that anegative heat of formation isassociated with an exothermicreaction.

12.TheburningofcarbonwithexcessO2toformCO2willgotocompletion

BECAUSE

when a reaction results in thereleaseofagasthatisallowedtoescape, the reaction will go tocompletion.

I II13.Theheatofformationofa

compoundcanbecalculatedbyalgebraicallyaddingtwoormorethermalreactionequations

BECAUSE

Hess’s Law states that a heat ofreactioncanbearrivedatby thealgebraic summation of two ormoreotherthermalreactions.

14.Entropycanbedescribedasthestateofdisorderofasystem

BECAUSEwhenhighamountsofenergyarereleased from a reaction, thereactionissaidtobeexothermic.

15.ThereactioninwhichHgOis in a decomposition reaction, theoriginal compound is broken

heatedtoreleaseO2iscalledadecomposition

BECAUSE apart into equal numbers ofatoms.

AnswersandExplanations1.(A)Alargenegativeheatofformationindicatesthatthereactionwillgiveoffalargeamountofenergyandwillself-perpetuateaftergettingtheactivationenergynecessaryforittostart,likeburningpaper.

2.(C)Becausethealuminumreplacesthehydrogentoformaluminumsulfate,thisisclassifiedasasingle-replacementreaction.

3.(B)Forametaltoreplaceanothermetallicioninasolution,itmustbehigherintheactivityseriesofelementsthanthemetalinsolution.

4.(B)Foradoubledisplacementtogotocompletion,aproductorproductsmusteitherdepositasaprecipitateorleavethereactionasagas.

5.(D)TheonlysaltthathydrolyzestoastrongacidandaweakbaseisCu(NO3)2.Thiswouldgiveanacidsolution.Alltheothersaresaltsofstrongacidsandstrongbases,sotheywouldhydrolyzetoarelativelyneutralsolution.

6.(A)Saltsofstrongbasesandweakacidsreactwithwatertogiveabasicsolution.AnexamplewouldbeNa2CO3,becauseithydrolyzesintoNaOH,astrongbase,andH2CO3,aweakacid.

7.(A)Enthalpyisdefinedastheheatcontentofasystem.

8.(B)TheΔH0withthesuperscriptzeroindicatesthattheprocesswascarriedoutunderstandardconditions,whichare298Kand1atmospherepressure.

9.(B)ThepropertyofbeingabletoaddenthalpiescomesfromHess’sLawofHeatSummationandisbasedontheFirstLawofThermodynamics,whichsimplysaysthatthetotalenergyoftheuniverseisconstantandcannotbecreatedordestroyed.

10.(D)Becausetheheatofthereactionisnegative,itindicatesthatenergy(heat)isgivenoffwhenthisreactionoccurs.Itisthereforeanexothermicreaction.

11.(T,F)Whileitistruethatanegativeheatofformationisassociatedwithanexothermicreaction,theFirstLawofThermodynamicsstatesthatthetotalenergyoftheuniverseisconstantandcannotbeeasilycreatednordestroyed.Itisaconventionofchemistrythatenergygivenofffromacombinationreactionisgivenanegativevalue.

12.(T,T,CE)Whenacombinationreactionresultsinagasthatisallowedtobereleased,aprecipitatethatdropstothebottomofthecontainer,oranonionizingproduct,thereactionwillgotocompletion.

13.(T,T,CE)BothstatementsaretrueandHess’sLawisthebasisforarrivingataheatofreactionbyalgebraicallyaddingtwoormorethermalequations.

14.(T,T)Bothstatementsaretrue,buttheseconddoesnotexplainthefirst,andthereisnocauseandeffectrelationship.Entropyisameasureofasystem’srandomnessordisorder.Enthalpyisrelatedtothechangeofheatcontentinareaction.Negativeenthalpiesindicateexothermicreactions.

15.(T,F)InthedecompositionofHgO,HgandO2aretheproducts.Theequationis2HgO→2Hg+O2(g)

Itisnotalwaystruethatthenumberofatomsofeachproductisequal.IthappensinthisreactionbecausethereisanequalnumberofatomsofHgandOintheformula.Indecomposingwateryouhave:2H2O→2H2(g)+O2(g)becausetherearetwiceasmanyatomsofhydrogenthanoxygenintheoriginalformula.

CHAPTER9

RatesofChemicalReactions

TheseskillsareusuallytestedontheSATSubjectTestinChemistry.Youshouldbeableto…•Explainhoweachofthefollowingfactorsaffecttherateofachemicalreaction:natureofthereactants,surfaceareaexposed,concentrations,temperature,andthepresenceofacatalyst.

•Drawreactiondiagramswithandwithoutacatalyst.•ExplaintheLawofMassAction.•Describetherelationshipbetweenreactionmechanismsandratesofreaction.This chapter will review and strengthen these skills. Be sure to do thePracticeExercisesattheendofthechapter.

Themeasurementofreactionrateisbasedontherateofappearanceofaproductor disappearance of a reactant. It is usually expressed in termsof a change inconcentrationofoneoftheparticipantsperunittime.Experiments have shown that for most reactions the concentrations of all

participants change most rapidly at the beginning of the reaction; that is, theconcentration of the products shows the greatest rate of increase, and theconcentrations of the reactants the highest rate of decrease, at this point. Thismeans that the rate of a reaction changeswith time.Therefore a ratemust beidentifiedwithaspecifictime.

FACTORSAFFECTINGREACTIONRATESFive important factors control the rate of a chemical reaction. These aresummarizedbelow.

TIP

Know the factors that affect reactionrates.

1.Thenatureofthereactants.Inchemicalreactions,somebondsbreakandothersform.Therefore,theratesofchemicalreactionsshouldbeaffectedbythenatureofthebondsinthereactingsubstances.Forexample,reactionsbetweenionsinanaqueoussolutionmaytakeplaceinafractionofasecond.Thus,thereactionbetweensilvernitrateandsodiumchlorideisveryfast.Thewhitesilverchlorideprecipitateappearsimmediately.Inreactionswheremanycovalentbondsmustbebroken,reactionusuallytakesplaceslowlyatroomtemperatures.Thedecompositionofhydrogenperoxideintowaterandoxygenhappensslowlyatroomtemperatures.Infact,about17minutesisrequiredforhalftheperoxideina0.50Msolutiontodecompose.

2.Thesurfaceareaexposed.Sincemostreactionsdependonthereactantscomingintocontact,thesurfaceexposedproportionallyaffectstherateofthereaction.

3.Theconcentrations.Thereactionrateisusuallyproportionaltotheconcentrationsofthereactants.Theusualdependenceofthereactionrateontheconcentrationofthereactantscansimplybeexplainedbytheorizingthat,ifmoremoleculesorionsofthereactantareinthereactionarea,thenthereisagreaterchancethatmorereactionswilloccur.Thisideaisfurtherdevelopedinthecollisiontheorydiscussedbelow.

4.Thetemperature.Atemperatureincreaseof10°Caboveroomtemperatureusuallycausesthereactionratetodoubleortriple.Thebasisforthisgeneralityisthat,asthetemperatureincreases,theaveragekineticenergyoftheparticlesinvolvedincreases.Asaresulttheparticlesmovefasterandhaveagreaterprobabilityofhittingotherreactantparticles.Becausetheparticleshavemoreenergy,theycancauseaneffectivecollision,resultinginthechemicalreactionthatformstheproductsubstance.

5.Thepresenceofacatalyst.Itisasubstancethatincreasesordecreasestherateofachemicalreactionwithoutitselfundergoinganypermanentchemicalchange.Thecatalystprovidesanalternativepathwaybywhichthereactioncanproceedandinwhichtheactivationenergyislower.Itthusincreasestherateatwhichthereactioncomestocompletionorequilibrium.

Generally,thetermisusedforasubstancethatincreasesreactionrate(apositivecatalyst).Somereactionscanbesloweddownbynegativecatalysts.

ACTIVATIONENERGYOftenareactionratemaybe increasedordecreasedbyaffecting theactivationenergy,thatis,theenergynecessarytocauseareactiontooccur.Thisisshowngraphicallybelowfortheforwardreaction.

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Activation energy is the energynecessary to cause a reaction tooccur.

A catalyst, as explained in the preceding section, is a substance that isintroduced intoa reaction to speedup the reactionbychanging theamountofactivationenergyneeded.Theeffectofacatalystusedtospeedupareactioncanbeshownasfollows:

TIP

A catalyst speeds up the reactionbutisnotconsumeditself.

REACTIONRATELAWThe relationship between the rate of a reaction and the masses (expressed asconcentrations) of the reacting substances is summarized in theLawofMassAction.Itstatesthattherateofachemicalreactionisproportionaltotheproductoftheconcentrationsofthereactants.ForageneralreactionbetweenAandB,representedby

aA+bB→…

theratelawexpressionis

or, inserting a constant of proportionality that mathematically changes theexpressiontoanequality,wehave

r=k[A]a[B]b

Herekiscalledthespecificrateconstantforthereactionatthetemperatureofthereaction.The exponents a and b may be added to give the total reaction order. For

example:

H2(g)+I2→2HI(g)r=k[H2]1[I2]1

The sumof theexponents is1+1=2, and thereforewehavea second-orderreaction.

ReactionMechanismandRatesofReactionThebeginningofthischapterstatedthatthereactionrateisusuallyproportionaltotheconcentrationsofthereactants.Thisoccursbecausesomereactionsdonotdirectlyoccurbetweenthereactantsbutmaygothroughintermediatestepstogettothefinalproduct.Theseriesofstepsbywhichthereactingparticlesrearrangethemselves to form the products of a chemical reaction is called the reactionmechanism.Forexample:

Step1 A+B → I1(fast)

Step2 A+I1 → I2(slow)

Step3 C+I2 → D(fast)Netequation 2A+B+C → D

Noticethatthereactionsofsteps1and3occurrelativelyfastcomparedwiththereactionofstep2.NowsupposethatweincreasetheconcentrationofC.Thiswillmake the reaction of step 3 go faster, but itwill have little effect on thespeed of the overall reaction since step 2 is the rate-determining step. If,however,theconcentrationofAisincreased,thentheoverallreactionratewillincrease because step 2will be accelerated.Knowing the reactionmechanismprovides the basis for predicting the effect of a concentration change of areactantontheoverallrateofreaction.Anotherwayofdeterminingtheeffectofconcentrationchangesisactualexperimentation.

ChapterSummaryThefollowingtermssummarizealltheconceptsandideasthatwereintroducedinthischapter.Youshouldbeabletoexplaintheirmeaningandhowyouwouldusetheminchemistry.Theyappearinboldfacetypeinthischaptertodrawyourattentiontothem.Theboldfacetypealsomakesiteasierforyoutolookthemupif you need to. You could also use the search or “Google” action on yourcomputer to get a quick and expanded explanation of these terms, laws, andformulas.

activationenergy factorsaffectingreactionratescatalyst LawofMassActioncollisiontheory reactionmechanism

InternetResourcesOnline content that reinforcesmajor concepts discussed in this chapter canbefound at the following Internet addresses if they are still available.Somemayhavebeenchangedordeleted.FactorsAffectingReactionRateshttp://www.chm.davidson.edu/ChemistryApplets/kinetics/index.htmlThis site offers you virtual experiments to demonstrate how factors affectreactionrates.

PracticeExercises

1.Listthefivefactorsthataffecttherateofareaction:

1.2.3.4.5.

2.Theadditionofacatalysttoareaction

(A)changestheenthalpy(B)changestheentropy(C)changesthenatureoftheproducts(D)changestheactivationenergy

3.Anincreaseinconcentration

(A)isrelatedtothenumberofcollisionsdirectly(B)isrelatedtothenumberofcollisionsinversely(C)hasnoeffectonthenumberofcollisions

4.Atthebeginningofareaction,thereactionrateforthereactantsis

(A)largest,thendecreasing(B)largestandremainsconstant(C)smallest,thenincreasing(D)smallestandremainsconstant

5.ThereactionratelawappliedtothereactionaA+bB→ABgivestheexpression

(A)r[A]b[B]a

(B)r[AB]a[A]b

(C)r[B]a[AB]b

(D)r[A]a[B]b

AnswersandExplanations1.(1)Natureofthereactants(2)Surfaceareaexposed(3)Concentrations(4)Temperature(5)Presenceofacatalyst

2.(D)Whenacatalystisaddedtoareaction,itisusedtoeitherincreaseordecreasetheactivationenergyneededforthereactiontooccur.Whentheactivationenergyisdecreased,itallowsthereactiontooccuratafasterrate;conversely,increasingtheactivationenergyslowsdowntheforwardreaction.

3.(A)Whentheconcentrationofreactantsisincreased,thenumberofcollisionsbetweenreactantsisdirectlyaffectedbecausetherearemorereactantunits(ions,atoms,ormolecules)available.

4.(A)Atthebeginningofareaction,thereactionrateofthereactantsisthehighestbecausetheirconcentrationisthehighest.Asthereactionprogresses,theconcentrationofthereactantsdecreaseswhiletheconcentrationoftheproductsincreases.

5.(D)ForthereactionaA+bB→AB,thereactionratelawwouldgivetheexpressionofrasproportionalto[A]a[B]b.

CHAPTER10

ChemicalEquilibrium

These skillsareusually testedon theSATSubjectTest inChemistry.Youshouldbeableto…

•Explainthedevelopmentofanequilibriumconditionandhowitisexpressedasanequilibriumconstant,anduseitmathematically.

•DescribeLeChâtelier’sPrincipleandhowchangesintemperature,pressure,andconcentrationsaffectanequilibrium.

•Solveproblemsdealingwithionizationofwater,findingthepH,solubilityproducts,andthecommonioneffect.

•ExplaintherelationshipofenthalpyandentropyasdrivingforcesinareactionandhowtheyarecombinedintheGibbsequation.

Thischapterwillreviewandstrengthentheseskills.BesuretodothePracticeExercisesattheendofthechapter.

Insomereactionsnoproductisformedtoallowthereactiontogotocompletion;thatis,thereactantsandproductscanstillinteractinbothdirections.Thiscanbeshownasfollows:

A+B C+D

ThedoublearrowindicatesthatCandDcanreacttoformAandB,whileAandBreacttoformCandD.

REVERSIBLEREACTIONSANDEQUILIBRIUMThereactionissaidtohavereachedequilibriumwhentheforwardreactionrateisequaltothereversereactionrate.Noticethatthisisadynamiccondition,NOTa static one, although in appearance the reaction seems to have stopped. Anexampleofanequilibriumisacrystalofcoppersulfateinasaturatedsolutionof

coppersulfate.Althoughtotheobserverthecrystalseemstoremainunchanged,thereisactuallyanequalexchangeofcrystalmaterialwiththecoppersulfateinsolution.Assomesolutecomesoutof solution,anequalamount isgoing intosolution.

TIP

Equilibrium is reached when theforwardandreversereactionrateareequal.

To express the rate of reaction in numerical terms,we can use theLaw ofMass Action, discussed in Chapter 9, which states: The rate of a chemicalreaction is proportional to the product of the concentrations of the reactingsubstances.Theconcentrationsareexpressedinmolesofgasperliterofvolumeormolesofsoluteperliterofsolution.Suppose,forexample,that1mole/literofgas A2 (diatomic molecule) is allowed to react with 1 mole/liter of anotherdiatomic gas, B2, and they form gas AB; let R be the rate for the forwardreaction forming AB. The bracketed symbols [A2] and [B2] represent theconcentrationsinmolesperliterforthesediatomicmolecules.ThenA2+B2→2ABhastherateexpression

R [A2]×[B2]

where is the symbol for “proportional to.”When [A2] and [B2] are both 1mole/liter,thereactionrateisacertainconstantvalue(k1)atafixedtemperature.

R=k1(k1iscalledtherateconstant)

ForanyconcentrationsofAandB,thereactionrateis

R=k1×[A2]×[B2]

If[A2]is3moles/literand[B2]is2moles/liter,theequationbecomes

R=k1×3×2=6k1

Thereactionrateissixtimesthevaluefora1mole/literconcentrationofeachreactant.At the fixed temperature of the forward reaction, AB molecules are also

decomposing.IfwedesignatethisreversereactionasR´,then,since

2AB(orAB+AB)→A2+B2

twomoleculesofABmustdecomposetoformonemoleculeofA2andoneofB2.ThusthereversereactioninthisequationisproportionaltothesquareofthemolecularconcentrationofAB:

wherek2 represents the rate of decompositionofABat the fixed temperature.Bothreactionscanbeshowninthismanner:

A2+B2 2AB(notedoublearrow)

When the first reactionbegins toproduceAB,someAB isavailable for thereversereaction.IftheinitialconditionisonlythepresenceofA2andB2gases,thentheforwardreactionwilloccurrapidlytoproduceAB.Astheconcentrationof AB increases, the reverse reaction will increase. At the same time, theconcentrationsofA2 andB2 will be decreasing and consequently the forwardreactionratewilldecrease.Eventuallythetworateswillbeequal,thatis,R=R´.Atthispoint,equilibriumhasbeenestablished,and

k1[A2]×[B2]=k2[AB]2

or

The convention is that k1 (forward reaction) is placed over k2 (reversereaction) to get this expression. Then k1/k2 can be replaced byKeq, which is

calledtheequilibriumconstantforthisreactionundertheparticularconditions.Inanothergeneralexample:

aA+bB cC+dDthereactionratescanbeexpressedas

Notethatthevaluesofk1andk2aredifferent,butthateachisaconstantfortheconditionsofthereaction.Atthestartofthereaction,[A]and[B]willbeattheirgreatestvalues,andRwillbe large; [C], [D],andR′willbezero.GraduallyRwill decrease and R′ will become equal. At this point the reverse reaction isforming theoriginal reactants just as rapidly as they arebeingusedupby theforward reaction. Therefore no further change in R, R´, or any of theconcentrationswilloccur.IfwesetR´equaltoR,wehave:

k2×[C]c×[D]d=k1×[A]a×[B]b

or

Thisprocessoftwosubstances,AandB,reactingtoformproductsCandDand the reverse can be shown graphically to represent what happens asequilibriumisestablished.Thehypotheticalequilibriumreactionisdescribedbythefollowinggeneralequation:

aA+bB cC+dDAtthebeginning(timet0),theconcentrationsofCandDarezeroandthose

ofAandBaremaximum.ThegraphbelowshowsthatovertimetherateoftheforwardreactiondecreasesasAandBareusedup.Meanwhile, therateof thereversereactionincreasesasCandDareformed.Whenthesetworeactionratesbecome equal (at time t1), equilibrium is established. The individualconcentrations of A, B, C, and D no longer change if conditions remain thesame.Toanobserver,itappearsthatallreactionhasstopped;infact,however,bothreactionsareoccurringatthesamerate.

TIP

Notice that as the forward reactionrate decreases, the reverse reactionrate increases until they are at“equilibrium.”

Weseethat,forthegivenreactionandthegivenconditions,Keqisaconstant,calledtheequilibriumconstant.IfKeqislarge,thismeansthatequilibriumdoesnotoccuruntiltheconcentrationsoftheoriginalreactantsaresmallandthoseoftheproductslarge.AsmallvalueofKeqmeansthatequilibriumoccursalmostatonceandrelativelylittleproductisproduced.Theequilibriumconstant,Keq,hasbeendeterminedexperimentallyformany

reactions,andthevaluesaregiveninchemicalhandbooks.SupposewefindKeqforreactingH2andI2at490°Ctobeequalto45.9.Then

theequilibriumconstantforthisreaction

H2(g)+I2(g) 2HI(g)at490°C

is

SAMPLEPROBLEM:ThreemolesofH2(g)and3.00molesofI2(g)areintroducedintoa1-literboxatatemperatureof490°C.Findtheconcentrationofeachsubstanceintheboxwhenequilibriumisestablished.

Initialconditions:

[H2]=3.00mol/L[I2]=3.00mol/L[HI]=0mol/L

Thereactionproceedstoequilibriumand

Atequilibrium,then,

[H2]=(3.00−x)mol/L

(wherexisthenumberofmolesofH2thatareintheformofHIatequilibrium)

[I2]=(3.00−x)mol/L

(thesamexisusedsince1molofH2requires1molofI2toreacttoform2molofHI)

[HI]=2xmol/L

Then

If

thentakingthesquarerootofeachsidegives

Solvingforx:

x=2.32

Note:OntheSATSubjectTestinChemistry,calculatorsarenotpermitted.Soanswerstoquestionslikethiswouldbeeasilycalculated“perfectsquares.”

Substituting this xvalue into the concentration expressions at equilibriumwehave

[H2]=(3.00−x)=0.68mol/L[I2]=(3.00−x)=0.68mol/L[HI]=2x=4.64mol/L

The crucial step in this type of problem is setting up your concentrationexpressionsfromyourknowledgeoftheequation.Supposethatthisproblemhadbeen:

SECONDSAMPLEPROBLEM:Findtheconcentrationsatequilibriumforthesameconditionsasintheprecedingexampleexceptthatonly2.00molesofHIareinjectedintothebox.

[H2]=0mol/L[I2]=0mol/L[HI]=2.00mol/L

Atequilibrium

[HI]=(2.00−x)mol/L

(ForeverymoleofHIthatdecomposes,only0.5moleofH2and0.5moleofI2areformed.)

[H2]=0.5x[I2]=0.5x

Solvingforxgives:

x=0.456

Then,substitutingintotheequilibriumconditions,

LECHÂTELIER’SPRINCIPLEAgeneral law,LeChâtelier’sPrinciple, canbeused to explain the resultsofapplyinganychangeof condition (stress)ona system in equilibrium. Itstatesthat if a stress is placed upon a system in equilibrium, the equilibrium isdisplacedinthedirectionthatcounteractstheeffectofthestress.Anincreaseinconcentrationofasubstancefavorsthereactionthatusesupthatsubstanceandlowers its concentration.A rise in temperature favors the reaction that absorbsheat and so tends to lower the temperature.These ideas are further developed

below.

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KnowLeChâtelier’sPrinciple.

EFFECTSOFCHANGINGCONDITIONSEffectofChangingtheConcentrationsWhen a system at equilibrium is disturbed by adding or removing one of thesubstances (thuschanging itsconcentration),all theconcentrationswillchangeuntilanewequilibriumpointisreachedwiththesamevalueofKeq.

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At equilibrium,Keq stays the sameatagiventemperature.

If the concentration of a reactant in the forward action is increased, theequilibrium is displaced to the right, favoring the forward reaction. If theconcentrationofareactantinthereversereactionisincreased,theequilibriumisdisplacedtotheleft.Decreasesinconcentrationwillproduceeffectsoppositetothoseproducedbyincreases.

EffectofTemperatureonEquilibriumIf the temperatureofagivenequilibriumreaction ischanged, thereactionwillshifttoanewequilibriumpoint.Ifthetemperatureofasysteminequilibriumisraised,theequilibriumisshiftedinthedirectionthatabsorbsheat.Notethattheshiftinequilibriumasaresultoftemperaturechangeisactuallyachangeinthevalueof theequilibriumconstant.This isdifferent fromtheeffectofchangingthe concentration of a reactant; when concentrations are changed, theequilibriumshiftstoaconditionthatmaintainsthesameequilibriumconstant.

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Know how each factor affectsequilibrium.

EffectofPressureonEquilibriumAchangeinpressureaffectsonlyequilibriainwhichagasorgasesarereactantsor products. Le Châtelier’s Law can be used to predict the direction ofdisplacement.Ifitisassumedthatthetotalspaceinwhichthereactionoccursisconstant, the pressure will depend on the total number of molecules in thatspace.Anincreaseinthenumberofmoleculeswillincreasepressure;adecreaseinthenumberofmoleculeswilldecreasepressure.If thepressureis increased,thereactionthatwillbefavoredis theonethatwill lowerthepressure, that is,decreasethenumberofmolecules.An example of the application of these principles is the Haber process of

makingammonia.Thereactionis

N2(g)+3H2(g) 2NH3(g)+heat(atequilibrium)

Iftheconcentrationsofthenitrogenandhydrogenareincreased,theforwardreactionisincreased.Atthesametime,iftheammoniaproducedisremovedbydissolvingitintowater,theforwardreactionisagainfavored.Because the reaction is exothermic, the additionof heatmust be considered

withcare.Increasingthetemperaturecausesanincreaseinmolecularmotionandcollisions,thusallowingtheproducttoformmorereadily.Atthesametime,theequilibriumequationshowsthatthereversereactionisfavoredbytheincreasedtemperature,soacompromisetemperatureofabout500°Cisusedtogetthebestyield.Anincreaseinpressurewillcausetheforwardreactiontobefavoredsincethe

equation shows that fourmoleculesof reactants are forming twomoleculesofproducts.Thiseffecttendstoreducetheincreaseinpressurebytheformationofmoreammonia.

EQUILIBRIAINHETEROGENEOUSSYSTEMSTheexamplessofarhaveinvolvedsystemsmadeupofonlygaseoussubstances.ExpressionoftheKvaluesofsystemschangeswhenotherphasesarepresent.

EquilibriumConstantforSystemsInvolvingSolids

Iftheexperimentaldataforthisreactionarestudied:

CaCO3(s) CaO(s)+CO2(g)

itisfoundthatatagiventemperatureanequilibriumisestablishedinwhichtheconcentrationofCO2 is constant. It is also true that the concentrations of thesolidshavenoeffectontheCO2concentrationaslongasbothsolidsarepresent.ThereforetheKeq,whichwouldconventionallybewrittenlikethis:

canbemodifiedbyincorporatingtheconcentrationsofthetwosolids.Thiscanbedonesincetheconcentrationofsolidsisfixed.ItbecomesanewconstantK,knownas:

K=[CO2]

Any heterogeneous reaction involving gases does not include theconcentrationsofpuresolids.Asanotherexample,Kforthereaction

NH4Cl(s) NH3(g)+HCl(g)is

K=[NH3][HCl]

AcidIonizationConstantsWhen aweak acid does not ionize completely in a solution, an equilibrium isreachedbetweentheacidmoleculeanditsions.Themassactionexpressioncanbeusedtoderiveanequilibriumconstant,calledtheaciddissociationconstant,forthiscondition.Forexample,anaceticacidsolutionionizingisshownas

HC2H3O2(l)+H2O(l) H3O+(aq)+C2H3O2−(aq)

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Kaincorporatestheconcentrationofwater.

Theconcentrationofwater inmoles/liter is foundbydividing themassof1literofwater(whichis1,000gat4°C)byitsgram-molecularmass,18grams,giving H2O a value of 55.6 moles/liter. Because this number is so largecompared with the other numbers involved in the equilibrium constant, it ispractically constant and is incorporated into a new equilibrium constant,designatedasKa.Thenewexpressionis

Ionizationconstantshavebeenfoundexperimentallyformanysubstancesandare listed in chemical tables. The ionization constants of ammonia and aceticacidareabout1.8×10−5.ForboricacidKa=5.8×10−10,andforcarbonicacidKa=4.3×10−7.If theconcentrationsoftheionspresentinthesolutionofaweakelectrolyte

are known, the value of the ionization constant canbe calculated.Also, if thevalueofKaisknown,theconcentrationsoftheionscanbecalculated.AsmallvalueforKameansthattheconcentrationoftheun-ionizedmolecule

must be relatively large compared with the ion concentrations. Conversely, alarge value forKameans that the concentrations of ions are relatively high.Therefore the smaller the ionization constant of an acid, the weaker the acid.Thus,ofthethreeacidsreferredtoabove,theionizationconstantsshowthattheweakest is boric acid, and the strongest, acetic acid. It should be rememberedthat, in all caseswhere ionization constants are used, the electrolytesmust beweakinordertobeinvolvedinionicequilibria.

IonizationConstantofWaterBecause water is a very weak electrolyte, its ionization constant can beexpressedasfollows:

2H2O(l) H3O+(aq)+OH−(aq)

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Kwincorporatesthe[H2O]2.

(Dissociationconstant)Kw=[H3O+][OH−]=1×10−14at25°C

From this expression,we see that fordistilledwater [H3O+]= [OH−]=1×10−7.ThereforethepH,whichis−log[H3O+],is

pH=−log[1×10−7]

pH=−[−7]=7foraneutralsolution

ThepHrangeof1to6isacid,andthepHrangeof8to14isbasic.Seethechartbelow.

SAMPLEPROBLEM:(Thissampleincorporatestheentirediscussionofdissociationconstants,includingfindingthepH.)

Calculate(a)the[H3O+],(b)thepH,and(c)thepercentagedissociationfor0.10Maceticacidat25°C.ThesymbolKaisusedfortheaciddissociationconstant.KaforHC2H3O2is1.8×10−5.

(a)Forthisreaction

H2O(l)+HC2H3O2(l) H3O+(aq)+C2H3O2−(aq)

and

Letx=numberofmoles/literofHC2H3O2thatdissociateandreachequilibrium.Then

[H3O+]=x,[C2H3O2−]=x,[HC2H3O2]=0.10−x

SubstitutingintheexpressionforKagives

Because a weak acid, such as acetic, at concentrations of 0.01 M or greaterdissociates very little, the equilibrium concentration of the acid is very nearlyequaltotheoriginalconcentration,thatis,

0.10−x 0.10

Therefore,theexpressioncanbechangedto

(b)SubstitutingthisresultinthepHexpressiongives

(c)Thepercentageofdissociationoftheoriginalacidmaybeexpressedas

SolubilityProductsAsaturatedsolutionofasubstancehasbeendefinedasanequilibriumconditionbetweenthesoluteanditsions.Forexample:

AgCl(s) Ag+(aq)+Cl−(aq)Theequilibriumconstantwouldbe:

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Kspincorporatestheconcentrationofthesolute.

Sincetheconcentrationofthesoluteremainsconstantforthattemperature,the[AgCl]isincorporatedintotheKtogivetheKsp,calledthesolubilityconstant:

Ksp=[Ag+][Cl−]=1.2×10−10at25°CThissetupcanbeusedtosolveproblemsinwhichtheionicconcentrationsaregivenandtheKspistobefoundortheKspisgivenandtheionicconcentrationsaretobedetermined.TYPEPROBLEM:FindingtheKsp.

ByexperimentationitisfoundthatasaturatedsolutionofBaSO4at25°Ccontains3.9×10−5

mole/literofBa2+ions.FindtheKspofthissalt.SinceBaSO4ionizesintoequalnumbersofBa2+andSO4

2−,thebariumionconcentrationwillequalthesulfateionconcentration.Thenthesolutionis

BaSO4 Ba2+(aq)+SO42−(aq)

and

Ksp=[Ba2+][SO42−]

Therefore

Ksp=(3.9×10−5)(3.9×10−5)=1.5×10−9

ANOTHERTYPEFindingthesolubility.PROBLEM:

IftheKspofradiumsulfate,RaSO4,is4×10−11,calculatethesolubilityofthecompoundinpurewater.Letx=molesofRaSO4thatdissolveperliterofwater.Then,inthesaturatedsolution,

[Ra2+]=xmol/L[SO4

2−]=xmol/LRaSO4(s) Ra2+(aq)+SO4

2−(aq)[Ra2+][SO4

2−]=Ksp=4×10−11

Letx=[Ra2+]and[SO42−].Then

(x)(x)=4×10−11=40×10−12

(x)=6×10−6mol/L

ThusthesolubilityofRaSO4is6×10−6mole/literofwater,forasolution6×10−6MinRa2+and6×10−6

MinSO42−.

ANOTHERTYPEPredictingtheformationofaprecipitate.PROBLEM:

Insomecases,thesolubilityproductsofsolutionscanbeusedtopredicttheformationofaprecipitate.

Supposewehavetwosolutions.Onesolutioncontains1.00×10−3moleofsilvernitrate,AgNO3,

perliter.Theothersolutioncontains1.00×10−2moleofsodiumchloride,NaCl,perliter.If1literoftheAgNO3solutionand1literoftheNaClsolutionaremixedtomakea2-litermixture,willaprecipitateofAgClform?

IntheAgNO3solution,theconcentrationsare:[Ag+]=1.00×10−3mol/Land[NO3

−]=1.00×10−3mol/L

IntheNaClsolution,theconcentrationsare:[Na+]=1.00×10−2mol/Land[Cl−]=1.00×10−2mol/L

When1literofoneofthesesolutionsismixedwith1literoftheothersolutiontoformatotalvolumeof2liters,theconcentrationswillbehalved.

Inthemixturethen,theinitialconcentrationswillbe:

[Ag+]=0.50×10−3or5.0×10−4mol/L[Cl−]=0.50×10−2or5.0×10−3mol/L

FortheKspofAgCl,

[Ag+][Cl−]=[5.0×10−4][5.0×10−3][Ag+][Cl−]=25×10−7or2.5×10−6

This is far greater than 1.7 × 10−10, which is the Ksp of AgCl. Theseconcentrationscannotexist,andAg+andCl−willcombine to formsolidAgClprecipitate.OnlyenoughAg+ionsandCl−ionswillremaintomaketheproductoftherespectiveionconcentrationsequal1.7×10−10.

COMMONIONEFFECTWhena reactionhas reachedequilibrium, andanoutside source addsmoreofone of the ions that is already in solution, the result is to cause the reverse

reaction tooccurat a faster rateand reestablish theequilibrium.This is calledthecommonioneffect.Forexample,inthisequilibriumreaction:

NaCl(s) Na+(aq)+Cl−(aq)theadditionofconcentratedHCl(12M)addsH+andCl−bothataconcentrationof12M.ThisincreasestheconcentrationoftheCl−anddisturbstheequilibrium.The reactionwill shift to the left and cause some solid NaCl to come out ofsolution.The “common” ion is the one already present in an equilibrium before a

substance isadded that increases theconcentrationof that ion.Theeffect is toreverse the solution reaction and to decrease the solubility of the originalsubstance,asshownintheaboveexample.

DRIVINGFORCESOFREACTIONSRelationofMinimumEnergy(Enthalpy)toMaximumDisorder(Entropy)Somereactionsaresaidtogotocompletionbecausetheequilibriumconditionisachievedwhenpracticallyallthereactantshavebeenconvertedtoproducts.Attheotherextreme,somereactionsreachequilibriumimmediatelywithverylittleproduct being formed. These two examples are representative of very largeKvaluesandverysmallKvalues, respectively.Thereareessentially twodrivingforcesthatcontroltheextentofareactionanddeterminewhenequilibriumwillbeestablished.Thesearethedrivetothelowestheatcontent,orenthalpy,andthe drive to the greatest randomness or disorder, which is called entropy.Reactions with negative ΔH’s (enthalpy or heat content) are exothermic, andreactionswithpositiveΔS’s(entropyorrandomness)areproceedingtogreaterrandomness.TheSecondLawofThermodynamicsstatesthattheentropyoftheuniverse

increasesforanyspontaneousprocess.Thismeansthattheentropyofasystemmay increase or decrease but that, if it decreases, then the entropy of thesurroundingsmust increasetoagreaterextentsothat theoverallchangeintheuniverseispositive.Inotherwords,

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When the ΔS is positive for thesystem,itmeansgreaterdisorder.

ThefollowingisalistofconditionsinwhichΔSispositiveforthesystem:

1.Whenagasisformedfromasolid,forexample,

CaCO3(s)→CaO(s)+CO2(g).

2.Whenagasisevolvedfromasolution,forexample,

Zn(s)+2H+(aq)→H2(g)+Zn2+(aq).

3.Whenthenumberofmolesofgaseousproductexceedsthemolesofgaseousreactant,forexample,

2C2H6(g)+7O2→4CO2(g)+6H2O(g).

4.Whencrystalsdissolveinwater,forexample,

NaCl(s)→Na+(aq)+Cl−(aq).Looking at specific examples, we find that in some cases endothermic

reactions occur when the products provide greater randomness or positiveentropy.Thisreactionisanexample:

CaCO3(s) CaO(s)+CO2(g)

Theproductionofthegasandthusgreaterentropymightbeexpectedtotakethisreactionalmosttocompletion.However,thisdoesnotoccurbecauseanotherforce is hampering this reaction. It is the absorption of energy, and thus theincreaseinenthalpy,astheCaCO3isheated.Theequilibriumcondition,then,ataparticulartemperature,isacompromise

betweentheincreaseinentropyandtheincreaseinenthalpyofthesystem.The Haber process of making ammonia is another example of this

compromiseofdrivingforcesthataffecttheestablishmentofanequilibrium.In

thisreaction

N2(g)+3H2(g) 2NH3(g)+heat

the forward reaction to reach the lowest heat content and thus release energycannotgo tocompletionbecause the force tomaximumrandomness isdrivingthereversereaction.

ChangeinFreeEnergyofaSystem—theGibbsEquationThese factors, enthalpy and entropy, can be combined in an equation thatsummarizes the changeof free energy in a system.This is designated asΔG.Therelationshipis

ΔG=ΔH−TΔS(Tistemperatureinkelvins)andiscalledtheGibbsfree-energyequation.

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Free energy, ΔG, depends on ΔH(enthalpy)andΔS(entropy).

ThesignofΔGcanbeusedtopredictthespontaneityofareactionatconstanttemperature and pressure. If ΔG is negative, the reaction is (probably)spontaneous; ifΔG is positive, the reaction is improbable; and ifΔG is 0, thesystemisatequilibriumandthereisnonetreaction.Theways inwhich the factors in the equation affect ΔG are shown in this

table:

This drive to achieve aminimum of free energymay be interpreted as thedrivingforceofachemicalreaction.

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Knowtheserelationships.

ChapterSummaryThefollowingtermssummarizealltheconceptsandideasthatwereintroducedinthischapter.Youshouldbeabletoexplaintheirmeaningandhowyouwouldusetheminchemistry.Theyappearinboldfacetypeinthischaptertodrawyourattentiontothem.Theboldfacetypealsomakesiteasierforyoutolookthemupif you need to. You could also use the search or “Google” action on yourcomputer to get a quick and expanded explanation of these terms, laws, andformulas.

acidionizationconstant equilibriumconstantcommonioneffect freeenergyenthalpy(ΔH) Gibbsfree-energyequationentropy(ΔS) solubilityproductconstantequilibriumLeChâtelier’sPrincipleSecondLawofThermodynamics

InternetResources

Online content that reinforcesmajor concepts discussed in this chapter canbefound at the following Internet addresses if they are still available.Somemayhavebeenchangedordeleted.LeChâtelier’sPrinciplehttp://www.ausetute.com.au/lechatsp.htmlThis sitegives anexplanationof theprinciple.This site alsoprovides specificexamplesofhowtheprinciplecanbeusedindifferentcircumstancestoshowthe

effectsofchanging temperature,pressure, andconcentrationonanequilibriumsystem.EquilibriumEquationsandConstantshttp://www.800mainstreet.com/7/0007-007-Equi_exp_k.htmlThis site offers tutorials and exercises on how to work with equilibriumequations and constants along with exercises and answers to equilibriumproblems.Entropyhttp://www.2ndlaw.com/Thissiteoffersauniqueapproachtoinvestigateentropyandthesecondlawofthermodynamicsasadialoguebetweenastudentandteacher.

PracticeExercises1.ForthereactionA+B C+D,theequilibriumconstantcanbeexpressedas:

(A)

(B)

(C)

(D)

2.Theconcentrationsinanexpressionoftheequilibriumconstantaregivenin

(A)mol/mL(B)g/L(C)gram-equivalents/L(D)mol/L

3.Intheequilibriumexpressionforthereaction

BaSO4(s) Ba2+(aq)+SO42−(aq)

Kspisequalto

(A)[Ba2+][SO42−]

(B)

(C)

(D)

4.TheKwofwaterat298Kisequalto

(A)1×10−7

(B)1×10−17

(C)1×10−14

(D)1×10−1

5.ThepHofasolutionthathasahydrogenionconcentrationof1×10−4mole/literis

(A)4(B)-4(C)10(D)-10

6.ThepHofasolutionthathasahydroxideionconcentrationof1×10−4mole/literis

(A)4(B)-4(C)10(D)-10

7.AsmallvalueforK,theequilibriumconstant,indicatesthat

(A)theconcentrationoftheun-ionizedmoleculesmustberelativelysmallcomparedwiththeionconcentrations

(B)theconcentrationoftheionizedmoleculesmustbelargerthantheion

concentrations(C)thesubstanceionizestoalargedegree(D)theconcentrationoftheun-ionizedmoleculesmustberelativelylarge

comparedwiththeionconcentrations

8.IntheHaberprocessformakingammonia,anincreaseinpressurefavors

(A)theforwardreaction(B)thereversereaction(C)neitherreaction

9.AchangeinwhichoftheseconditionswillchangetheKofanequilibriumgivenasastartingpoint?

(A)Temperature(B)Pressure(C)Concentrationofreactants(D)Concentrationofproducts

10.IfCa(OH)2isdissolvedinasolutionofNaOH,itssolubility,comparedwiththatinpurewater,is

(A)increased(B)decreased(C)unaffected

ThefollowingquestionsareintheformatthatisusedontheSATSubjectAreaTestinChemistry.Ifyouarenotfamiliarwiththesetypesofquestions,studybeforedoingtheremainderofthereviewquestions.

Directions:The following set of lettered choices refers to the numberedquestions immediatelybelow it.For eachnumbered item,choose theoneletteredchoice that fits itbest.Everychoice in thesetmaybeusedonce,morethanonce,ornotatall.

Questions11–15

(A)thefreeenergyisalwaysnegative

(B)thefreeenergyisnegativeatlowertemperatures(C)thefreeenergyisnegativeathightemperatures(D)thefreeenergyisnevernegative(E)thesystemisatequilibrium,andthereisnonetreaction

Completethesentencewiththeappropriatechoice.

11.Whenenthalpyisnegativeandentropyispositive,12.Whenenthalpyispositiveandentropyispositive,13.Whenenthalpyisnegativeandentropyisnegative,14.Whenenthalpyispositiveandentropyisnegative,15.WhenΔG,freeenergy,iszero,

AnswersandExplanations1.(C)ThecorrectsetupofKeqistheproductoftheconcentrationoftheproductsovertheproductsofthereactants.

2.(D)Theconcentrationsinanexpressionoftheequilibriumconstantaregiveninmoles/liter(mol/L).

3.(A)Thisreactionistheequilibriumbetweenaprecipitateanditsionsinsolution.BecauseBaSO4isasolid,itdoesnotappearinthesolubilityproductexpression.Therefore,Ksp=[Ba+2][SO4

2−].

4.(C)ThisistheKexpressionofwater.

5.(A)BecausethepHisdefinedasthenegativeofthelogoftheH+

concentration,itis-(logof10−4),whichis-(-4)or4.

6.(C)pH+pOH=14.Inthisproblem,thepOH=-log[OH]=-log[10−4]=-(-4)=4.Placingthisvalueintheequation,youhavepH+4=14.SolvingforpH,youget10.

7.(D)ForKeqtobeasmallvalue,thenumeratoroftheexpressionmustbesmallcomparedwiththedenominator.Becausethenumeratoristheproductoftheconcentrationsoftheionconcentrationsandthedenominatoristheproductoftheun-ionizedmolecules,theconcentrationoftheun-ionizedmoleculesmustberelativelylargecomparedwiththeionconcentrations.

8.(A)Inthereactionfortheformationofammonia,N2+3H2↔2NH3+heat(atequilibrium).Anincreaseinpressurewillcausetheforwardreactiontobefavored,becausetheequationshowsthatfourmoleculesofreactantsareformingtwomoleculesofproducts.Thiseffecttendstoreducethisincreaseinpressurebytheformationofmoreammonia.

9.(A)OnlythechangingofthetemperatureoftheequilibriumreactionwillchangetheKoftheequilibriumgivenatthestartingpoint.

10.(B)Becausetherealreadyisaconcentrationof(OH)-ionsfromtheNaOHinsolution,thiscommonioneffectwilldecreasethesolubilityoftheCa(OH)2.

11.(A)Whenenthalpyisnegativeandentropyispositive,thefreeenergyisalwaysnegative.

12.(C)Whenenthalpyispositiveandentropyispositive,thefreeenergyisnegativeathightemperatures.

13.(B)Whenenthalpyisnegativeandentropyisnegative,thefreeenergyisnegativeatlowertemperatures.

14.(D)Whenenthalpyispositiveandentropyisnegative,thefreeenergyisnevernegative.

15.(E)WhenΔG,freeenergy,iszero,thesystemisatequilibriumandthereisnonetreaction.

CHAPTER11

Acids,Bases,andSalts

TheseskillsareusuallytestedontheSATSubjectTestinChemistry.Youshouldbeableto…•DescribethepropertiesofanArrheniusacidandbase,andknowthename,formula,anddegreeofionizationofcommonacidsandbases.

•ExplaintheBrønsted-LowryTheoryofacidsandconjugatebases.•DrawexamplesandexplaintheLewisTheoryofacids–bases.•DeterminepHandpOHofsolutions.•Solvetitrationproblemsandtheuseofindicatorsintheprocess.•Describehowabufferworks.•Explaintheformationandnamingofsalts.•Explainamphotericsubstancesinrelationtoacid–basetheory.This chapter will review and strengthen these skills. Be sure to do thePracticeExercisesattheendofthechapter.

Whatdefinesanacid?Abase?Asalt?Youmustknowthedifferentways thattheseinteract.YoumustalsoknowhowtodeterminethepHofasubstanceandhowtoneutralizethatsamesubstance.

DEFINITIONSANDPROPERTIESAcidsTherearesomecharacteristicpropertiesbywhichanacidmaybedefined.Themostimportantare:

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Learn these characteristics ofcommonacids.

1.Water(aqueous)solutionsofacidsconductelectricity.Thedegreeofconductiondependsontheacid’sdegreeofionization.Afewacidsionizealmostcompletely,whileothersionizetoonlyaslightdegree.Thetablebelowindicatessomecommonacidsandtheirdegreesofionization.

2.Acidswillreactwithmetalsthataremoreactivethanhydrogenionstoliberatehydrogen.(Someacidsarealsostrongoxidizingagentsandwillnotreleasehydrogen.Somewhatconcentratednitricacidissuchanacid.)

3.Acidshavetheabilitytochangethecolorofindicators.Somecommonindicatorsarelitmusandphenolphthalein.Litmusisadyestuffobtainedfromplantlife.Whenlitmusisaddedtoanacidicsolution,orpaperimpregnatedwithlitmusisdippedintoanacid,theneutralpurplecolorchangestopink-red.Phenolphthaleinispinkinabasicsolutionandbecomescolorlessinaneutraloracidsolution.

4.Acidsreactwithbasessothatthepropertiesofbotharelosttoformwaterandasalt.Thisiscalledneutralization.Thegeneralequationis:

Acid+Base→Salt+Water

Anexampleis:

Mg(OH)2(aq)+H2SO4(aq)→MgSO4(aq)+2H2O(l)

5.Acidsreactwithcarbonatestoreleasecarbondioxide.Anexample:

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Learn the names and formulas ofthesecommonacids.

The most common theory used in first-year chemistry is the ArrheniusTheory,whichstatesthatanacidisasubstancethatyieldshydrogenionsinanaqueoussolution.Althoughwespeakofthesehydrogenionsinthesolution,theyarereallynotseparateionsbutbecomeattachedtotheoxygenofthepolarwatermolecule to form the H3O+ ion (the hydronium ion). Thus, it is really thishydroniumionweareconcernedwithinanacidsolution.Thegeneralreactionforthedissociationofanacid,HX,iscommonlywritten

asHX H++X−

Toshowtheformationofthehydroniumion,H3O+,thecompleteequationis:HX+H2O H3O++X−

AlistofcommonacidsandtheirformulasisgiveninChapter4,Table7;anexplanationofthenamingproceduresforacidsprecedesTable7.

BasesBasesmay also be defined by some operational definitions that are based onexperimentalobservations.Someoftheimportantonesareasfollows:

1.Basesareconductorsofelectricityinanaqueoussolution.Theirdegreesofconductiondependontheirdegreesofionization.Thedegreesofionizationofsomecommonbasesareshowninthetablebelow.

2.Basescauseacolorchangeinindicators.Litmuschangesfromredtoblueinabasicsolution,andphenolphthaleinturnspinkfromitscolorlessstate.

3.Basesreactwithacidstoneutralizeeachotherandformasaltandwater.

4.Basesreactwithfatstoformaclassofcompoundscalledsoaps.Earliergenerationsusedthismethodtomaketheirownsoap.

5.Aqueoussolutionsofbasesfeelslippery,andthestrongerbasesareverycaustictotheskin.

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Learn the names and formulas ofthesecommonbases.

TheArrhenius Theory defines a base as a substance that yields hydroxideions(OH−)inanaqueoussolution.Somecommonbaseshavefamiliarnames,forexample:

Sodiumhydroxide =lye,causticsodaPotassiumhydroxide =causticpotashCalciumhydroxide =slakedlime,hydratedlime,limewaterAmmoniumhydroxide =ammoniawater,householdammonia

Muchof the sodiumhydroxideproduced todaycomes from theHookercellelectrolysis apparatus.The electrolysis process for the decomposition ofwaterwas discussed in Chapter 7. When an electric current is passed through a

saltwater solution,hydrogen,chlorine, andsodiumhydroxideare theproducts.Theformulaforthisequationis:

BroaderAcid-BaseTheoriesBesidesthecommonArrheniusTheoryofacidsandbasesdiscussedforaqueoussolutions,twoothertheories,theBrønsted-LowryTheoryandtheLewisTheory,arewidelyused.

TheBrønsted-LowryTheory(1923)definesacidsasprotondonorsandbasesasprotonacceptors.Thisdefinitionagreeswiththeaqueoussolutiondefinitionofanacidgivinguphydrogenionsinsolution,butgoesbeyondtoothercasesaswell.An example is the reaction of dry HCl gas with ammonia gas to form the

whitesolidNH4Cl.

HCl(g)NH3(g)→NH4+(s)+Cl−(s)

TheHClistheprotondonororacid,andtheammoniaisaBrønsted-Lowrybasethatacceptstheproton.

ConjugateAcidsandBases

In an acid–base reaction, the original acid gives up its proton to become aconjugate base. In other words, after losing its proton, the remaining ion iscapableofgainingaproton,thusqualifyingasabase.Theoriginalbaseacceptsa proton, so it now is classified as a conjugate acid since it can release thisnewlyacquiredprotonandthusbehavelikeanacid.Someexamplesaregivenbelow:

StrengthofConjugateAcidsandBasesTheextentofthereactionbetweenaBrønsted-Lowryacidandbasedependsonthe relative strengths of the acids and bases involved. Consider the followingexample.Hydrochloric is a strong acid. It gives up protons readily. It followsthat theCl–ionhas little tendency to attract and retain aproton.Consequently,theCl–ionisanextremelyweakbase.

Thisobservationleadstoanimportantconclusion:thestrongeranacidis,theweakeritsconjugatebase;thestrongerabaseis,theweakeritsconjugateacid.This concept allows strengths of different acids and bases to be compared topredict the outcome of a reaction. As an example, consider the reaction ofperchloricacid,HClO4,andwater.

Another important general conclusion is that proton-transfer reactions favorthe production of the weaker acid and the weaker base. For a reaction toapproachcompletion, the reactantsmustbemuch stronger as anacidandasabasethantheproducts.

TheLewisTheory(1916)definesacidsandbasesintermsoftheelectron-pairconcept,whichisprobablythemostgenerallyusefulconceptofacidsandbases.According to the Lewis definition, an acid is an electron-pair acceptor; and abaseisanelectron-pairdonor.Anexampleistheformationofammoniumionsfromammoniagasandhydrogenions.

Notice that the hydrogen ion is in fact accepting the electron pair of theammonia,soitisaLewisacid.Theammoniaisdonatingitselectronpair,soitisaLewisbase.Anotherexampleisborontrifluoride.ItisanexcellentLewisacid.Itformsa

fourthcovalentbondwithmanymoleculesandions.Itsreactionwithafluorideionisshownbelow.

BF3(aq)+F−(aq)→BF4−(aq)

Theacid–basesystemsaresummarizedbelow.

Type Acid BsseArrhenius H+orH3O+producer OH–producerBrønsted-Lowry proton(H+)donor proton(H+)acceptorLewis electron-pairacceptor electron-pairdonor

AcidConcentrationExpressedaspHFrequently, acid and base concentrations are expressed by means of the pHsystem.ThepHcanbedefinedas−log[H+],where[H+]istheconcentrationofhydrogenionsexpressedinmolesperliter.Thelogarithmistheexponentof10whenthenumberiswritteninthebase10.Forexample:

100=102sologarithmof100,base10=210,000=104sologarithmof10,000,base10=4

0.01=10−2sologarithmof0.01,base10=-2

Thelogarithmsofmorecomplexnumberscanbefoundinalogarithmtable.AnexampleofapHproblemis:

FindthepHofa0.1molarsolutionofHCl.1ststep.BecauseHClionizesalmostcompletelyintoH+andCl−,[H+]=0.1

mole/liter.2ndstep.Bydefinition

pH=−log[H+]so

pH=−log[10−1]3rdstep.Thelogarithmof10−1is−1so

pH=−(−1)4thstep.ThepHthenis1.

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Remember:pH=−log[H3O+]

BecausewaterhasanormalH+concentrationof10−7mole/literbecauseoftheslightionizationofwatermolecules,thewaterpHis7whenthewaterisneitheracidnorbase.ThenormalpHrangeisfrom0to14.

ThepOHisthenegativelogarithmofthehydroxideionconcentration:

pOH=−log[OH−]

If the concentration of the hydroxide ion is 10−9 M, then the pOH of thesolutionis+9.

Fromtheequation

[H+][OH−]=1.0×10−14at298K

thefollowingrelationshipcanbederived:

pH+pOH=14.00

Inotherwords,thesumofthepHandpOHofanaqueoussolutionat298Kmustalwaysequal14.00.Forexample,ifthepOHofasolutionis9.00,thenitspHmustbe5.00.

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Remember:pH+pOH=14

SAMPLEPROBLEM:WhatisthepOHofasolutionwhosepHis3.0?Substituting3.0forpHintheexpressionpH+pOH=14.0

gives

3.0+pOH=14.0pOH=14.0-3.0pOH=11.0

INDICATORSSome indicators can be used to determine pH because of their color changessomewhere along this pH scale.Somecommon indicators and their respectivecolorchangesaregivenbelow.

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Notice that each indicator has itsownrangeofcolorchange.

Hereisanexampleofhowtoreadthischart:AtpHvaluesbelow4.5,litmusisred;above8.3,itisblue.Betweenthesevalues,itisamixtureofthetwocolors.In choosing an indicator for a titration, we need to consider if the solution

formedwhentheendpointisreachedhasapHof7.Dependingonthetypeofacidandbaseused,theresultinghydrolysisofthesaltformedmaycauseittobeslightlyacidic,slightlybasic,orneutral.Ifthetitrationisofastrongacidandastrongbase, theendpointwillbeatpH7andpracticallyany indicatorcanbeused.Thisisbecausetheadditionof1dropofeitherreagentwillchangethepHattheendpointbyabout6units.Fortitrationsofstrongacidsandweakbases,weneedanindicator,suchasmethylorange,thatchangescolorbetween3.1and4.4intheacidregion.Inthetitrationofaweakacidandastrongbase,weshoulduse an indicator that changes in the basic range. Phenolphthalein is a suitablechoice for this typeof titrationbecause it changes color in thepH8.3 to10.0range.

TITRATION—VOLUMETRICANALYSISKnowledgeoftheconcentrationsofsolutionsandthereactionstheytakepartincanbeused todetermine theconcentrationsof“unknown”solutionsor solids.Theuseofvolumemeasurementinsolvingtheseproblemsiscalledtitration.Acommonexampleofatitrationusesacid-basereactions.Ifyouaregivena

base of known concentration, that is, a standard solution, let us say 0.10 MNaOH, and youwant to determine the concentration of anHCl solution, youcouldtitratethesolutionsinthefollowingmanner.

First,introduceameasuredquantity,25.0milliliters,oftheNaOHintoaflaskbyusingapipetorburetteinasetupliketheoneintheaccompanyingdiagram.Next, introduce 2 drops of a suitable indicator. Because NaOH and HCl areconsidered a strong base and a strong acid, respectively, an indicator thatchanges color in the middle pH range would be appropriate. Litmus solutionwouldbeonechoice.Itisblueinabasicsolutionbutchangestoredwhenthesolutionbecomesacidic.SlowlyintroducetheHCluntilthecolorchangeoccurs.Thispoint iscalledtheendpoint.Thepointatwhichenoughacid isadded toneutralizeallthestandardsolutionintheflaskiscalledtheequivalencepoint.

BuretteSetupforTitration

Suppose21.5millilitersofHClwasneededtoproducethecolorchange.Thereactionthatoccurredwas

H+(aq)+OH−(aq)→H2O(l)

untilalltheOH−wasneutralized;thentheexcessH+causedthelitmuspapertochangecolor.TosolvethequestionoftheconcentrationofNaOH,thisequationisused:

Macid+Vacid=Mbase+Vbase

Substitutingtheknownamountsinthisequationgives

xMacid×21.5mL=0.1M×25.0mLx=0.116M

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Foratitration:Macid+Vacid=Mbase+Vbase

In choosing an indicator for a titration, we need to consider whether thesolutionformedwhentheendpointisreachedhasapHof7.Dependingonthetypes of acid and base used, the resulting hydrolysis of the salt formed maycausethesolutiontobeslightlyacidic,slightlybasic,orneutral.Ifastrongacidandastrongbasearetitrated,theendpointwillbeatpH7,andpracticallyanyindicatorcanbeusedbecauseadding1dropofeitherreagentwillchangethepHattheendpointbyabout6units.Fortitrationsofstrongacidsandweakbases,weneedanindicator,suchasmethylorange,thatchangescolorbetween3.1and4.4intheacidregion.Whentitratingaweakacidandastrongbase,weshoulduseanindicatorthatchangesinthebasicrange.Phenolphthaleinisthesuitablechoice for this typeof titrationbecause it changes color in thepH8.3 to10.0range.The process of the neutralization reaction can be represented by a titration

curveliketheonebelow,whichshowsthetitrationofastrongacidwithastrongbase.

EXAMPLE1:Findtheconcentrationofaceticacidinvinegarif21.6millilitersof0.20MNaOHisneededtotitratea25-millilitersampleofthevinegar.SolutionUsingtheequationMacid×Vacid=Mbase×Vbase,wehave

Anothertypeoftitrationprobleminvolvesasolidandatitratedsolution.

EXAMPLE2:AsolidmixturecontainsNaOHandNaCl.If10.0millilitersof0.100MHClisrequiredtotitratea0.100-gramsampleofthismixturetoitsendpoint,whatisthepercentofNaOHinthesample?

Solution

Since

then

SubstitutingtheHClinformationintheequation,wehave

(Note:thisis10mLexpressedinliters)

Since1molofHClneutralizes1molofNaOH,0.001molofNaOHmustbepresentinthemixture.Since1molNaOH=40.0g

then

0.001mol×40.0g/mol=0.04gNaOH

Therefore0.04gofNaOHwasinthe0.100-gsampleofthesolidmixture.Thepercentis0.04g/0.100g×100=40%.

In the explanations given to this point, the reactions that took place werebetween monoprotic acids (single hydrogen ions) and monobasic bases (onehydroxide ion per base). This means that each mole of acid had 1 mole ofhydrogen ions available, andeachmoleofbasehad1moleofhydroxide ionsavailable,tointeractinthefollowingreactionuntiltheendpointwasreached:

H+(aq)+OH−(aq)→2H2O(l)

Thisisnotalwaysthecase,however,anditisimportanttoknowhowtodealwithacidsandbasesthathavemorethanonehydrogenionandmorethanone

hydroxideionperformula.Thefollowingisanexampleofsuchaproblem.

EXAMPLE3:If20.0millilitersofanaqueoussolutionofcalciumhydroxide,Ca(OH)2,isusedinatitration,andanappropriateindicatorisaddedtoshowtheneutralizationpoint(endpoint),thefewdropsofindicatorthatareaddedcanbeignoredinthevolumeconsiderations.Therefore,if25.0millilitersofstandard0.050MHClisrequiredtoreachtheendpoint,whatwastheoriginalconcentrationoftheCa(OH)2solution?Thebalancedequationforthereactiongivestherelationshipbetweenthenumberofmolesofacidreactingandthenumberofmolesofbase:

The mole relationship here is that the number of moles of acid is twice thenumberofmolesofbase:

No.ofmolesofacid=2×No.ofmolesofbase↑molefactor

Sincethemolarconcentrationoftheacidtimesthevolumeoftheacidgivesthenumberofmolesofacid:

Ma×Va=molesofacid

andthemolarconcentrationofthebasetimesthevolumeofthebasegivesthenumberofmolesofbase:

Mb×Vb=moleofbase

then,substitutingtheseproductsintothemolerelationship,weget

MaVa=2MbVb

SolvingforMbgives

Substitutingvalues,weget

BUFFERSOLUTIONSBuffer solutions are equilibrium systems that resist changes in acidity andmaintain constant pH when acids or bases are added to them. A typicallaboratorybuffer canbepreparedbymixing equalmolar quantities of aweakacidsuchasHC2H3O2anditssalt,NaC2H3O2.WhenasmallamountofastrongbasesuchasNaOHisaddedtothebuffer,theaceticacidreacts(andconsumes)mostoftheexcessOH−ion.TheOH−ionreactswiththeH+ionfromtheaceticacid,thusreducingtheH+ionconcentrationinthisequilibrium:

ThisreductionofH+causesashift to theright, formingadditionalC2H3O2−

ionsandH+ ions.Forpracticalpurposes,eachmoleofOH−addedconsumes1moleofHC2H3O2andproduces1moleofC2H3O2

−ions.WhenastrongacidsuchasHClisaddedtothebuffer,theH+ionsreactwith

theC2H3O2−ionsofthesaltandformmoreundissociatedHC2H3O2.Thisdoes

not alter theH+ ion concentration. Proportional increases and decreases in theconcentrationsofC2H3O2

−andHC2H3O2donotsignificantlyaffecttheacidityofthesolution.

SALTSAsalt isan ioniccompoundcontainingpositive ionsother thanhydrogen ionsandnegative ionsother thanhydroxide ions.Theusualmethodofpreparing aparticular salt is byneutralizing the appropriate acid andbase to form the saltandwater.

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Therearefivemethodsforpreparingsalts.

Fivemethodsforpreparingsaltsareasfollows:

1.Neutralizationreaction.Anacidandabaseneutralizeeachothertoformtheappropriatesaltandwater.Forexample:

2.Singlereplacementreaction.Anactivemetalreplaceshydrogeninanacid.Forexample:

Mg(s)+H2SO4(aq)→MgSO4(aq)+H2(g)

3.Directcombinationofelements.Anexampleofthismethodisthecombinationofironandsulfur.Inthisreactionsmallpiecesofironareheatedwithpowderedsulfur:

4.Doublereplacement.Whensolutionsoftwosolublesaltsaremixed,theyformaninsolublesaltcompound.Forexample:

AgNO3(aq)+NaCl(aq)→NaNO3(aq)+AgCl(s)

5.Reactionofametallicoxidewithanonmetallicoxide.Forexample:

MgO(s)+SiO2(s)→MgSiO3(s)

AMPHOTERICSUBSTANCESSomesubstances,suchastheHCO3

−ion,theHSO4−ion,theH2Omolecule,and

theNH3molecule, can act as either proton donors (acids) or proton receivers

(bases), depending uponwhich other substances they come into contact with.These substances are said to be amphoteric. Amphoteric substances donateprotons in the presence of strong bases and accept protons in the presence ofstrongacids.Examplesarethereactionsofthebisulfateion,HSO4

−:Withastrongacid,HSO4

−acceptsaproton:

HSO4−(aq)+H+(aq)→H2SO4(aq)

Withastrongacid,HSO4−donatesaproton:

HSO4−(aq)+OH−(aq)→H2O( )+SO4

2−(aq)

ACIDRAIN—ANENVIRONMENTALCONCERNAcid rain is currentlya subjectofgreat concern inmanycountries around theworldbecauseofthewidespreadenvironmentaldamageitreportedlycauses.Itforms when the oxides of sulfur and nitrogen combine with atmosphericmoisture toyieldsulfuricandnitricacids—bothknowntobehighlycorrosive,especiallytometals.Onceformedintheatmosphere,theseacidscanbecarriedlongdistances from their sourcebeforebeingdepositedby rain.Thepollutionmayalsotaketheformofsnoworfogorbeprecipitatedindryform.Thisdryformisjustasdamagingtotheenvironmentastheliquidform.

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Acid rain is the result of theformationofsulfuricacidfromsulfuroxides reacting with water. Nitrogenoxidesarealsoinvolved.

Theproblemofacidraincanbetracedbacktothebeginningoftheindustrialrevolution,andithasbeengrowingeversince.Theterm“acidrain”hasbeeninuseformorethanacenturyandisderivedfromatmosphericstudiesmadeintheregionofManchester,England.

In1988,aspartof theLong-RangeTransboundaryAirPollutionAgreementsponsored by the United Nations and the United States, along with 24 othercountries,aprotocolfreezingtherateofnitrogenoxideemissionsat1987levelswas ratified.The1990amendments to theCleanAirActof1967put inplaceregulations to reduce the release of sulfur dioxide from power plants to 10million tons per year by 2000. That achieved a 20 percent decrease in sulfurdioxide. The attempts continue through international organizations to furthercleantheair.These equations show the most common reactions of sulfur- and nitrogen

containinggaseswithrainwater.Thesulfurdioxidereactswithrainwatertoformsulfuricacidsolutions:

2SO2(g)+O2(g)→2SO3(g)SO3(g)+H2O( )→H2SO4(aq)

Theoxidesofnitrogenreacttoformnitrousandnitricacid:

2NO2(g)+H2O( )→HNO2(aq)+HNO3(aq)

ChapterSummaryThefollowingtermssummarizealltheconceptsandideasthatwereintroducedinthischapter.Youshouldbeabletoexplaintheirmeaningandhowyouwouldusetheminchemistry.Theyappearinboldfacetypeinthischaptertodrawyourattentiontothem.Theboldfacetypealsomakesiteasierforyoutolookthemupif you need to. You could also use the search or “Google” action on yourcomputer to get a quick and expanded explanation of these terms, laws, andformulas.

acid conjugatebase neutralizationamphoteric endpoint pHbase equivalencepoint saltbuffersolution indicator titrationconjugateacid litmus volumetricanalysisArrheniusTheory Brønsted-LowryTheory LewisTheory

InternetResourcesOnline content that reinforcesmajor concepts discussed in this chapter canbefound at the following Internet addresses if they are still available.Somemayhavebeenchangedordeleted.AcidsandBaseshttp://chemed.chem.purdue.edu/genchem/topicreview/bp/ch11/acidbase.phpThis site summarizes the important ways in which acids and bases can bedefined.Theroleofwaterisalsodescribedintheacid/baseprocess.TitrationExperimentsandMorehttp://chemistry.about.com/od/workedchemistryproblems/a/titrationexampl.htmThissitehasastep-by-stepexplanationabouthowtosolveatitrationproblem.Italsohaslinkstootherinformativesites.AcidRainhttp://www.epa.gov/acidrain/index.htmlThis Environmental Protection Agency site offers a wealth of informationconcerningthemajorenvironmentalproblemcalledacidrain.

PracticeExercises1.ThedifferencebetweenHClandHC2H3O2asacidsis

(A)thefirsthaslesshydrogeninsolution(B)thesecondhasmoreionizedhydrogen(C)thefirstishighlyionized(D)thesecondishighlyionized

2.Thehydroniumionisrepresentedas

(A)H2O+

(B)H3O+

(C)HOH+

(D)H−

3.H2SO4isastrongacidbecauseitis

(A)slightlyionized(B)unstable(C)anorganiccompound(D)highlyionized

4.Thecommonionicreactionofanacidwithabaseinvolvesionsof

(A)hydrogenandhydroxide(B)sodiumandchloride(C)hydrogenandhydronium(D)hydroxideandnitrate

5.WhichpHisanacidsolution?

(A)3(B)7(C)9(D)10

6.ThepHofasolutionwithahydrogenionconcentrationof1×10−3is

(A)+3(B)-3(C)±3(D)1+3

7.AccordingtotheBrønsted-LowryTheory,anacidis

(A)aprotondonor(B)aprotonacceptor(C)anelectrondonor(D)anelectronacceptor

8.Abuffersolution

(A)changespHrapidlywiththeadditionofanacid(B)doesnotchangepHatall(C)resistschangesinpH(D)changespHonlywiththeadditionofastrongbase

9.Thepointatwhichatitrationiscompleteiscalledthe

(A)endpoint(B)equilibriumpoint(C)calibratedpoint(D)chemicalpoint

10.If10.mLof1MHClwasrequiredtotitratea20.mLNaOHsolutionofunknownconcentrationtoitsendpoint,whatwastheconcentrationoftheNaOH?

(A)0.5M(B)1.5M(C)2M(D)2.5M

AnswersandExplanations1.(C)ThestrengthofanArrheniusacidisdeterminedbythedegreeofionizationofthehydrogensintheformula.TheHClionizestoagreatdegreeandisconsideredastrongacid,whereasHC2H3O2,aceticacid,whichisfoundinvinegar,ionizesonlytoasmalldegreeandisconsideredaweakacid.

2.(B)ThehydroniumioniswrittenasH3O+.

3.(D)H2SO4isastrongacidbecauseitishighlyionized.

4.(A)ThebasicreactionbetweenanacidandabaseisH+(aq)+OH−(aq)→H2O( )orH3O+(aq)+OH−(aq)→2H2O( )

5.(A)ThepHscaleis0to14;thenumbersbelow7areacidandthoseabove7areincreasinglybasic.

6.(A)BecausethepHisdefinedasthenegativeofthelogoftheH+

concentration,itis-(logof10−3),whichis-(-3)or+3.

7.(A)Bydefinition,aBrønsted-Lowryacidisaprotondonor.

8.(C)AbuffersolutionresiststhechangesinpH.

9.(A)Thepointinatitrationwhenthe“unknown”solutionhasbeenneutralized—inthecaseofanacid/basetitration—bythe“standard”solutionofknownconcentrationiscalledtheendpointorequivalencepoint.

10.(A)UsetheequationMacid×V2=Mbase×VbaseandchangemLtoLbydividingby1,000mL/Ltochange10.mLinto.01Land20.mLinto.02L.Thensubstituting,youget1Macid×.01Lacid=xMbase×.02Lbase.Solvingforx,yougetx=0.5Mbase.

CHAPTER12

Oxidation-ReductionandElectrochemistry

TheseskillsareusuallytestedontheSATSubjectTestinChemistry.Youshouldbeableto…•Explainthereactionsinavoltaiccell.•Useelectrodepotentialstodetermineifareactionwilloccur.•Describeelectroplatingandhowtodeterminethequantityofproductplated.•Explainthedifferencesbetweenvoltaicandelectrolyticcells.•Explainhowordinarybatterieswork.•Balanceredoxequationsusingoxidationnumbers.This chapter will review and strengthen these skills. Be sure to do thePracticeExercisesattheendofthechapter.

In theearly1830s,MichaelFaradaydiscovered thatwater solutionsof certainsubstancesconductanelectriccurrent.Hecalled thesesubstanceselectrolytes.Our definition todayof an electrolyte ismuch the same. It is a substance thatdissolvesinwatertoformasolutionthatwillconductanelectriccurrent.Theusualapparatustotestforthisconductivityisalightbulbplacedinseries

withtwoprongsthatareimmersedinthesolutiontested,asshowninFigure35.

Figure35.TestforConductivityofElectrolytes

Usingthistypeofapparatus,wecanclassifysolutionsasgood,moderate,orpoorelectrolytes.Iftheydonotconductatall, theyarecallednonelectrolytes.

Thetablebelowgivestheclassificationsofsomecommonsubstances.

Thereasonthatthesesubstancesconductwithvaryingdegreesofefficiencyisrelatedtothenumberofionsinsolution.Theioniclatticesubstanceslikesodiumchloridearedissociatedbythewater

molecules so that the individual positive and negative ions are dispersedthroughoutthesolution.Inthecaseofacovalentbondedsubstancethedegreeofpolaritydeterminestheextenttowhichitwillbeionized.Thewatermolecules,which are polar themselves, can help weaken and finally break the polarcovalentbondsbyclusteringaroundthesubstance.Whentheionsareformedinthismanner,theprocessiscalledionization;whentheioniclatticecomesapart,the process is dissociation. Substances that are nonelectrolytes are usuallybondedso that themolecule isanonpolarmolecule.Thepolarwatermoleculecannotorientitselfaroundthemoleculeandcauseitsionization.LetusseehowthecurrentwascarriedthroughtheapparatusinFigure35.The

electricitycausesoneelectrodetobecomepositivelychargedandonenegativelycharged.Ifthesolutioncontainsions,theywillbeattractedtotheelectrodewiththechargeoppositetotheirown.Thismeansthatthepositiveionsmigratetothenegative pole, and they are referred to as cations. The negative ions migratetowardthepositivepole,andtheyarecalledanions.Whentheseionsarriveatthe respective electrodes, the negative ions give up electrons and the positiveionsacceptelectrons,andwehaveacompletedpathfortheelectriccurrent.Themorehighly ionized thesubstance, themorecurrent flowsand thebrighter thelightbulbglows.ItwastheSwedishchemistArrheniuswhoproposedatheorytoexplainthebehaviorofelectrolytesinaqueoussolutions.

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REMEMBER Cations arepositively charged ions.Anions are

negativelychargedions.

OXIDATION-REDUCTIONANDELECTROCHEMISTRYThe branch of chemistry that deals with electricity-related applications ofoxidation-reduction reactions is calledelectrochemistry.Oxidation-reductionreactions involve a transfer of electrons from the substance oxidized to thesubstancereduced.Ifthetwosubstancesareincontactwitheachother,atransferofheatenergyaccompaniestheelectrontransfer.Thiscanbeshownwhenazincstripisincontactwithacopper(II)sulfatesolutioninabeaker,asshownintheaccompanyingdiagram.Thezinc strip loseselectrons to thecopper(II) ions insolution. The copper(II) ions accept the electrons and fall out of solution ascopper atoms.As electrons are transferred between zinc atoms and copper(II)ions,energyisreleasedintheformofheat,asindicatedbyariseintemperature.

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REMEMBER “Leo the lion saysGer”standsforLossofElectronsisOxidation andGainofElectrons isReduction

VoltaicCells(orGalvanicCells)In another example of an oxidation-reduction reaction, the substance that is

oxidized during the reaction is separated from the substance that is reducedduring the reaction. The electron transfer is accompanied by a transfer ofelectrical energy instead of heat. One means of separating oxidation andreductionhalf-reactionsiswithaporousbarrier,whichpreventsthemetalatomsofonehalf-reactionfrommixingwiththeionsoftheotherhalf-reaction.Ionsinthetwosolutions,however,canmovethroughtheporousbarrier.Electronscanbe transferred fromone side to theother throughan external connectingwire.Electric current moves in a closed loop path, or circuit, so this movement ofelectronsthroughthewireisbalancedbythemovementofionsinthesolution,asshowninthefigurebelow.

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REMEMBER: “An Ox (anode isoxidation) and a Red Cat”(reductionatcathode)

The zinc strip is in an aqueous solution of ZnSO4; the copper strip, in anaqueous solution of CuSO4. Both solutions conduct electricity, so they areclassifiedaselectrolytes.Anelectrodeisaconductorusedtoestablishelectricalcontactwithanonmetallicpartofacircuit,suchasanelectrolyte.Inthefigure,zincandcopperareelectrodes.Asingleelectrodeimmersedinasolutionofitsions isahalf-cell.Thezincstrip inaqueousZnSO4 isananode, theelectrode

where oxidation takes place. The copper strip in CuSO4 is a cathode, theelectrode where reduction takes place. The copper half-cell can be written asCu2+/Cu,andthezinchalf-cellasZn2+/Zn.Noticethattheelectrodeisidentifiedas the anode if it is the electrode at which oxidation takes place and as thecathode if it is thesiteatwhich reduction takesplace.Both theanodeand thecathodemaybethepositiveorthenegativeelectrodeofacell.Thesetermsarenot interchangeable. The determining factor in the identification is whetheroxidationorreductionisoccurringatthesite.The two half-cells together constitute an electrochemical cell. An

electrochemicalcell is a systemof electrodes and electrolytes inwhich eitherchemical reactions produce electrical energy or an electric current produceschemicalchange.Anelectrochemicalcellmayberepresentedbythefollowingnotation:cathode|anode.Forexample,thecellmadeupofzincandcoppercanbewrittenasCu|Zn.Therearetwotypesofelectrochemicalcells:voltaic(alsocalledgalvanic)andelectrolytic.Iftheredoxreactioninanelectrochemicalcelloccursnaturallyandproduces

electrical energy as is shown in the drawing immediately above, the cell is avoltaiccellorgalvaniccell.Cationsinthesolutionarereducedwhentheygainelectronsatthesurfaceofthecathodetobecomemetalatoms.Thishalf-reactionforthevoltaiccellshowninthedrawingisasfollows:

Cu2+(aq)+2e−→Cu(s)

Thehalf-reactionoccurringatthenegativeelectrodeoranodeis:

Zn(s)→Zn2+(aq)+2e−

Electronsgivenupat theanodepassalong theexternalconnectingwire to thecathode.Themovementofelectronsthroughthewiremustbebalancedbyamovement

ofionsinthesolution.Anionsmovetowardtheanodetoreplacethenegativelycharged electrons that aremoving away. Cationsmove toward the cathode aspositive charge is lost through reduction. Thus, sulfate ions in the CuSO4solution canmove through the barrier into the ZnSO4 solution. Likewise, theZn2+ ionspassthroughthebarrierintotheCuSO4solution.Thisporousbarriercanbereplacedbya“saltbridge”asshowninFigure44.It is important to note that if a battery is connected so that the positive

terminalcontactsthecopperelectrodeandthenegativeterminalcontactsthezincelectrode,theelectronsflowintheoppositedirection.Thebatteryforcesthecellto reverse its reaction; thezincelectrodebecomes thecathode, and thecopperelectrode becomes the anode. The half-reaction at the anode, inwhich coppermetalisoxidized,canbewrittenasfollows:

Thereductionhalf-reactionofzincatthecathodeiswrittenasfollows:

ElectrodePotentialsInthediscussionofacidsandmetalsreactingtoproducehydrogen,theactivitiesofmetalscomparedwiththeactivityofhydrogenareshown.Amoreinclusivepresentationofthisactivityofmetals,calledtheelectromotiveseries,isshowninTable10.From this chart you notice that zinc is above copper and, therefore, more

active.Thismeanszinccandisplacecopperionsinasolutionofcoppersulfate:

Zn0(s)+Cu2+(aq)+SO42−(aq)→Cu0(s)+Zn2+(aq)+SO4

2−(aq)

Thezincatommusthavelost2electronstobecomeZn2+ions:

Zn0(s)→Zn2+(aq)+2e−(electrons)

At the same time, the Cu2+ must have gained 2 electrons to become the Cu0atom:

Cu2+(aq)+2e−(electrons)→Cu0(s)

These two equations are calledhalf-reactions. The loss of electrons by thezinciscalledoxidation;thegainofelectronsbythecopperion,reduction.Itisimportant to remember that the gain of electrons is reductionand the loss of

electronsisoxidation.Awaytoremember this is thestatement“LEOthe lionsaysGER.”LEOtranslatesinto“LossofElectronsisOxidation,”andGERinto“Gain of Electrons is Reduction.” The fact that the zinc in this reaction isoxidizedbygivingupelectronsmakesitpossibleforelectronstobegainedbythecopper,whichisactingasareducingagent.Similarly,becausethecopperinthisreactionisbeingreducedbygainingelectrons,electronscanbelostbythezinc,whichisactingasanoxidizingagent.

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REMEMBER The reducing agentis oxidized. The oxidizing agent isreduced.

Themetal elements that lose electrons easily and become positive ions areplacedhigh in the electromotive series.Themetal elements that lose electronswithmoredifficultyareplacedlowerinTable10.Theenergyrequiredtoremoveelectronsfrommetallicatomscanbeassigned

numericalvaluescalledelectrodepotentials.Theenergies,E0,requiredforthereductionofcommonelementsareshowninTables10and11.

*Ameasureinvoltsofthetendencyofatomstogainorloseelectrons.

These voltages depend on the nature of the reaction, the concentrations ofreactantsandproducts,andthetemperature.Throughoutthisdiscussion,weusestandardconcentrations,thatis,allionsormoleculesinaqueoussolutionareataconcentrationof1molar.Furthermore,allgasestakingpartinthereactionsareat 1 atmosphere pressure, and the temperature is 25°C. The voltagemeasuredundertheseconditionsiscalledstandardvoltage.Thecurrentlyacceptedconventionistogivethepotentialsofhalf-reactionsas

reductionprocesses.Forexample:

2H+(aq)+2e−→H2(g)

The E0 values corresponding to these half-reactions are called standard

reductionpotentials.

TIP

If theE0cell is positive, the reactionwilloccur.

SomereductionelectrodepotentialsareshowninthelastcolumnofTables10and11.Noticethathydrogenisusedasthestandardwithanelectrodepotentialof zero. These values help you to predict what reactions will occur and howreadilytheywilloccur.

Thefollowingexampleswillclarifytheuseofelectrodepotentials.Ifmagnesiumreactswithchlorine,wecanwritetheequation

Mg(s)+Cl2(g)→MgCl2(s)

Thetwohalf-reactionswiththeelectrodepotentialsare:

In thenet reaction,E0 is a positive number.This indicates that the reactionoccursspontaneously.

TIP

REMEMBERWhen theE0cell is apositive value, the reaction willoccurspontaneously.

You should also note that the total number of electrons lost in oxidation isequaltothetotalnumberofelectronsgainedsothatthenetreaction(arrivedatbyaddingthetworeactions)doesnotcontainanyelectrons.Forsodiumreactingwithchlorinetheequationis:

2Na(s)+Cl2(g)→2NaCl(s)

Thetwohalf-reactionsare:

TIP

Thisnoteisimportant.

Again,theE0forthisreactionispositiveandthereactionisspontaneous.ThenextexampleshowsanegativeE0.Coppermetalplacedinanacidsolutionisshownasfollows:

SinceE0isnegative,weknowthereactionwillnottakeplace.ManytimesthereductionreactionswiththeirE0valuesareshownformetals.

Ifyoumustuse theoxidation reactionsof thesemetals, theequationsmustbereversed,and the signofE0 changed.For example,when apieceof copper isplacedintoasolutionofsilverions:

ThisreactionwilloccurspontaneouslysinceE0ispositive.

•SAMPLEPROBLEM:

Calculatethecellvoltageofthefollowingreaction:

Zn(s)|Zn2+(0.001M)||Ag+(0.1M)|Ag(s)

(Eachsideofthe||representsthehalf-reactioncharacters,withtheconcentrationwhenappropriate.)Thereactionsare:Thismethodisbasedonbalancingtheelectronsgainedandtheelectronslost

inthetwohalf-reactions.Sincethecellvoltageispositive,thereactionwilloccur.

ElectrolyticCellsInthesecondtypeofelectrochemicalreactions,theredoxreactionsdonotoccurspontaneously but can be forced to take place by supplying energy with anexternal current. These reactions are called electrolytic reactions. Someexamplesofthistypeofreactionareelectroplating,electrolysisofsaltsolution,electrolysis of water, and electrolysis of molten salts. An example of theelectrolyticsetupisshowninFigure36.

Figure36.ElectrochemicalReactions

If this solution contained Cu2+ cations and Cl− anions, the half-reactionswouldbe:

Notice that theE0 for this reaction isnegative, soanoutside sourceof energymustbeusedtomakeitoccur.Inelectroplating,whereelectrolysisisusedtocoatamaterialwithalayerof

metal, theobject tobeplated ismade thecathode in thereaction.Abarof theplatingmetal ismade the anode, and the solution contains ions of the platingmetal.SeeFigure37below.

Figure37.ElectroplatingaMetalFork

In this example, silver nitrate, AgNO3, can be used to silver plate. Whendissolved in H2O, it forms a solution containing silver ions, Ag+. Assume ametalforkismadethecathodeandabarofsilverismadetheanode.Whenthecurrentisswitchedon,thepositivesilverionsinthesolutionareattractedtothefork.Whenthesilverionsmakecontact,theyarereducedandchangefromionstoatomsofsilver.Theseatomsgraduallyformametalliccoatingonthefork.Atthe anode, oxidation occurs, and the anode itself is oxidized. These two halfreactionsare:

Cathodereaction:Ag+(aq)+e−→Ag(s)Anodereaction:Ag(s)→Ag+(aq)+e−

The silver ions formed at the anode replace those in the solution that areplatedontotheforkduringthecathodereaction.Another example is the electrolysis of awater solution of sodium chloride.

Thiswatersolutioncontainschlorideions,whichareattractedtotheanodeandset free as chlorine molecules. The cathode reaction is somewhat morecomplicated.Althoughthesodiumionsareattractedtothecathode,theyarenotset free as atoms. Remember that water can ionize to some extent, and theelectromotiveseriesshowsthatthehydrogenionisreducedmoreeasilythanthesodium ion. Therefore, hydrogen, not sodium, is set free at the cathode. Thereactioncanbesummarizedinthisway:

Another example of electrolysis is the decomposition of water by using anapparatusliketheoneshowninFigure38.Thesolutioninthisapparatuscontainsdistilledwaterandasmallamountof

H2SO4. The reason for adding H2SO4 is to make the solution an electrolytebecausedistilledwateralonewillnotconductanelectriccurrent.Thesolution,therefore,containsionsofH+,HSO4

−,andSO42−.

Figure38.SetupfortheElectrolysisofWater

The hydrogen ions (H+) migrate to the cathode where they are reduced tohydrogen atoms and formhydrogenmolecules (H2) in the formof a gas. TheSO4

2−andHSO4−migratetotheanodebutarenotoxidizedsincetheoxidation

of water occursmore readily. These ions then aremerely spectator ions. Theoxidizedwaterreactsasshowninthefollowinghalf-reaction.

Notice that the equation shows 2 volumes of hydrogen gas are releasedwhileonly1volumeofoxygengasisliberated.ThisagreeswiththediscussionofthecompositionofwaterinChapter7.There are two important differences between the voltaic cell and the

electrolyticcell:

1.Theanodeandcathodeofanelectrolyticcellareconnectedtoabatteryorotherdirect-currentsource,whereasavoltaiccellservesasasourceofelectricalenergy.

2.Inelectrolyticcells,electricalenergyfromanexternalsourcecausesnonspontaneousredoxreactionstooccur.Involtaiccells,however,spontaneousredoxreactionsproduceelectricity.Thus,inanelectrolyticcell,electricalenergyisconvertedintochemicalenergy;inavoltaiccell,

chemicalenergyisconvertedintoelectricalenergy.

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Know the differences between thevoltaiccellandtheelectrolyticcell.

ApplicationsofElectrochemicalCells(CommercialVoltaicCells)One of the most common voltaic cells is the ordinary “dry cell” used inflashlights. Its makeup is shown in the drawing below, along with anode,cathode,andpastereactions.

Theautomobileleadstoragebatteryisalsoavoltaiccell.Whenitdischarges,thereactionsareasshowninthedrawingbelow.

QUANTITATIVEASPECTSOFELECTROLYSIS

RelationshipBetweenQuantityofElectricityandAmountofProductsThe amounts of products liberated at the electrodes of an electrolytic cell arerelated to the quantity of electricity passed through the cell and the electrodereactions.Inelectrolysis,1moleofelectrons iscalled1faradayofelectriccharge. In

theelectrolysisofmoltenNaCl,1faradaywillliberate1moleofsodiumatoms.

Cathodereaction:Na+(aq)+e−→Na(s)

Atthesametime,1moleofCl−ionsattheanodewillform1moleofchlorineatomsandthus0.5moleofchlorinemolecules.If themetallic ionhadbeenCa2+, 1 faradaywould releaseonly0.5moleof

calciumatomssinceeachcalciumionrequires2electrons,asshownhere:

Ca2+(aq)+2e−→Ca(s)

SAMPLEPROBLEM:Howmanymolesofelectronsarerequiredtoreduce2.93gramsofnickelionsfrommeltedNiCl2?

TIP

Use the equation to determine thequantityofelectronsneeded.

Thereactionis

Ni2+(aq)+2e−→Ni(s)

The2.93grepresents

Since2molofelectronsareneededtoproduce1molofNi(s),

0.1molofelectrons

BALANCINGREDOXEQUATIONSIngeneral,manychemicalreactionsaresimpleenoughthatoncetheirreactantsandproducts areknown, theequationscanbe readilywrittenandbalancedbyinspection.Someredoxreactions,however,areofsuchcomplexitythatwritingthemrequiresseveralsteps.Firstlimitthechangeinvolvedtotheactualelectronshiftsthatoccur.Balancethenumberofelectronsgainedandlost.Therestofthebalancingcanthenusuallybedonewithouttoomuchdifficulty.Severalmethodscan be used to accomplish this. We will show two methods with severalexamplesofeach.Thefirstistheelectronshiftmethod.Thesecondistheion-electron method. Since both methods assign oxidation states to the elementsinvolved,sotheassigningofvaluesisbrieflyreviewedhere.

TheRulesforAssigninganOxidationStateToapplytheserules,rememberthatthesumof theoxidationstatesmustequalzeroforanelectricallyneutralcompound.Foranion, thesumoftheoxidationstatesmustequalthechargeontheion,includingpolyatomicions.

1.Theoxidationstateofanatominanelementiszero.Examples:0forNa(s),O2(g),H(l)

2.Theoxidationstateofamonoatomicionisthesameasitscharge.Examples:Na+1,Cl−1

3.Theoxidationstateoffluorineis−1initscompounds.Examples:HFwhere1H(+1)+1F(−1)=0,PF3where1P(+3)+3F(−1)=0

4.Theoxidationstateofoxygenisusually−2initscompounds.Example:H2Owhere2H(+1)+1O(−2)=0Oneexceptiontothisruleoccurswhenoxygenisbondedtofluorineandtheoxidationstateoffluorinetakesprecedence.Anotherexceptionoccurs

inperoxidecompounds,wheretheoxidationstateisassignedthevalueof−1.

5.Theoxidationstateofhydrogeninmostcompoundsis+1.Examples:H2O,HCl,NH3Inhydrides,thereisanexception.Oxygenisassignedthevalueof−1.

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Notice that electrons gained are ontheleftsideandelectronslostareontherightside.

TheElectronShiftMethodThe oxidation state method breaks the reaction into two half-reactions, thereductionreactionandtheoxidationreaction.Thismethodisbasedonbalancingtheelectronsgainedandtheelectronslostinthetwohalf-reactions.

FIRSTEXAMPLE:BalancetheequationHCl(aq)+MnO2(s)→H2O(l)+MnCl2(aq)+Cl2(g)

1.Theoxidationstatesarewrittenabovealltheelementsintheequation.

2.Theoxidationstateofthemanganesehaschangedfrom+4to+2,whiletheoxidationstateofthechlorinethatemergesasagashaschangedfrom−1to0.Achangefrom+4to+2isareductionintheoxidationstateandagaininelectrons.Achangefrom−1to0isagainintheoxidationstateandalossofelectrons.Thesearewrittenasthehalf-reactionsoftheionsinvolvedwiththeelectronchanges.Noticethatoxidationstateshavethe+or−ontheleftofthenumberandthationicchargesareshownontherightofthenumber.Mn4+(aq)+2e−→Mn2+(aq)Reductionreaction

Cl1−(aq)→Cl(g)+1e−Oxidationreaction

3.Thenextstepistoassurethatthenumberofatomsrequiredbytheformulasinthereactantsequalsthenumberofatomsintheproducts.NoticethattheproductCl2intheoriginalequationisadiatomicmoleculeandrequires2atomsinthemolecularformula.Thismeanstheremustbe2Cl−ionsprovidedontheleftsideofthe

equation.Atotalof2e−arelost,oneforeachCl−.Mn4+(aq)+2e−→Mn2+(aq)Reductionreaction2Cl−(aq)→Cl2(q)+2e−Oxidationreaction

4.Ifthenumberofelectronsgainedinreductiondidnotequalthenumberofelectronslostinoxidation,wewouldhavehadtomultiplyeitheronereactionlineorbothbyanappropriatenumbertoassurethatthenumberofelectronslostequaledthenumberofelectronsgained.Thiswillbeshowninthenextexample.

5.Nextaddthetwohalf-reactions.

7.Fromthenumbersthusestablished,theremainingcoefficientscanbededucedbyinspection.Noticethat2moremoleculesofHClarerequiredtofurnishthechlorinefortheMnCl2,andthe2atomsofoxygeninMnO2form2H2O.

8.Thefinalbalancedequationis

4HCl(aq)+MnO2(s)→2H2O(l)+MnCl2(aq)+Cl2(g)

Nowconsideramorecomplicatedreaction.

SECONDEXAMPLE:Balancetheequation

HCl(aq)+KMnO4(aq)→H2O(l)+KCl(aq)+MnCl2(aq)+Cl2(g)

1.Theoxidationstatesarewrittenabovealltheelementsintheequation

2.Inspectionofoxidationstatesshowsthattheoxidationstateofthemanganesehaschangedfrom+7to+2,whiletheoxidationstateofthechlorinethatemergesasagashaschangedfrom−1to0.Achangefrom+7to+2isareductionintheoxidationstateandagaininelectrons.Achangefrom−1to0isagainintheoxidationstateandalossofelectrons.Thesearewrittenasthehalf-reactionsoftheionsinvolvedwiththeelectronchanges.Noticethatoxidationstateshavethe+or−ontheleftofthenumberandthationicchargesareshownontherightofthenumber.Mn7+(aq)+5e−→Mn2+(aq)ReductionreactionCl−(aq)→Cl+1e−Oxidationreaction

3.Thenextstepistoassurethatthenumberofatomsrequiredbytheformulasinthereactantsequalsthenumberofatomsintheproducts.Notice,hereagain,thattheproductCl2intheoriginalequationisadiatomicmoleculeandrequires2atomsinthemolecularformula,sotheoxidationreactionmusthavethediatomicmoleculeCl2.Thisisdonebymultiplyingtheothermembersoftheoxidationreactionby2toprovidethe2Cl1−fortheCl2.Mn7+(aq)+5e−→Mn2+(aq)Reductionreaction2Cl−(aq)→Cl2(q)+2e−Oxidationreaction

4.Rememberthatthenumberofelectronsgainedinreductionmustequalthenumberelectronslostintheoxidationreaction.Inthisreaction,wehavetomultiplythereductionreactionby2andtheoxidationreactionby5sothatthenumberofelectronslostequalthenumberofelectronsgained.2Mn7+(aq)+10e−→2Mn2+(aq)Reductionreaction10Cl−1(aq)→5Cl2(q)+10e−Oxidationreaction

5.Nextaddthetwohalf-reactions.

Atthispoint,inspectionshowsthattheproducts2KCl(aq)+2MnCl2(aq)+5Cl2(g)needatotalof16Cltobeprovidedinthereactants.TheonlysourceofClinthereactantsisHCl(aq).Therefore,thecoefficientofHClmustbe16.

TheIon-ElectronMethodThesecondmethodismorecomplexbutseemstorepresentthetruemechanismofsuchreactionsmoreclosely.In this method, only units that actually have individual existence (atoms,

molecules, or ions) in the particular reaction being studied are taken intoconsideration.Theprincipaloxidizingagentandtheprincipalreducingagentarechosenfromthese(byamethodtobeindicatedlater).Thentheelectronlossorgain of each of these two principal actors is determined by taking intoconsiderationthefactthat,sinceelectronscanneitherbecreatednordestroyed,electrons lost by one of these actors must be gained by the other. This isaccomplishedbyusing twoseparatepartial equations representing thechangesundergonebyeachofthetwoprincipalactors.Probablythebestwaytoshowhowthemethodoperateswillbetofollowin

detailthestepstakeninbalancingtwoactualoxidation-reductionreactions.

FIRSTEXAMPLE:AssumethattheequationK2CrO4(aq)+HCl(aq)→KCl(aq)+CrCl3(aq)+H2O(l)+Cl2(g)istobebalanced.Noticethisisanacidicsolution.

1.Determinewhichofthesubstancespresentareinvolvedintheoxidation-reduction.Thisisdonebylistingallsubstancespresentoneachsideofthearrowin

theirmolecularorionicformandthencrossingoutthosethatappearonbothsidesofthearrowwithoutbeingchangedinanyway.

NotethatCl−isnotcrossedoutalthoughitappearsonbothsidesbecausesomeoftheCl−fromtheleftsideappearsinachangedform,namely,Cl2,ontheright.

Thetwosubstancesontheleftsidethatarenotcrossedoutaretheonesinvolvedintheoxidation-reduction.

If,asinthiscase,therearemorethantwo,disregardH+,OH−,orH2O;thiswillleavethetwoprincipalactors.

2.Indicateintwoasyetunbalancedpartialequationsthefateofeachofthetwoactiveagentsthus:

CrO42−(aq)→Cr3+(aq)

Cl−(aq)→Cl2(g)

3.Balancetheseequationschemically,insertinganysubstancenecessary.

CrO42−(aq)+8H+(aq)→Cr3+(aq)+4H2O(l)

2Cl−(aq)→Cl2(g)Intheupperpartialequation,8H+hadtobeaddedinordertocombine

withtheoxygenfromtheCrO42−ion.

H+alwaysisusedforthispurposeinacidsolutions.Thenextexamplehandlesabasicsolutionproblem.

4.Balancetheseequationselectricallybyaddingelectronsoneithersidesothatthetotalelectricchargeisthesameontheleftandrightsides,thus:

CrO42−(aq)+8H+(aq)+3e–→Cr3+(aq)+4H2O(l)

2Cl−(aq)→Cl2(g)+2e−

5.Addthesepartialequations.Butbeforeweaddwemustrealizethatelectronscanneitherbecreated

nordestroyed.Electronsaregainedinoneoftheseequationsandlostintheother.THOSEGAINEDINTHEONEMUSTCOMEFROMTHEOTHER.Thereforewemustmultiplyeachoftheseequationsthroughbynumberssochosenthatthenumberofelectronsgainedinoneequationwillbethesameasthenumberlostintheother,thus:

2[CrO42−(aq)+8H+(aq)+3e−→Cr3+(aq)+4H2O(l)]

3[2Cl−(aq)→Cl2(g)+2e−]

THISISTHEKEYTOTHEMETHOD!

Addingthemultipliedequations,weget:

SECONDEXAMPLE:(Inabasicsolution)

Notethat,becausethisreactiontakesplaceinabasicsolution,H2Owasusedtoremoveoxygenintheupperpartial.

NotealsothatinthesecondpartialitwasnecessarytoADDoxygenandthatthiswasdonebymeansofOH−ion.

Ifthesolutionhadbeenacid,thenH2Owouldhavebeenusedforthispurpose,thus:

I−(aq)+3H2O(l)→IO3−(aq)+6H+(aq)+6e−

TIP

REMEMBERIngeneral,youwillmeet three typesofpartialequations:

1.Whereelectronsonlyareneededtobalance,asinthesecondpartialofthefirstexampleabove.

2.Whereoxygenmustberemovedfromanion.

Inacidsolution,H+isusedforthispurposeasinthefirstpartialofthefirstexampleabove.

Inbasicsolution,H2Oisusedforthisasinthefirstpartialofthe

secondexampleabove.

3.Whereoxygenmustbeaddedtoanion.

Inbasicsolution,OH−isusedforthispurposeasinthesecondpartialofthesecondexampleabove.

Inacidsolution,H2Oisusedforthisasin:

SO32−(aq)+H2O(l)→SO4

2−(aq)+2H+(aq)+2e−

TIP

Thisoneisachallenge!

TRYTHESEPROBLEMS:

1.Zn(s)+HNO3(aq)→Zn(NO3)2(aq)+NH4NO3(aq)+H2O(l)Ans.4,10,4,1,3

2.Cu(s)+HNO3(aq)→Cu(NO3)2(aq)H2O(l)+NO(g)Ans.3,8,3,4,2

3.KMnO4(aq)+HCl(aq)→KCl(aq)+MnCl2(aq)+H2O(l)+Cl2(g)Ans.2,16,2,2,8,5

ANSWERS

1.Thehalf-reactionsbalancedchemically.(Noticethisisinanacidicsolution.)

Zn→Zn2+

NO3−+10H+→NH4

++3H2O

Balancingelectricallyandadding:

Intheequation:

4Zn(s)+10HNO3(aq)→4Zn(NO3)2(aq)+NH4NO3(aq)+3H2O(l)

2.Thehalf-reactionsbalancedchemically.(Noticethisisinanacidicsolution.)

Cu0→Cu2+

NO31−+4H+→NO+2H2O

Balancingelectricallyandadding:

Intheequation:

3Cu(s)+8HNO3(aq)→3Cu(NO3)2(aq)+4H2O(l)+2NO(g)

3.Thehalf-reactionsbalancedchemically.(Noticethisisinanacidicsolution.)

MnO4−+8H+→Mn2++4H2O

2Cl−→Cl2

Balancingelectricallyandadding:

Intheequation:

ChapterSummaryThefollowingtermssummarizealltheconceptsandideasthatwereintroducedinthischapter.Youshouldbeabletoexplaintheirmeaningandhowyouwouldusetheminchemistry.Theyappearinboldfacetypeinthischaptertodrawyourattentiontothem.Theboldfacetypealsomakesiteasierforyoutolookthemupif you need to. You could also use the search or “Google” action on yourcomputer to get a quick and expanded explanation of these terms, laws, andformulas.

anions electrolyte oxidationanode electrolyticreaction oxidizingagentcathode electromotiveseries potentialcations electroplating reducingagentdissociation faraday reductionelectrochemicalcell galvaniccell standardvoltageelectrode half-cellelectrolysis voltaiccell

electrodepotential ionizationelectrolysis nonelectrolyte

InternetResources

Online content that reinforcesmajor concepts discussed in this chapter canbefound at the following Internet addresses if they are still available.Somemayhavebeenchangedordeleted.RedoxReactionshttp://chemistry.about.com/od/generalchemistry/ss/redoxbal.htmThis site offers a tutorial onoxidation-reduction reactions. It shows a step-by-stepsolutiontobalancingaredoxreaction.VoltaicCellshttp://chemwiki.ucdavis.edu/Analytical_Chemistry/Electrochemistry/Voltaic_CellsThis site offers an animated simulation of a voltaic cell with a completeexplanationofhowthevoltaiccellfunctions.

PracticeExercises1.Whichofthefollowingwhendissolvedinwaterandplacedintheconductivityapparatuswouldcausethelighttoglow?

(A)tablesalt(B)ethylalcohol(C)sugar(D)glycerine

2.Inquestion1,thereasonthatacurrentcouldflowisthat

(A)ionscombinetoformmolecules(B)moleculesmigratetothechargeplates(C)ionsmigratetothechargeplates(D)sparkscrossthegap

3.Theextentofionizationdependsonthe

(A)natureofthesolvent(B)natureofthesolute(C)concentrationofthesolution(D)temperatureofthesolution(E)alloftheabove

4.WhichofthefollowingisTRUE?

(A)Thenumberofpositiveionsinsolutionequalsthenumberofnegativeions.

(B)Thepositiveionsarecalledanions.(C)Thepositiveionsarecalledcathodes.(D)Thetotalpositivechargeequalsthetotalnegativechargeinsolution.(E)Noneoftheabove

5.Thehydroniumionisrepresentedas

(A)H2O+

(B)H3O+

(C)HOH+

(D)H−

6.Intheelectrolysisofcopperchloride,thesubstanceliberatedattheanodeis

(A)copper(B)chlorine(C)hydrogen(D)copperchloride

7.Ionsareparticlesthatexist

(A)onlyinwatersolutions(B)insomecrystals(C)inpolarcovalentcompounds(D)incovalentcompoundsthatarenotpolar

8.Ioniccompoundswillconductanelectriccurrentwhentheyare

(A)solidified(B)melted

(C)frozen(D)dehydrated

9.Thecathodeinanelectrochemicalcellistheelectrodethatis

(A)alwaysnegative(B)alwayspositive(C)alwaysneutral(D)theelectrodeatwhichreductiontakesplace

10.Electrolysisofadilutesolutionofsodiumchlorideresultsinthecathodeproduct

(A)sodium(B)chlorine(C)hydrogen(D)oxygen

11.Electrodepotentialsare:

Zn0→Zn2++2e−E0=+0.76VAu0→Au3++3e−E0=-1.42V

If a gold foilwereplaced in a solution containing zinc ions, the reactionpotentialwouldbecalculatedtobe

(A)−1.34V(noreaction)(B)−2.18V(noreaction)(C)−0.66V(noreaction)(D)+2.18V(reaction)(E)+1.34V(reaction)

12.Apositivereactionpotentialindicatesthat

(A)thereactionwillnotoccur(B)thereactionwilloccurandgiveoffenergy(C)thereactionwilloccurifheatorenergyisadded(D)thereactionwillpoweranoutsidealternatingelectriccurrent

Questions13–15

Thefollowingelementsarelistedinorderofdecreasingreactivityastheyappearintheelectrochemicalseries.

Ca,Na,Mg,Zn,Fe,H,Cu,Hg,Ag,Au

13.Theelementthatisthebestreducingagentandtheeasiesttooxidizeis

(A)Ca(B)Au(C)H(D)Fe(E)Cu

14.Ofthefollowing,theelementthatdoesNOTreactwithhydrochloricacidtoproducehydrogengasis

(A)Zn(B)Fe(C)Hg(D)Ca(E)Mg

15.Intheelectrochemicalcellshownabove,whichofthefollowinghalf-reactionsoccursattheanode?

(A)Cu2++e−→Cu+(B)Zn(s)→Zn2++2e−

(C)Zn2++2e−→Zn(s)(D)Cu(s)→Cu2++2e−

(E)Cu2++2e−→Cu(s)

AnswersandExplanations1.(A)Tablesaltistheonlysubstancelistedthathasionswhendissolvedinitswatersolutionandwillshowacurrentismovingthroughthesystembylightingtheconductivityapparatus.

2.(C)Thecurrentiscarriedthroughthesolutionbyionsmigratingtothechargedplatesthatactastheanodeandthecathode.

3.(E)Theextentofionizationofasubstanceinsolventdependsonallfourofthelistedfactors.

4.(D)Theonlystatementthatistrueisthatthetotalpositivechargeinsolutionequalsthetotalnegativecharge.Thepositiveionsmigratetothenegativepolecalledthecathodesotheyarecalledcations.

5.(B)ThehydroniumioniswrittenasH3O+.

6.(B)Becausetheanodeispositivelycharged,itattractsthenegativelychargedCl-ionsthatarereleasedfromcopperchloride.Whenitisoxidizedbylosingitselecton,thechlorineatomthenformsaCl2moleculewithanotheratomofchlorinetobereleasedaschlorinegas.Theanodereactionwouldbe:

2Cl−(aq)→Cl2(g)+2e−

7.(B)Ionsexistnotonlyinsomewatersolutionsbutalsoinioniccrystallatticeslikesodiumchloride.

8.(B)Whenanioniccompoundismelted,theionsbecomefreetomigrateintheliquidandtherebycarryanelectriccurrent.

9.(D)Thecathodeinanelectrochemicalcellistheelectrodeatwhichreductionoccurs.Theotherpoleatwhichoxidationexistsiscalledtheanode.

10.(C)Theelectrolysisofadilutewatersolutionofsodiumchloridecontainschlorideions,whichareattractedtotheanodeandaresetfreeaschlorinemolecules.Thecathodereactionissomewhatmorecomplicated.Althoughthesodiumionsareattractedtothecathode,theyarenotsetfreeasatoms.Becausewatercanionizetosomeextentandthestandardelectrodechartshowsthatthehydrogenionisreducedmoreeasilythanthesodiumion,itishydrogen,notsodium,thatissetfreeatthecathode.Thereactionsare:

11.(B)Becausezincishigherthangoldinthestandardreductionpotentialslisting,itwillremainintheionicform,whereasgoldwillfavorthenonionizedform.Thetwohalf-reactionsthatwouldhavetooccurwiththeelectrodepotentialsforeachare:

Thisnegativecellpotentialindicatesthatthesereactionswouldnotoccur.*Note:Thestandardpotentials(E0)arenotmultipliedby thecoefficientsincalculatingtheE0forthereaction.

12.(B)Apositivereactionpotentialindicatesthatthereactionwilloccurandthatenergyisgivenoff.

13.(A)Caisthemostactive,therefore,itloseselectronssothatreductioncanoccur.Reducingagentsareoxidized.

14.(C)BecauseHgisbelowHinactivity,HgcannotdisplaceH.

15.(B)Znactsastheanodeinthissetupbecauseitishigherontheactivityseriesthancopper.

CHAPTER13

SomeRepresentativeGroupsandFamilies

TheseskillsareusuallytestedontheSATSubjectTestinChemistry.Youshouldbeableto…•Describetheproperties,bothphysicalandchemical,ofthemajormembersofeachgroupandfamily,andthecommoncompoundsformedbythesulfur,halogen,andnitrogenfamiliesandbymajormetalsandtheiralloys.

•Writeequationsformajorreactionsinvolvingtheseelements.This chapter will review and strengthen these skills. Be sure to do thePracticeExercisesattheendofthechapter.

In the following section, a brief description is givenof someof the importantand representative groups of elements usually discussed in most first-yearchemistrycourses.

SULFURFAMILYSince we discussed oxygen in Chapter 5, the most important element in thisfamilylefttodiscussissulfur.SulfurisfoundfreeinthevolcanicregionsofJapan,Mexico,andSicily.Itis

removedfromtherockmixturesbyheatinginretortsorfurnaces.

SulfuricAcidImportantpropertiesofsulfuricacid.Sulfuricacidionizesintwosteps:

H2SO4(l)+H2O(l) H3O+(aq)+HSO4−(aq)Ka1isverylarge.

HSO4−(aq)+H2O(l) H3O+(aq)+SO4

2−(aq)Ka2isverysmall.

to form a strong acid solution. The ionization is more extensive in a dilutesolution.Mosthydroniumionsareformedinthefirststep.SaltsformedwiththeHSO4−(bisulfateion)arecalledacidsalts;theSO4

2−(sulfateion)formsnormalsalts.Sulfuricacidreactslikeotheracids,asshownbelow:

Withactivemetals:Zn(s)+H2SO4(aq)→ZnSO4(aq)+H2(g)(fordiluteH2SO4)

Withbases: 2NaOH(aq)+H2SO4(aq)→Na2SO4(aq)+2H2O(l)

Withmetaloxides: MgO(s)+H2SO4(aq)→MgSO4(aq)+H2O(l)

Withcarbonates:CaCO3(s)+H2SO4(aq)→CaSO4(aq)+H2O(l)+CO2(g)

Sulfuricacidhasotherparticularcharacteristics.

Asanoxidizingagent:

Cu(s)+2H2SO4(aq)(concentrated)→CuSO4(aq)+SO2(g)+2H2O(l)

Asadehydratingagentwithcarbohydrates:

C12H22O11(sugar) 12C(s)+11H2O(l)

OtherImportantCompoundsofSulfurHydrogensulfide is a colorless gas having anodor of rotten eggs. It is fairlysoluble in water and is poisonous in rather small concentrations. It can bepreparedbyreactingferroussulfidewithanacid,suchasdiluteHCl:

FeS(s)+2HCl(aq)→FeCl2(aq)+H2S(g)

Hydrogensulfideburnsinexcessoxygentoformcompoundsofwaterandsulfurdioxide.Ifinsufficientoxygenisavailable,somefreesulfurwillform.Itisonlyaweakacidinawatersolution.Hydrogensulfideisusedwidelyinqualitativelaboratory tests since many metallic sulfides precipitate with recognizablecolors. These sulfides are sometimes used as paint pigments. Some commonsulfidesandtheircolorsare:

ZnS—WhiteCdS—BrightyellowAs2S3—LemonyellowSb2S3—OrangeCuS—BlackHgS—BlackPbS—Brown-black

Anotherimportantcompoundofsulfurissulfurdioxide.Itisacolorlessgaswithasuffocatingodor.Thestructureofsulfurdioxideisagoodexampleofresonancestructures.Its

moleculeisdepictedinFigure39.

Figure39.SulfurDioxideMolecule

YouwillnoticeinFigure39thatthecovalentbondsbetweensulfurandoxygenareshowninonedrawingassinglebondsandintheotherasdoublebonds.Thissignifies that the bonds between the sulfur and oxygens have been shown byexperimentationtobeneithersinglenordoublebonds,but“hybrids”ofthetwo.

Sulfurtrioxide,shownbelow,alsohasresonancestructures.

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Resonance is a hybrid of the twostructuresshown.

“—”indicatesacovalentbond

HALOGENFAMILYThecommonmembersofthehalogenfamilyareshowninTable13withsomeimportantfactsconcerningthem.

Because each halogen lacks one electron in its outer principal energy level,theseelementsusuallyareacceptorsofelectrons(oxidizingagents).Fluorineisthemostactivenonmetalintheperiodicchart.

SomeImportantHalidesandTheirUses—commonacidpreparedinthelaboratorybyreactingsodium

Hydrochloricacid chloridewithconcentratedsulfuricacid.Itisusedinmanyimportantindustrialprocesses.

Silverbromideandsilveriodide

—halidesusedonphotographicfilm.Lightintensityisrecordedbydevelopingasblackmetallicsilverthoseportionsofthefilmuponwhichthelightfellduringexposure.

Hydrofluoricacid —acidusedtoetchglassbyreactingwithSiO2toreleasesiliconfluoridegas.Alsousedtofrostlightbulbs.

Fluorides —usedindrinkingwaterandtoothpastetoreducetoothdecay.

NITROGENFAMILYThe most common member of this family is nitrogen itself. It is a colorless,odorless,tasteless,andratherinactivegasthatmakesupaboutfour-fifthsoftheairinouratmosphere.TheinactivityofN2gascanbeexplainedbythefactthatthe two atoms of nitrogen are bonded by three covalent bonds thatrequire a great deal of energy to break. Since nitrogenmust be “pushed” intocombining with other elements, many of its compounds tend to decomposeviolentlywithareleaseoftheenergythatwentintoformingthem.Nature“fixes”nitrogen,ormakesnitrogencombine,bymeansofanitrogen-

fixingbacteria found in the rootsofbeans,peas, clover, andother leguminousplants.Dischargesoflightningalsocausesomenitrogenfixationwithoxygentoformnitrogenoxides.

NitricAcidAnimportantcompoundofnitrogenisnitricacid.Thisacidisusefulinmakingdyes,celluloidfilm,andmanyofthelacquersoncars.Itsphysicalproperties are: it is a colorless liquid (whenpure), it isoneand

one-halftimesasdenseaswater,ithasaboilingpointof86°C,thecommercialformisabout68%pure,anditismisciblewithwaterinallproportions.Its outstanding chemical properties are: the dilute acid shows the usual

propertiesofanacidexceptthatitrarelyproduceshydrogenwhenitreactswithmetals,anditisquiteunstableanddecomposesasfollows:

4HNO3(aq)→2H2O(l)+4NO2(g)+O2(g)

Because of this ease of decomposition, nitric acid is a good oxidizing agent.When it reacts with metals, the nitrogen product formed will depend on theconditionsofthereaction,especiallytheconcentrationoftheacid,theactivityofthemetal,andthetemperature.Ifthenitricacidisconcentratedandthemetaliscopper,theprincipalreductionproductwillbenitrogendioxide(NO2),aheavy,red-browngaswithapungentodor.

Cu(s)+4HNO3(aq)→Cu(NO3)2(aq)+2NO2(g)+2H2O(l)

Withdilutenitricacid,thisreactionis:

3Cu+8HNO3→3Cu(NO3)2+4H2O+2NO(g)

TheproductNO,callednitricoxide,iscolorlessandisimmediatelyoxidizedinairtoNO2gas.With still more dilute nitric acid, considerable quantities of nitrous oxide

(N2O) are formed; with an active metal like zinc, the product may be theammoniumion(NH4

+).Whennitricacidismixedwithhydrochloricacid,themixtureiscalledaqua

regiabecauseofitsabilitytodissolvegold.

METALS

PropertiesofMetalsSome physical properties of metals are: they have metallic luster, they canconduct heat and electricity, they can be pounded into sheets (aremalleable),theycanbedrawnintowires(areductile),mosthaveasilverycolor,andnoneissolubleinanyordinarysolventwithoutachemicalchange.The general chemical properties ofmetals are: they are electropositive, and

the more active metallic oxides form bases, although some metals form

amphoterichydroxidesthatcanreactasbothacidsandbases.

SomeImportantReductionMethodsofIronOreIronore is refined by reduction ina blast furnace, that is, a large, cylinder-shapedfurnacechargedwithironore(usuallyhematite,Fe2O3), limestone,andcoke.Ahotairblast,oftenenrichedwithoxygen,isblownintothelowerpartofthefurnacethroughaseriesofpipescalledtuyeres.Thechemicalreactionsthatoccurcanbesummarizedasfollows:

Burningcoke:2C+O2→2CO(g)C+O2→CO2(g)

ReductionofCO2:CO2+C→2CO(g)

Reductionofore:Fe2O3+3CO→2Fe+3CO2(g)Fe2O3+3C→2Fe+3CO(g)

Formationofslag:CaCO3→CaO+CO2(g)CaO+SiO2→CaSiO3

Themoltenironfromtheblastfurnaceiscalledpigiron.From pig iron, the molten metal may undergo one of three steel-making

processes that burn out impurities and set the contents of carbon,manganese,sulfur,phosphorus,andsilicon.Oftennickelandchromiumarealloyedinsteeltogivetheparticularpropertiesofhardnessneededfortoolparts.Thethreemostimportantmeansofmakingsteelinvolvethebasicoxygen,theopen-hearth,andtheelectricfurnaces.Thefirsttwomethodsarethemostcommon.Thebasicoxygenfurnaceusesalined“pot”intowhichthemoltenpigironis

poured.Thenahigh-speedjetofoxygenisblownfromawater-cooledlanceintothetopof thepot.This“burnsout” impurities tomakeabatchofsteelrapidlyandcheaply.Theopen-hearth furnace is a large oven containing a dish-shaped area to

hold themolten iron, scrapsteel, andotheradditiveswithwhich it is charged.Alternatingblasts of flame are directed across the surfaceof themeltedmetaluntiltheproperproportionsofadditivesareestablishedforthat“heat”sothatthesteelwillhavetheparticularpropertiesneededbythecustomer.Thetappingof

oneofthesefurnacesholding50to400tonsofsteelisatrulybeautifulsight.The final method of making steel involves the electric arc furnace. This

methodusesenormousamountsofelectricitythroughgraphitecathodesthatareloweredintothemoltenirontopurifyitandproduceahighgradeofsteel.

AlloysAnalloyisamixtureoftwoormoremetals.Inamixturecertainpropertiesofthemetalsinvolvedareaffected.Threeoftheseare:

1.Meltingpoint Themeltingpointofanalloyislowerthanthatofitscomponents.

2.Hardness Analloyisusuallyharderthanthemetalsthatcomposeit.

3.Crystalstructure

Thesizeofthecrystallineparticlesinthealloydeterminesmanyofthephysicalproperties.Thesizeoftheseparticlescanbecontrolledbyheattreatment.Ifthealloycoolsslowly,thecrystallineparticlestendtobelarger.Thus,byheatingandcoolinganalloy,itspropertiescanbealteredconsiderably.

Commonalloysare:

1.Brass,whichismadeupofcopperandzinc.2.Bronze,whichismadeupofcopperandtin.3.Steel,whichhascontrolledamountsofcarbon,manganese,sulfur,phosphorus,andsilicon,isalloyedwithnickelandchromium.

4.Sterlingsilver,whichisalloyedwithcopper.

MetalloidsIn the preceding sections, representative metals and nonmetals have beenreviewed, along with the properties of each. Some elements, however, aredifficult to classify as one or the other.One example is carbon. The diamondformofcarbonisapoorconductor,yet thegraphiteformconductsfairlywell.Neitherformlooksmetallic,socarbonisclassifiedasanonmetal.Silicon looks likeametal.However, itsconductivitypropertiesarecloser to

thoseofcarbon.Sincesomeelementsareneitherdistinctlymetallicnorclearlynonmetallic,a

thirdclass,calledthemetalloids,isrecognized.

The properties of metalloids are intermediate between those of metals andthoseofnonmetals.Althoughmostmetalsformioniccompounds,metalloidsasa group may form ionic or covalent bonds. Under certain conditions puremetalloids conduct electricity, but do so poorly, and are thus termedsemiconductors. This property makes the metalloids important inmicrocircuitry.Themetalloidsarelocatedintheperiodictablealongtheheavydarklinethat

startsalongsideboronanddropsdowninsteplikefashionbetweentheelementsfoundlowerinthetable(seeFigure40).

Figure40.LocationofMetalloids

ChapterSummaryThefollowingtermssummarizealltheconceptsandideasthatwereintroducedinthischapter.Youshouldbeabletoexplaintheirmeaningandhowyouwouldusetheminchemistry.Theyappearinboldfacetypeinthischaptertodrawyourattentiontothem.Theboldfacetypealsomakesiteasierforyoutolookthemupif you need to. You could also use the search or “Google” action on yourcomputer to get a quick and expanded explanation of these terms, laws, andformulas.

acidsalt bronze pigironallotropicform electricarcfurnace resonancestructurealloy metalloid rhombic,monoclinic,basicoxygenfurnace normalsalt amorphousblastfurnace open-hearthfurnace semiconductor

brass

InternetResourcesOnline content that reinforcesmajor concepts discussed in this chapter canbefound at the following Internet addresses if they are still available.Somemayhavebeenchangedordeleted.EssaysOnAlloftheChemicalElementshttp://pubs.acs.org/cen/80th/elements.htmlThis site, taken fromChemical&EngineeringNews, displays a periodic tablewithlinkstoessaysonallofthechemicalelementsbyexpertsintheirfield.ElementalFamilieshttp://www.chemtopics.com/elements.htmThissite,alsotakenfromChemical&EngineeringNews,offersinformationonelementalfamiliesandindividualelementsincludingpictures,shortbackgrounddescriptions,andlinkstoadditionaldata.

PracticeExercises1.Themostactivenonmetallicelementis

(A)chlorine(B)fluorine(C)oxygen(D)sulfur

2.Theorderofdecreasingactivityofthehalogensis

(A)Cl,I,Br(B)F,Cl,Br,I(C)Cl,F,Br,I(D)Cl,Br,I,F

3.Alight-sensitivesubstanceusedonphotographicfilmshastheformula

(A)AgBr

(B)CaF2(C)CuCl(D)MgBr2

4.Sulfurdioxideistheanhydrideof

(A)hydrosulfuricacid(B)sulfurousacid(C)sulfuricacid(D)hyposulfurousacid

5.Thecharringactionofsulfuricacidisduetoitsbeing

(A)astrongacid(B)anoxidizingagent(C)areducingagent(D)adehydratingagent

6.Ammoniaispreparedcommerciallybythe

(A)decompositionofsalts(B)arcprocess(C)combiningofhydrogenandnitrogengases(Haberprocess)(D)contactprocess

7.Anitrogencompoundthathasacoloris

(A)nitricoxide(B)nitrousoxide(C)nitrogendioxide(D)ammonia

8.Ifastudentheatsamixtureofammoniumchlorideandcalciumhydroxideinatesttube,hewilldetect

(A)noreaction(B)theodorofammonia(C)theodorofrotteneggs(D)nitricacidfumes

9.Thedifferencebetweenammoniaandtheammoniumionis

(A)anelectron(B)aneutron(C)aproton(D)hydroxide

10.Animportantoreofironis

(A)bauxite(B)galena(C)hematite(D)smithsonite

11.Areducingagentusedintheblastfurnaceis

(A)CaCO3

(B)CO(C)O2

(D)SiO2

12.Themetalwiththeelectronshellconfigurationof[Ar]3d10s1is

(A)Cu(B)Ag(C)Au(D)Zn(E)Al

13.TheplacementofthehalogenfamilyinthePeriodicTableexplainswhichofthefollowingstatements?

I.Themostactivenonmetallicelementintheperiodictableisfluorine.II.Thenormalphysicalstateofthehalogensgoesfromasolidtoagaseous

stateasyougodownthefamily.III.Thehalogenelementsbecomeionsbyfillingtheoutermostdorbital.

(A)Ionly(B)IIonly(C)IandII(D)IIandIII

(E)IandIII

14.Whichofthefollowingpropertiesareattributedtomostmetals?

I.Theyareconductorsofheatandelectricity.II.Theyaremalleableandductile.III.Theyareallsolidsatroomtemperature.

(A)Ionly(B)IIonly(C)IandII(D)IandIII(E)I,II,andIII

AnswersandExplanations1.(B)Fluorineisthemostactivenonmetallicelementbecauseofitsatomicstructure.Itneedsonlyoneelectrontocompleteitsoutershellandhasthehighestelectronegativity.

2.(B)TheorderofactivityofthehalogensisfromthesmallestatomicradiitothelargeststraightdownthefamilyonthePeriodicTable.

3.(A)Silverbromide,likemanyofthehalogensalts,islightsensitiveandisusedinphotographicfilms.

4.(B)ThereactionofSO2withwaterformssulfurousacid.Theequationis:SO2+H2O→H2SO3.

5.(D)SulfuricacidisastrongdehydratingagentanddrawswatertoitselfsostronglythatiscancharsucrosebywithdrawingthehydrogenandoxygenfromC12H22O11.

6.(C)Thecombiningofhydrogenandnitrogengases(Haberproess)isusedtoprepareammoniacommercially

7.(C)Theonlynitrogencompoundinthelistthathasareddishbrowncolorisnitrogendioxide.

8.(B)Thereactionofthesetwochemicalsresultsintheproductionofammoniumhydroxide,whichisunstableandformsammoniagasandH2O.Thereactionis:2NH4Cl+Ca(OH)2→2NH4OH+CaCl2

Then,becausetheammoniumhydroxideisunstableatroomtemperatures,thisreactionoccurs:NH4OH→NH3↑+H2O.

9.(C)Theammoniamoleculeistrigonalpyramidalwithanunsharedpairofelectronsinonecornerofthepyramid.ThisnegativechargeattractsaH+toformtheammoniumion,NH4

+.

10.(C)Animportantoreofironishematite.

11.(B)CO,carbonmonoxide,isusedintheblastfurnaceasareducingagenttoreactwithoxideimpurities.

12.(A)ThemetalwiththegivenelectronshellconfigurationisCu.Cu,Ag,andAuareallinGroup11,butAgandAuhavehigheratomicnumbersanddifferentelectronshellconfigurations.

13.(A)Becausethehalogenfamily’sphysicalstategoesfromagastoasolidandtheyformionsbycompletingtheouterporbital,theonlytruestatementisI,thatfluorineisthemostactive.

14.(C)Notallmetalsaresolidsatroomtemperature.Mostnotableismercury,whichisaliquidatroomtemperature.

CHAPTER14

CarbonandOrganicChemistry

These skillsareusually testedon theSATSubjectTest inChemistry.Youshouldbeableto…•Describethebondingpatternsofcarbonanditsallotropicforms.•Explainthestructuralpatternandnamingofthealkanes,alkenes,andalkynes,andtheirisomers.

•Showgraphicallyhowhydrocarbonscanbechangedandthedevelopmentofthesefunctionalgroups,theirstructures,andtheirnames:alcohols,aldehydes,ketones,esters,andamines.

Thischapterwillreviewandstrengthentheseskills.BesuretodothePracticeExercisesattheendofthechapter.

Carbon is unique. It forms inorganic substances such as carbon dioxide,graphite, and diamonds. It also forms organic substances without which lifecouldnotexist.Itformsplanarsubstances,tetrahedrons,andrings.

CARBONFormsofCarbonTheelementcarbonoccursmainlyinthreeallotropicforms:diamond,graphite,andamorphous(althoughsomeevidenceshowstheamorphousformshavesomecrystalline structure). In the mid-1980s, fullereneswere identified as a newallotropic form of carbon. They are found in soot that forms when carbon-containingmaterialsareburnedwithlimitedoxygen.Theirstructureconsistsofnear-sphericalcagesofcarbonatomsresemblinggeodesicdomes.The diamond form has a close-packed crystal structure that gives it its

propertyofextremehardness.Initeachcarbonisbondedtofourothercarbonsina tetrahedronarrangement like this:Thesecovalent solids formcrystals thatcanbeviewedasasinglegiantmoleculemadeupofanalmostendlessnumberofcovalentbonds.Becauseallofthebondsinthisstructureareequallystrong,

covalent solids are often very hard, and they are notoriously difficult tomelt.Diamond is the hardest natural substance.At atmospheric pressure, itmelts at3,550°C.

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Allotropicformsofcarbon:

diamond

graphite

amorphous

fullerenes

It has been possible to make synthetic diamonds in machines that subjectcarbon to extremely high pressures and temperatures.Most of these diamondsareusedforindustrialpurposes,suchasdies.The graphite form is made up of planes of hexagonal structures that are

weaklybondedtotheplanesaboveandbelow.Thisexplainsgraphite’sslipperyfeelingandmakesitusefulasadrylubricant.Graphiteisalsomixedwithclaytomake“lead”forleadpencils.Itsstructurecanbeseenbelow.Graphitealsohasthepropertyofbeinganelectricalconductor.

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Diamond uses the sp3 hybridorbitals to explain its tetrahedron

structure.

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Graphite uses the trigonal sp2hybrids

Some common amorphous forms of carbon are charcoal, coke, bone black,andlampblack.

CarbonDioxideCarbondioxide(CO2)isawidelydistributedgasthatmakesup0.04percentofthe air. There is a cycle that keeps this figure relatively stable. It is shown inFigure41.

Figure41.CarbonDioxideCycle

LABORATORYPREPARATIONOFCO2.Theusual laboratorypreparationconsists of reacting calcium carbonate (marble chips) with hydrochloric acid,althoughanycarbonateorbicarbonateandanycommonacidcouldbeused.Thegasiscollectedbywaterdisplacementorairdisplacement.

The test for carbon dioxide consists of passing it through limewater,(Ca(OH)2). If CO2 is present the limewater turns cloudy because of theformationofawhiteprecipitateoffinelydividedCaCO3:

Ca(OH)2(aq)+CO2(g)→CaCO3(s)+H2O( )

ContinuedpassingofCO2 into thesolutionwilleliminate thecloudyconditionbecause the insoluble CaCO3 becomes soluble calcium bicarbonate(Ca(HCO3)2):

CaCO3(s)+H2O( )+CO2(g)→Ca2+(HCO3−)2(aq)

This reaction can easily be reversed with increased temperature or decreasedpressure.Thisisthewaystalagmitesandstalactitesformonthefloorsandroofsof caves, respectively. The ground water containing calcium bicarbonate isdepositedon theroofandfloorof thecaveanddecomposes intosolidcalciumcarbonateformations.

IMPORTANTUSESOFCO2

1.BecauseCO2istheacidanhydrideofcarbonicacid,itformstheacidwhenreactedwithsoftdrinks,thusmakingthem“carbonated”beverages.

CO2(g)+H2O( )→H2CO3(aq)

2.Solidcarbondioxide(−78°C),or“dryice,”isusedasarefrigerantbecauseithastheadvantageofnotmeltingintoaliquid;instead,itsublimesandintheprocessabsorbs3timesasmuchheatpergramasice.

3.FireextinguishersmakeuseofCO2becauseofitspropertiesofbeingtimesheavierthanairandnotsupportingordinarycombustion.ItisusedintheformofCO2extinguishers,whichreleaseCO2fromasteelcylinderintheformofagastosmotherthefire.

4.PlantsconsumeCO2inthephotosynthesisprocess,inwhichchlorophyll(thecatalyst)andsunlight(theenergysource)mustbepresent.The

reactantsandproductsofthisreactionare:

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Knowthephotosynthesisprocess.

ORGANICCHEMISTRYOrganicchemistrymaybedefinedsimplyasthechemistryofthecompoundsofcarbon. Since Friedrich Wöhler synthesized urea in 1828, chemists havesynthesized thousands of carbon compounds in areas of dyes, plastic, textilefibers, medicines, and drugs. The number of organic compounds has beenestimatedtobeintheneighborhoodofamillionandconstantlyincreasing.Thecarbonatom(atomicnumber6)hasfourelectronsinitsoutermostenergy

level,whichshowatendencytobeshared(electronegativityof2.5)incovalentbonds. By this means, carbon bonds to other carbons, hydrogens, halogens,oxygen,andotherelementstoformthemanycompoundsoforganicchemistry.

HYDROCARBONSHydrocarbons,asthenameimplies,arecompoundscontainingonlycarbonandhydrogen in their structures. The simplest hydrocarbon is methane, CH4. Aspreviouslymentioned,thistypeofformula,whichshowsthekindsofatomsandtheir respectivenumbers, is calledanempirical formula. In organic chemistrythis is not sufficient to identify the compound it is used to represent. Forexample,theempiricalformulaC2H6Ocoulddenoteeitheranetheroranethylalcohol.Forthisreason,astructuralformulaisusedtoindicatehowtheatomsarearrangedinthemolecule.TheetherofC2H6Olookslikethis:

whereastheethylalcoholisrepresentedbythisstructuralformula:

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Organic chemistry makes use ofstructural formulas to show atomicarrangements.

To avoid ambiguity, structural formulas are more often used than empiricalformulasinorganicchemistry.Thestructuralformulaofmethaneis

AlkaneSeries(Saturated)Methane is the first member of a hydrocarbon series called the alkanes (orparaffin series).Thegeneral formula for this series isCnH2n+2,wheren is thenumber of carbons in the molecule. Table 14 provides some essentialinformationabout thisseries.Sincemanyotherorganicstructuresusethestemof thealkanenames,youshould learn thesenamesandstructureswell.Noticethat, as the number of carbons in the chain increases, the boiling point alsoincreases.Thefirst fouralkanesaregasesat roomtemperature; thesubsequentcompoundsareliquid, thenbecomemoreviscouswithincreasinglengthof thechain.

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Alkanes are CnH2n+2. They arehomologous.

Since the chain is increased by a carbon and two hydrogens in eachsubsequentmolecule,thealkanesarereferredtoasahomologousseries.

The alkanes are found in petroleum and natural gas. They are usuallyextracted by fractional distillation,which separates the compounds by varyingthetemperaturesothateachvaporizesatitsrespectiveboilingpoint.

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Learn the names of the first 10alkanes.

When the alkanes are burnedwith sufficient air, the compounds formed areCO2andH2O.Anexampleis:

2C2H6(g)+7O2(g)→4CO2(g)+6H2O(g)

Thealkanescanbereactedwithhalogenssothathydrogensarereplacedbyahalogenatom:Thesearecalledalkylhalides.

Somecommonsubstitutioncompoundsofmethaneare:

NAMINGALKANESUBSTITUTIONS.Whenanalkanehydrocarbonhasanend hydrogen removed, it is referred to as an alkyl substituent or group. Therespectivenameofeachisthealkanenamewith-anereplacedby-yl.Thesearecalledalkylgroups.

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Replace-anewith -yl to form alkylgroups.

Onemethodof naming a substitutionproduct is to use the alkyl name for therespectivechainandthehalideasshownabove.Thehalogentakestheformoffluoro-,bromo-,iodo-,andsoon,dependingonthehalogen,andisattachedtoanalkanename.Itprecedesthealkanename,asshownaboveinbromomethaneand1-chlorobutane.The IUPACsystemuses thenameof the longest carbonchainas theparent

chain. The carbon atoms are numbered in the parent chain to indicate wherebranchingor substitution takesplace.Thedirectionofnumbering ischosensothat the lowest numbers possible are given to the side chains. The completenameofthecompoundisarrivedatbyfirstnamingtheattachedgroup,eachofthese being prefixed by the number of the carbon towhich it is attached, andthen the parent alkane. If a particular group appears more than once, theappropriate prefix (di, tri, and so on) is used to indicate howmany times thegroupappears.Acarbonatomnumbermustbeusedto indicate thepositionofeach such group. If two ormore of the same group are attached to the samecarbonatom,thenumberofthecarbonatomisrepeated.Iftwoormoredifferentsubstitutedgroupsareinaname,theyarearrangedalphabetically.

EXAMPLE12,2-dimethylbutane

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Numbers have been added to thelongestchainforidentificationonly.

EXAMPLE21,1-dichloro-3-ethyl-2,4-dimethylpentane

EXAMPLE32-iodo-2-methylpropane

CYCLOALKANES.Startingwithpropaneinthealkaneseries,itispossibletoget a ring form by attaching the two chain ends. This reduces the number ofhydrogensbytwo.

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Cycloalkanes form single-bondedringcompounds.

Cycloalkanes are named by adding the prefix cyclo- to the name of thestraight-chainalkanewiththesamenumberofhydrocarbons,asshownabove.Whenthereisonlyonealkylgroupattachedtothering,nopositionnumberis

necessary.When there is more than one alkyl group attached to the ring, thecarbonatomsintheringarenumberedtogivethelowestnumberspossibletothealkylgroups.Thismeansthatoneofthealkylgroupswillalwaysbeinposition1.ThegeneralformulaisCnH2n.Hereisanexample:

Iftherearetwoormorealkylgroupsattachedtothering,numberthecarbonatomsinthering.Assignpositionnumberonetothealkylgroupthatcomesfirstinalphabeticalorder,thennumberinthedirectionthatgivestherestofthealkylgroupsthelowestnumberspossible.Because all themembers of the alkane series have single covalent bonds, thisseriesandallsuchstructuresaresaidtobesaturated.If the hydrocarbon molecule contains double or triple covalent bonds, it is

referredtoasunsaturated.

PROPERTIESANDUSESOFALKANES.Propertiesforsomestraight-chainalkanesareindicatedinTable14.Thetrendsinthesepropertiescanbeexplainedby examining the structures of alkanes. The carbon-hydrogen bonds arenonpolar. The only forces of attraction between nonpolarmolecules are weakintermolecular,orLondondispersion,forces.Theseforcesincreaseasthemassofamoleculeincreases.

The tablealsoshows thephysicalstatesofalkanes.Smalleralkanesexistasgases at room temperature, while larger ones exist as liquids. Gasoline andkeroseneconsistmostlyof liquidalkanes.Seventeencarbonsareneededinthechainforthesolidformtooccur.Paraffinwaxcontainssolidalkanes.Thedifferencesintheboilingpointsofmixturesoftheliquidalkanesfoundin

petroleummake it possible to separate the various components by fractionaldistillation.Thisisthemajorindustrialprocessusedinrefiningpetroleumintogasoline,kerosene,lubricatingoils,andseveralotherminorcomponents.

AlkeneSeries(Unsaturated)The alkene series has a double covalent bond between two adjacent carbonatoms.ThegeneralformulaofthisseriesisCnH2n.Innamingthesecompounds,thesuffixofthealkaneisreplacedby-ene.Twoexamples:

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AlkeneshavetheformCnH2n.

Namingamorecomplexexampleis:

Thepositionnumberandnameofthealkylgroupareinfrontofthedouble-bond position number. The alkyl group above is an ethyl group. It is on thesecondcarbonatomoftheparenthydrocarbon.Thenameis:2-ethyl-1-penteneIfthedoublebondoccursonaninteriorcarbon,thechainisnumberedsothat

the position of the double bond is designated by the lowest possible numberassignedtothefirstdoublybondedcarbon.Forexample:

Thebondingismorecomplexinthedoublecovalentbondthaninthesinglebondsinthemolecule.Usingtheorbitalpicturesoftheatom,wecanshowthisasfollows:

Thetwoplobesattachedaboveandbelowconstituteonebondcalledapi(π)bond.The sp2 orbital bonds between the carbons and with each hydrogen are

referredtoassigma(σ)bonds.

AlkyneSeries(Unsaturated)Thealkyneserieshas a triple covalentbondbetween twoadjacent carbons.

Thegeneral formulaof thisseries isCnH2n-2. Innaming thesecompounds, thealkanesuffixisreplacedby-yne.Twoexamples:

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AlkyneshavetheformCnH2n–2.

Theorbitalstructureofethynecanbeshownasfollows:Thebondsformedbytheporbitalsandtheonebondbetweenthesporbitals

makeupthetriplebond.

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Notice thatpibondsarebetweenporbitals and that sigma bonds arebetweensandporbitals.

Theprecedingexamplesshowonlyonetriplebond.Ifthereismorethanonetriple bond, modify the suffix to indicate the number of triple bonds. Forexample,2wouldbeadiyne,3wouldbeatriyne,andsoon.Nextaddthenamesofthealkylgroupsiftheyareattached.Numberthecarbonatomsinthechainsothatthefirstcarbonatominthetriplebondnearesttheendofthechainhasthelowestnumber. Ifnumbering frombothendsgives the samepositions for twotriplebonds,thennumberfromtheendnearestthefirstalkylgroup.Then,placethe position numbers of the triple bonds immediately before the name of theparent hydrocarbon alkyne and place the alkyl group position numbersimmediatelybeforethenameofthecorrespondingalkylgroup.Twomoreexamplesofalkynesare:

Namingamorecomplexexampleis:

Thepositionnumberandthenameofthealkylgroupareplacedinfrontofthedouble-bondpositionnumber.Thealkylgroupaboveisanethylgroup.Itisonthesecondcarbonatomoftheparenthydrocarbon.

Thenameis:2-ethyl-1-pentyne

AromaticsThearomaticcompoundsareunsaturatedringstructures.Thebasicformulaof

this series is CnH2n-6, and the simplest compound is benzene (C6H6). Thebenzenestructureisaresonancestructurethatisrepresentedlikethis:

Note: The carbon-to-carbon bonds are neither single nor double bonds buthybridbonds.Thisstructuralrepresentationiscalledresonancestructures.

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C6H6, benzene is the simplestaromaticcompound.

Thebenzeneresonancestructurecanalsobeshownlikethis:

Theorbitalstructurecanberepresentedlikethis:

Mostofthearomaticshaveanaroma,thusthename“aromatic.”TheC6H5group isasubstituentcalledphenyl.This is thebenzenestructure

withonehydrogenmissing. If thephenyl substituentaddsamethylgroup, thecompoundiscalledtolueneormethylbenzene.

Twoothermembersofthebenzeneseriesandtheirstructures:

TheIUPACsystemofnamingbenzenederivatives,aswithchaincompounds,involves numbering the carbon atoms in the ring in order to pinpoint thelocationsofthesidechains.However,ifonlytwogroupsaresubstitutedinthebenzene ring, the compound formedwill be abenzenederivativehaving threepossible isomeric forms. In suchcases, theprefixesortho-,meta-, andpara-,abbreviated aso-,m, andp-,may be used to name the isomers. In the ortho-structure,thetwosubstitutedgroupsarelocatedonadjacentcarbonatoms.Inthemeta- structure, they are separatedbyone carbonatom. In thepara- structure,

theyareseparatedbytwocarbonatoms.

IsomersManyofthechainhydrocarbonscanhavethesameformula,buttheirstructuresmaydiffer.Forexample,butaneisthefirstcompoundthatcanhavetwodifferentstructuresorisomersforthesameformula.

Thisisomerizationcanbeshownbythefollowingequation:

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REMEMBER Isomers have thesame formula but differentstructures.

Theisomershavedifferentproperties,bothphysicalandchemical,fromthoseofhydrocarbonswiththenormalstructure.

HYDROCARBONDERIVATIVESAlcohols—MethanolandEthanolThe simplest alcohols are alkanes that have one or more hydrogen atomsreplacedbythehydroxylgroup,—OH.Thisiscalleditsfunctionalgroup.

•MethanolMethanolisthesimplestalcohol.Itsstructureis

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Alcohol’s functional group is R—OH.Ahydroxylgroupisattachedtoanalkylstem.

PROPERTIESANDUSES.Methanol is a colorless, flammable liquidwith aboilingpointof65°C. It ismisciblewithwater, is exceedinglypoisonous, andcancauseblindnessiftakeninternally.Itcanbeusedasafuel,asasolvent,andasadenaturanttomakeethylalcohol,unsuitablefordrinking.

•EthanolEthanolisthebestknownandmostusedalcohol.Itsstructureis

Itscommonnamesareethylalcoholandgrainalcohol.

PROPERTIES AND USES. Ethanol is a colorless, flammable liquid with aboilingpointof78°C.Itismisciblewithwaterandisagoodsolventforawide

varietyofsubstances(thesesolutionsareoftenreferredtoas“tinctures”).Itcanbe used as an antifreeze because of its low freezing point, -115°C, and formakingacetaldehydeandether.Itispresentlyusedingasolineasanalternativetoreducetheuseofpetroleum.

OtherAlcoholsIsomericalcoholshavesimilarformulasbutdifferentpropertiesbecauseoftheirdifferencesinstructure.Ifthe—OHisattachedtoanendcarbon,thealcoholiscalled a primary alcohol. If attached to a “middle” carbon, it is called asecondaryalcohol.Someexamples:

The number in front of the name indicates to which carbon the—OH ion isattached.

Otheralcoholswithmorethanone—OHgroup:

A colorless liquid, high boiling point, low freezing point. Used as permanentantifreezeinautomobiles.

Colorless liquid, odorless, viscous, sweet taste. Used to make nitroglycerine,

resinsforpaint,andcellophane.

Aldehydes

The functional group of an aldehyde is the formyl group. The general

formulaisRCHO,whereRrepresentsahydrocarbonradical.

PREPARATIONFROMANALCOHOL.Aldehydescanbepreparedby theoxidationofanalcohol.Thiscanbedonebyinsertingahotcopperwireintothealcohol.Atypicalreactionis:

Themiddlestructureisanintermediatestructure;sincetwohydroxylgroupsdonotstayattached to thesamecarbon, itchanges to thealdehydebyawatermolecule“breakingaway.”Thealdehydenameisderivedfromthealcoholnamebydroppingthe-oland

adding-al.Ethanolformsethanal(acetaldehyde)inthesamemanner.

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The aldehyde functional group is

Aformylgroupisattachedtoanalkylstem.

OrganicAcidsorCarboxylicAcids

The functional group of an organic acid is the , carboxyl group. The

generalformulaisR—COOH.

PREPARATIONFROMANALDEHYDE.Organicacidscanbepreparedbythemildoxidationofanaldehyde.Thesimplestacidismethanoicacid,whichispresentinants,bees,andotherinsects.Atypicalreactionis:

Notice that in theIUPACsystemthename isderivedfromthealkanestembyadding-oic.

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The carboxyl group is the functionalgroup of an organic acid. It is

Ethanalcanbeoxidizedtoethanoicacid:

Acetic acid, as ethanoic acid is commonlycalled, is amild acid that, in theconcentrated form, is called glacial acetic acid. Glacial acetic acid is used inmanyindustrialprocesses,suchasmakingcelluloseacetate.Vinegarisa4%to8%solutionofaceticacidthatcanbemadebyfermentingalcohol.

Itispossibletohavemorethanonecarboxylgroupinacarboxylicacid.Intheethanederivative,itwouldbeethanedioicacidwithastructurelikethis:

SummaryofOxygenDerivatives

Note: R1 indicates a hydrocarbon chain different from R by having one lesscarboninthechain.Anactualexampleusingethane:

KetonesWhenasecondaryalcoholisslightlyoxidized,itformsacompoundhavingthefunctionalgroup ,andcalledaketone.TheR1indicatesthatthisgroup

neednotbethesameasR.Anexampleis:

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Note that the functional group ofketonesis

Exampleinalongerchain:

In the IUPACmethod thenameof theketonehas theending -onewithadigitindicatingthecarbonthathasthedouble-bondedoxygenprecedingtheendinginlargerchains,asshowninbutan-2-one.Anothermethodofdesignatingaketoneis toname the radicalsoneither sideof theketonestructureanduse thewordketone.Intheprecedingreaction,theproductwouldbedimethylketone.Note that both aldehydes and ketones contain the carbonyl group in their

structures.Inthealdehydes, it isat theendofthechain,and, inacids, it is theinteriorofthechain.

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The functional groupof ethers isR—O—R1

EthersWhen a primary alcohol, such as ethanol, is dehydratedwith sulfuric acid, anetherforms.ThefunctionalgroupisR—O—R1, in which R1 may be the same hydrocarbon group, as shown inexample1below,oradifferenthydrocarbongroup,asshowninexample2.

1.

2.Anotheretherwithunlikegroups,R—O—R1:

IntheIUPACmethod,theethername,asshownintheexamples,ismadeupof two attached alkyl chains to the oxygen. The shorter of the two chainsbecomesthefirstpartofthename,withthe–anesuffixchangedto–oxyandthenameof the longer alkanechainas the suffix.Examples are ethoxyethaneandethoxypropane.Diethyletheriscommonlyreferredtoasetherandisusedasananesthetic.

AminesandAminoAcidsThe group NH2

− is found in the amide ion and the amino group. Under theproper conditions, the amide ion can replace a hydrogen in a hydrocarboncompound.Theresultingcompoundiscalledanamine.Twoexamples:

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The amide functional group is

Inamides,theNH2−groupreplacesahydrogeninthecarboxylgroup.When

namingamides,the-icofthecommonnameorthe-oicoftheIUPACnameoftheparentacidisreplacedby-amide.Forexample:

Amino acids are organic acids that contain one ormore amino groups.Thesimplest uncombined amino acid is glycine, or amino acetic acid,NH2CH2—COOH.Morethan20aminoacidsareknown,abouthalfofwhichareessentialinthehumandietbecausetheyareneededtomakeupthebodyproteins.

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Esterscanbecomparedtoinorganicsalts.

EstersEsters are often compared to inorganic salts because their preparations aresimilar. Tomake a salt, you react the appropriate acid and base. Tomake anester,youreacttheappropriateorganicacidandalcohol.Forexample:

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Note the functional group

Thenameismadeupofthealkylsubstituentofthealcoholandtheacidname,inwhich-icisreplacedwith-ate.Thegeneralequationis:

Estersusuallyhavesweetsmellsandareusedinperfumesandflavorextracts.

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Notethefunctionalgroup

Thefollowingchartsummarizestheorganicstructuresandformulasdiscussedinthissection.

ChapterSummaryThefollowingtermssummarizealltheconceptsandideasthatwereintroducedinthischapter.Youshouldbeabletoexplaintheirmeaningandhowyouwouldusetheminchemistry.Theyappearinboldfacetypeinthischaptertodrawyourattentiontothem.Theboldfacetypealsomakesiteasierforyoutolookthemupif you need to. You could also use the search or “Google” action on yourcomputer to get a quick and expanded explanation of these terms, laws, and

formulas.

alcohol aromatics isomeraldehyde diamond ketonealkane ester ortho-,meta-,parapositionsalkene ether photosynthesisalkylgroups fullerene saturatedhydrocarbonalkyne functionalgroups unsaturatedhydrocarbonamine hydrocarbonaminoacid

InternetResourcesOnline content that reinforcesmajor concepts discussed in this chapter canbefound at the following Internet addresses if they are still available.Somemayhavebeenchangedordeleted.TheChemistryofCarbonhttp://www.nyu.edu/pages/mathmol/modules/carbon/carbon1.htmlThissiteoffersaninterestingtutorialonthechemistryofcarbon.OrganicNomenclaturehttp://en.wikipedia.org/wiki/IUPAC_nomenclature_of_organic_chemistry#Halogens_.28Alkyl_halides.29Thiswebsiteoffersatutorialonnamingorganiccompounds.

PracticeExercises

1.Carbonatomsusually

(A)lose4electrons(B)gain4electrons(C)form4covalentbonds(D)sharethe2electronsinthefirstprincipalenergylevel

2.Cokeisproducedfrombituminouscoalby

(A)cracking(B)synthesis

(C)substitution(D)destructivedistillation

3.Theusualmethodforpreparingcarbondioxideinthelaboratoryis

(A)heatingacarbonate(B)fermentation(C)reactinganacidandacarbonate(D)burningcarbonaceousmaterials

4.Theprecipitateformedwhencarbondioxideisbubbledintolimewateris

(A)CaCl2(B)H2CO3

(C)CaO(D)CaCO3

5.The“lead”inaleadpencilis

(A)boneblack(B)graphiteandclay(C)leadoxide(D)leadperoxide

6.Thefirstandsimplestalkaneis

(A)ethane(B)methane(C)C2H2

(D)methene(E)CCl4

7.Slightoxidationofaprimaryalcoholgives

(A)aketone(B)anorganicacid(C)anether(D)analdehyde(E)anester

8.Thecharacteristicgroupofanorganicesteris

(A)—CO—(B)—COOH(C)—CHO(D)—O—(E)—COO—

9.Theorganicacidthatcanbemadefromethanolis

(A)aceticacid(B)formicacid(C)C3H7OH(D)foundinbeesandants(E)butanoicacid

10.Anestercanbepreparedbythereactionof

(A)twoalcohols(B)analcoholandanaldehyde(C)analcoholandanorganicacid(D)anorganicacidandanaldehyde(E)anacidandaketone

11.Compoundsthathavethesamecompositionbutdifferintheirstructuralformulas

(A)areusedforsubstitutionproducts(B)arecalledisomers(C)arecalledpolymers(D)havethesameproperties(E)areusuallyalkanes

12.Etheneisthefirstmemberofthe

(A)alkaneseries(B)saturatedhydrocarbons(C)alkyneseries(D)unsaturatedhydrocarbons(E)aromatichydrocarbons

ThefollowingquestionsareintheformatthatisusedontheSATSubjectTestinChemistry.Ifyouarenotfamiliarwiththesetypesofquestions,studybeforedoingtheremainderofthereviewquestions.

Directions: Each of the following sets of lettered choices refers to thenumberedquestionsimmediatelybelowit.Foreachnumbereditem,choosetheoneletteredchoicethatfits itbest.Everychoiceinasetmaybeusedonce,morethanonce,ornotatall.

Questions13–20

(A)CH3–CH2–CH3

(C)CH3–O–C3H7

13.Whichorganicstructureisethylamine?

14.Whichorganicstructureismethylpropylether(methoxypropane)?

15.Whichorganicstructureispropane?

16.Whichorganicstructureisethanoicacid?

17.Whichorganicstructureispropanone?

Questions18–20

Usingthesamechoices,matchthefunctionalgroupsnamedtothestructurethatcontainsit.

18.Whichstructurecontainsanorganicacidfunctionalgroup?

19.Whichstructurecontainsaketonegrouping?

20.Whichstructurecontainsanaminegroup?

AnswersandExplanations1.(C)Becausecarbonhas4electronsinitsouterenergylevel,itusuallyformsfourcovalentbondstofilleachoffoursp3orbitals.

2.(D)Bituminouscoalhastoomuchgaseousimpuritiestoburnatahightemperatureneededtorefineironore.Itisheatedincokeovenstoformthehotterandcleanerburningcoke.

3.(C)ThereactionofanacidandacarbonateistheusualwaytoprepareCO2.

4.(D)Thereactionis:CO2+Ca(OH)2→CaCO3↓+H2O.

5.(B)Theleadinaleadpencilisamixtureofgraphiteandclay.

6.(B)Thefirstalkaneismethane,CH4.

7.(D)Theslightoxidationofaprimaryalcoholproducedanaldehyde.

Anexampleis:

8.(E)Thefunctionalgroupforanesterisshownas–COO–.

9.(A)Ethanolcanbeoxidizedintotheorganicacidenthanoicacid,whichhasthecommonnameofaceticacid.

10.(C)Theformationofanesterisfromthereactionofanorganicacidandanalcohol.Thegeneralequationis:

11.(B)Isomersarecompoundsthathavethesamecompositionbutdifferintheirstructuralformulas.

12.(D)Etheneisthefirstmemberofthealkeneseriesthathasonedoublebond.Becauseithasadoublebond,itissaidtobeunsaturated.Thealkaneseries,whichhasallsinglebondsbetweenthecarbonatomsinthechain,iscalledasaturatedseries.

13.(E)TheNH2−group,calledanaminegroup,makesthisstructure

ethylamine.Thistypeoforganicstructureiscalledanamide.

14.(C)Themethyl(CH3–)groupandthepropyl(–C3H7)groupattachedtoacenteroxygen(–O–)makesthismethylpropylether(methoxypropane).

15.(A)Propaneisthethirdmemberofthealkaneseries,whichismadeupofachainofsingle-bondedcarbonsandhydrogenswiththegeneralformulaofCnH2n+2.

16.(B)Ethanoicacidiscomposedofamethylgroupattachedtothecarboxylgroup(-COOH).Thelatteristhefunctionalgroupforanorganicacid.

17.(D)Thepropan-partofthenametellsyouitsbasicstructureisfrompropane,whichisathree-carbonalkane.The–oneparttellsyouitisaketonethathasadouble-bondedoxygenattachedtothesecondcarboninthechain.

18.(B)Theethanoicacidcontainsthecarboxylgroup(-COOH)thatisshownin(B).Thisistheidentifyingfunctionalgroupfororganicacids.

19.(D)Thefunctionalgroupforketonesisacarboninthechaindouble

bondedtoanoxygenatom(– –).Thenumberinthefronttellsyouwhichcarbonhasthedouble-bondedoxygenattachedtoit.

20.(E)Theaminegroupisthenitrogenwithtwohydrogens,(-NH2),attachedtoachaincarbon.Thesearebasictotheaminoacidstructuresinthebody.

CHAPTER15

TheLaboratory

TheseskillsareusuallytestedontheSATSubjectTestinChemistry.Youshouldbeableto...•Name,identify,andexplainproperlaboratoryrulesandprocedures.•Identifyandexplaintheproperuseoflaboratoryequipment.•Uselaboratorydataandobservationstomakeproperinterpretationsandconclusions.

This chapter will review and strengthen these skills. Be sure to do thePracticeExercisesattheendofthechapter.

Laboratorysetupsvary fromschool toschooldependingonwhether the lab isequipped with macro- or microscale equipment. Microlabs use specializedequipmentthatallowslabworktobedoneonamuchsmallerscale.Thebasicprinciples are the same as when using full-sized equipment, but microscaleequipment lowers the cost of materials, results in less waste, and poses lessdanger.Theexamplesinthisbookareofmacroscaleexperiments.Alongwithlearningtousemicroscaleequipment,mostlabsrequireastudent

to learn how to use technological tools to assist in experiments. The mostcommonare:Gravimetricbalancewithdirectreadingstothousandthsofagraminstead

ofatriple-beambalancepHmetersthatgivepHreadingsdirectlyinsteadofusingindicatorsSpectrophotometer, which measures the percentage of light transmitted at

specificfrequenciessothatthemolarityofasamplecanbedeterminedwithoutdoingatitrationComputer-assisted labs that use probes to take readings, e.g., temperature

andpressure,sothatprogramsavailableforcomputerscanprintoutagraphoftherelationshipofreadingstakenovertime

LABORATORYSAFETYRULES

TheTenCommandmentsofLabSafetyThefollowingisasummaryofrulesyoushouldbewellawareofinyourownchemistrylab.

1.Dressappropriatelyforthelab.Wearsafetygogglesandalabapronorcoat.Tiebacklonghair.Donotwearopen-toedshoes.

2.Knowwhatsafetyequipmentisavailableandhowtouseit.Thisincludestheeyewashfountain,fireblanket,fireextinguisher,andemergencyshower.

3.Knowthedangersofthechemicalsinuse,andreadlabelscarefully.Donottasteorsniffchemicals.

4.Disposeofchemicalsaccordingtoinstructions.Usedesignateddisposalsites,andfollowtherules.Neverreturnunneededchemicalstotheoriginalcontainers.

5.Alwaysaddacidsandbasestowaterslowlytoavoidsplattering.Thisisespeciallyimportantwhenusingstrongacidsandbasesthatcangeneratesignificantheat,formsteam,andsplashoutofthecontainer.

6.Neverpointheatingtesttubesatyourselforothers.Beawareofreactionsthatareoccurringsothatyoucanremovethemfromtheheatifnecessarybeforethey“shoot”outofthetesttube.

7.Donotpipetteanythingbymouth!Neveruseyourmouthasasuctionpump,notevenathomewithtoxicorflammableliquids.

8.Usethefumehoodwhendealingwithtoxicfumes!Ifyoucansmellthem,youareexposingyourselftoadosethatcanharmyou.

9.Donoteatordrinkinthelab!Itistooeasytotakeinsomedangeroussubstanceaccidentally.

10.Followalldirections.Neverhaphazardlymixchemicals.Payattentiontotheorderinwhichchemicalsaretobeaddedtoeachother,anddonotdeviate!

SOMEBASICSETUPSThroughout this book, drawings of laboratory setups that serve specific needshavebeenpresented.Youshouldbefamiliarwiththeassemblyanduseofeachofthesesetups.

•Preparationofagaseousproduct,nonsolubleinwater,bywaterdisplacementfromsolidreactants

•Preparationofagaseousproduct,nonsolubleinwater,bywaterdisplacementfromatleastonereactantinsolution

•Distillationofaliquid

•Titration

The following are additional laboratory setups with which you should befamiliar:

1.PREPARATIONOFAGASEOUSPRODUCT,SOLUBLEINWATERANDLIGHTERTHANAIR,BYTHEDOWNWARDDISPLACEMENTOFAIR.SEEFIGURE42.

EXAMPLE:Preparationofammonia(NH3).

2NH4Cl(s)+Ca(OH)2(s)→CaCl2(s)+2H2O(g)2NH3(g)

Figure42.PreparationofAmmonia

2.SEPARATIONOFAMIXTUREBYCHROMATOGRAPHY.SEE

FIGURE43.

Figure43.ChromatographySetup

EXAMPLE:Chromatographyisaprocessusedtoseparatepartsofamixture.Thecomponentpartsseparateasthesolventcarriermovespastthespotofmaterialtobeseparatedbycapillaryaction.Becauseofvariationsinsolubility,attractiontothefilterpaper,anddensity,eachfractionmovesatadifferentrate.Onceseparationoccurs,thefractionsareeitheridentifiedbycolororremovedforothertests.AusualexampleistheuseofShaefferSkripInkNo.32,whichseparatesintoyellow,red,andbluestreaksofdyes.

3.MEASURINGPOTENTIALSINELECTROCHEMICALCELLS.SEEFIGURE44.

Figure44.PotentiometerSetupforMeasuringPotential

EXAMPLE:Thevoltmeterinthiszinc-silverelectrochemicalcellwouldreadapproximately1.56V.ThismeansthattheAgtoAg+half-cellhas1.56Vmoreelectron-attractingabilitythantheZntoZn2+half-cell.Ifthepotentialofthezinchalf-cellwereknown,thepotentialofthesilverhalf-cellcouldbedeterminedbyadding1.56Vtothepotentialofthezinchalf-cell.Inasetuplikethis,onlythedifferenceinpotentialbetweentwohalf-cellscanbemeasured.Noticetheuseofthesaltbridgeinsteadofaporousbarrier.

4.REPLACEMENTOFHYDROGENBYAMETAL.SEEFIGURE45.

Figure45.EudiometerApparatus

EXAMPLE:Measurethemassofastripofmagnesiumwithananalyticalbalancetothenearest0.001g.Usingacoiledstripwithamassofabout0.040gproducesabout40mLofH2.Pour5mLofconcentratedHClintoaeudiometer,andslowlyfilltheremainderwithwater.Trytominimizemixing.LowerthecoilofMgstripintothetube,invertit,andlowerittothebottomofthebeaker.Afterthereactioniscomplete,youcanmeasurethevolumeofthegasreleasedandcalculatethemassofhydrogenreplacedbythemagnesium.(RefertoChapter5foradiscussionofgaslaws.)

SUMMARYOFQUALITATIVETESTS

I.IdentificationofSomeCommonGasesGas Test ResultAmmonia 1.Smellcautiously. 1.Sharpodor.NH3 2.Testwithlitmus. 2.Redlitmusturnsblue. 3.ExposetoHClfumes. 3.Whitefumesform,NH4Cl.Carbondioxide 1.Passthroughlimewater, 1.Whiteprecipitateforms,CO2 Ca(OH)2 CaCO3

Carbonmonoxide 1.Burnitandpassproductthrough

CO limewater,Ca(OH)2 1.Whiteprecipitateforms,CaCO3

HydrogenH2

1.Allowittomixwithsomeair,thenignite. 1.Gasexplodes.

2.Burnit—trapproduct.2.Burnswithblueflame—productH2Oturnscobaltchloridepaperfrombluetopink.

Hydrogenchloride 1.Smellcautiously. 1.Chokingodor.HCl 2.Exhaleoverthegas. 2.Vaporfumesform.

3.Dissolveinwaterandtestwithlitmus. 3.Bluelitmusturnsred.4.AddAgNO3tothesolution. 4.Whiteprecipitateforms.

Hydrogensulfide 1.Smellcautiously. 1.Rotteneggodor.H2S 2.Testwithmoistleadacetatepaper. 2.Turnsbrown-black(PbS).Oxygen 1.Insertglowingsplint. 1.Burstsintoflame.O2 2.Addnitricoxidegas. 2.Turnsreddishbrown.

II.IdentificationofSomeNegativeIonsIon Test ResultAcetate AddconcentratedH2SO4andwarm Odorofvinegarreleased.

C2H3O2− gently.

CarbonateCO3

−AddHClacid;passreleasedgasthroughlimewater. White,cloudyprecipitateforms.

Chloride 1.Addsilvernitratesolution. 1.Whiteprecipitateforms.

Cl−2.Thenaddnitricacid,laterfollowedbyammoniumhydroxide.

2.PrecipitateinsolubleinHNO3butdissolvesinNH4OH.

Hydroxide Testwithredlitmuspaper. Turnsblue.

OH−

Sulfate AddsolutionofBaCl2,thenHCl. Whiteprecipitateforms;insolubleinHCl.

SO4−

SulfideS2−

AddHClandtestgasreleasedwithleadacetatepaper.

Gas,withrotteneggodor,turnspaperbrown-black.

III.IdentificationofSomePositiveIonsIon Test ResultAmmonium Addstrongbase(NaOH); Odorofammonia.

NH4+ heatgently.

FerrousFe2+

Addsolutionofpotassiumferricyanide,K3Fe(CN)6

Darkblueprecipitateforms(Turnball’sblue).

FerricFe3+

Addsolutionofpotassiumferrocyanide,K4Fe(CN)6.

Darkblueprecipitateforms(Prussianblue).

Hydrogen Testwithbluelitmuspaper. Turnsred.

H+

IV.QualitativeTestsofSomeMetals

FLAME TESTS. Carefully clean a platinum wire by dipping it into diluteHNO3andheatingintheBunsenflame.Repeatuntiltheflameiscolorless.Dipheatedwire into the substancebeing tested (either solid or solution), and thenholditinthehotouterpartoftheBunsenflame.Compoundof ColorofFlameSodium(Na) YellowPotassium(K) Violet(usecobalt-blueglasstoscreenoutNaimpurities)Lithium(Li) CrimsonCalcium(Ca) Orange-redBarium(Ba) GreenStrontium(Sr) Brightred

HYDROGEN SULFIDE TESTS. Bubble hydrogen sulfide gas through thesolutionofasaltofthemetalbeingtested.Checkcoloroftheprecipitateformed.Compoundof ColorofSulfidePrecipitateLead(Pb) Brown-black(PbS)Copper(Cu) Black(CuS)Silver(Ag) Black(Ag2S)Mercury(Hg) Black(HgS)Nickel(Ni) Black(NiS)Iron(Fe) Black(FeS)Cadmium(Cd) Yellow(CdS)Arsenic(As) Lightyellow(As2S3)

Antimony(Sb) Orange(Sb2S3)Zinc(Zn) White(ZnS)Bismuth(Bi) Brown(Bi2S3)

ChapterSummaryThefollowingtermssummarizealltheconceptsandideasthatwereintroducedinthischapter.Youshouldbeabletoexplaintheirmeaningandhowyouwouldusetheminchemistry.Theyappearinboldfacetypeinthischaptertodrawyourattentiontothem.Theboldfacetypealsomakesiteasierforyoutolookthemup

if you need to. You could also use the search or “Google” action on yourcomputer to get a quick and expanded explanation of these terms, laws, andformulas.

gravimetricbalancewithdirectreadings spectrophotometerpHmeters computer-assistedlabssaltbridge

InternetResourcesOnlinecontent that reinforces themajorconceptsdiscussed in thischaptercanbefoundatthefollowingInternetaddressesiftheyarestillavailable.Somemayhavebeenchangedordeleted.ChemistrySafetyRuleswww.science.fau.edu/chemistry/chemlab/General/safety.htmlThissitewebsitegivesagoodreviewoflaboratorysafetyrules.

PracticeExercises

1.Inthereactionsetupshownabove,whichofthefollowingaretrue?

I.Thissetupcanbeusedtoprepareasolublegasbywaterdisplacement.II.Thissetupinvolvesadecompositionreactionifthesubstanceheatedis

potassiumchlorate.III.Thissetupcanbeusedtoprepareaninsolublegasbywater

displacement.

(A)Ionly

(B)IIonly(C)IandIII(D)IIandIII(E)I,II,andIII

Questions2–4refertothefollowingdiagram:

(A)Aroundthethermometer(B)Inthecondenser(C)Inthecirculatingwater(D)Intheheatedflask(E)Inthedistillate

2.Inthislaboratorysetupfordistillation,wheredoesthevaporizationtakeplace?

3.Iftheliquidbeingdistilledcontainsdissolvedmagnesiumchloride,wherewillitbefoundafterdistillationiscompleted?

4.Iftheliquidbeingdistilledcontainsdissolvedammoniagas,wherewillitbeboundafterdistillationiscompleted?

________________________5.Iftheflameusedtoheataflaskisanorangecolorandblackensthebottomoftheflask,whatcorrectionshouldyoumaketosolvethisproblem?

(A)Movetheflaskfartherfromtheflame.

(B)Movetheflaskclosertotheflame.(C)Allowlessairintothecollaroftheburner.(D)Allowmoreairintothecollaroftheburner.(E)Theproblemisinthesupplyofthegas,andyoucannotfixit.

Questions6–8refertothefollowingdiagram:

6.Intheabovetitrationsetup,ifyouintroduce15mLoftheNaOHwithanunknownmolarityintotheflaskandthenadd5dropsofphenolphthaleinindicator,whatwillyouobserve?

(A)Apinkishcolorwillappearthroughoutthesolution.(B)Abluecolorwillappearthroughoutthesolution.(C)Therewillbeatemporarypinkishcolorthatwilldissipate.(D)Therewillbeatemporarybluecolorthatwilldissipate.(E)Therewillnotbeacolorchange.

7.IftheHClis0.1Mstandardsolutionandyoumustadd30mLtoreachtheendpoint,whatisthemolarityoftheNaOH?

(A)0.1M(B)0.2M(C)0.3M(D)1M

(E)2M

8.WhenistheendpointreachedandthevolumeoftheHClrecordedinthisreaction?

I.Whenthecolorfirstdisappearsandreturnsintheflask.II.WhenequalamountsofHClandNaOHareintheflask.III.Whenthecolordisappearsanddoesnotreturnintheflask.

(A)Ionly(B)IIIonly(C)IandIII(D)IIandIII(E)I,II,andIII

Questions9–11refertothefollowingdiagram:

Inthissetup,acleanstripofmagnesiumwithamassof0.040gwasintroducedinto the bottom of the tube, which contained a dilute solution of HCl, andallowed to react completely. The hydrogen gas formed was collected and thefollowingdatarecorded:

Airpressureintheroom=730mmHgTemperatureofthewatersolution=302KVaporpressureofwaterat302K=30.0mmHg

Thegascollecteddidnotfilltheeudiometer.Theheightofthemeniscusabovethelevelofthewaterwas40.8mm.

9.Whatisthetheoreticalyield(inmL)atSTPofhydrogengasproducedwhenthe0.040gofMgreactedcompletely?

(A)10mL(B)25mL(C)37mL(D)46mL(E)51mL

10.Whatisthecorrectiontotheatmosphericpressureduetothe40.8mmheightofthesolutioninthetubeandabovethelevelinthebeaker?

(A)3.0mmHg(B)6.0mmHg(C)13.6mmHg(D)27.2mmHg(E)40.8mmHg

11.Whatisthepressureofthecollectedgasonceyouhavealsocorrectedforthevaporpressureofthewater?

(A)730mmHg(B)727mmHg(C)30.0mmHg(D)697mmHg(E)760mmHg

Questions12–14

(A)Theruleistoaddconcentratedacidtowaterslowly.(B)Theruleistoaddwatertotheconcentratedacidslowly.(C)Carefullyreplaceunusedorexcesschemicalsintotheirproperly

labeledcontainersfromwhichtheycame.(D)Flusheyeswithwaterattheeyewashfountainforatleast15minutes,

andthenreporttheaccidentforfurtherhelp.(E)Disposeofchemicalsintheproperplacesandfollowingposted

procedures.Donotreturnthemtotheiroriginalcontainers.

12.Whichoftheabovechoicesistheproperwaytodiluteaconcentratedacid?

13.Howdoyouproperlydisposeofchemicalsnotneededintheexperiment?

14.Whatshouldyoudoifachemicalsplattersintoyoureye?

________________________15.Whatinstrumentisusedinchemistrylabstomeasurethemolarityofa

coloredsolutionbymeasuringthelighttransmittedthroughit?

(A)Electronicgravimetricbalance(B)pHmeter(C)Spectrophotometer(D)Computerassistedprobes(E)Galvanometer

AnswersandExplanations1.(D)Thissetupcanbeusedtoprepareaninsolublegasbutnotasolubleone.Ifthesubstanceispotassiumchlorate,itdoesdecomposeintopotassiumchlorideandoxygen.

2.(D)Vaporizationoccursintheheatedflask.

3.(D)Themagnesiumchloridewillbeleftbehindintheheatedflasksinceitisnotvolatileastheliquidboilsoff.

4.(E)Sincethedissolvedammoniaisvolatilebelowtheboilingpointofwater,itwillbefoundinthedistillate.Somewillalsoescapeasagas.

5.(D)Oneofthebasicadjustmentstoaburneristoassureenoughairismixingwiththegastoformabluecone-shapedflame.Withinsufficientair,carbondepositswillformontheflaskandtheflamewillbeorange.

6.(A)PhenolphthaleinindicatoriscolorlessbelowapHof8.3butisredtopinkinbasicsolutionsabovethispH.InthisNaOHsolution,itwillberedtopink.

7.(B)Calculatethemolaritybyusingtheformula:

Macid×Vacid=Mbase×Vbase0.1M×30mL=Mbase×15mL

Mbase=0.2M

Noticethataslongastheunitsofvolumearethesame,theycanceloutoftheequation.

8.(B)Theendpointisreachedwhenthecoloroftheindicatordisappearsanddoesnotreturn.Thecolorwillfirstdisappeartemporarilybeforetheendpointbutfinallywillnotreturn.

9.(C)ThetheoreticalyieldatSTPcanbefoundfromthechemicalequationofthereaction:

10.(A)The40.8mmofwaterbeingheldupinthetubebyatmosphericpressurecanbechangedtoitsequivalentheightofmercurybydividingby13.6,since1mmofHg=13.6mmofwater.

Bycorrectingtheatmosphericpressure,weget:730mmHg-3mmHg=727mmHg

11.(D)Correctingthepreviouspressurebysubtractingthegivenamountforthevaporpressureofwaterat302Kgivesyou727mmHg-30mmHgvaporpressure=697mmHgasthefinalpressure.

12.(A)Thecorrectandsafewaytodiluteconcentratedacidsistoaddwaterdownthesideofthebeakerslowlyandbeawareofanyheatbuildup.

13.(E)Youneverreturnchemicalsorsolutionstotheiroriginalcontainersforfearofcontaminatingtheoriginalsource.

14.(D)Itisessentialtogetyoureyeswashedofanychemicals.Knowwheretheeyewashfountainsare,andknowhowtousethem.

15.(C)Oneofthenewtechnologicaladditionstochemistrylabsisthespectron20thatusestheabsorptionoflightwavestodoqualitativeandquantitativeinvestigationsinthelab.

PART3

PRACTICETESTS

PracticeSubjectTestsinChemistry

TheSubjectTests inChemistryareplanned to test theprinciplesandconceptsdrawn from the factualmaterial found largely in inorganicchemistryand, toamuch lesser extent, in organic chemistry. Only a few questions are askedconcerningindustrialoranalyticalchemistry.Adetaileddescriptionofeveryaspectofthetestisgivenintheintroductionof

this book. Read it carefully. Study the types of questions asked on the test.Carefullyreadtheinstructionsgivenforeachtypeofquestionatthebeginningof each section. Note: The Practice Test questions contain hyperlinks to theiranswersandexplanations.Remembertoclickonthequestionnumberstomovebackandforth.You will be provided with a Periodic Table to use during the test. All

necessaryinformationregardingatomicnumbersandatomicmassesisgivenonthechart.Beforeyouattemptanyof thepractice tests, read the information intheIntroductionandthematerialthatprecedestheDiagnosticTestinthefrontofthisbook.Whenyouunderstandtheinformationthere,areawareofthetypesofquestionsandtheirrespectivedirections,andknowhowthetestwillbescored,youarereadytotakePracticeTest1.Rememberthatyouhave1hourandthatyoumaynotuseacalculator.Use

thePeriodicTable provided for theDiagnosticTest in the front of this book,andrecordyouranswersintheappropriatespacesontheanswersheet.Afteryouhave takeneach test, follow the instructions fordiagnosingyour strengthsandweaknessesandforhowtoimproveinthoseareas.

All PracticeAnswer Sheets are for reference only. Please record all ofyouranswersseparately.

AnswerSheetPRACTICETEST1

Determine the correct answer for each question. Then, using a No. 2pencil,blackencompletelytheovalcontainingtheletterofyourchoice.

PracticeTest1Note: For all questions involving solutions and/or chemical equations, assumethatthesystemisinwaterunlessotherwisestated.

Reminder:Youmaynotuseacalculatoronthesetests.Thefollowingsymbolshavethemeaningslistedunlessotherwisenoted.

H=enthalpy g=gram(s)M=molar J=joules(s)n=numberofmoles kJ=kilojoulesP=pressure L=liter(s)R=molargasconstant mL=milliliter(s)

S=entropy mm=millimeter(s)T=temperature mol=mole(s)V=volume V=volt(s)atm=atmosphere

PartA

Directions: Every set of the given lettered choices below refers to thenumberedstatementsorformulasimmediatelyfollowingit.Choosetheoneletteredchoicethatbestfitseachstatementorformulaandthenfill inthecorresponding oval on the answer sheet. Each choicemay be used once,morethanonce,ornotatallineachset.

Questions1–6refertothechoicesinthefollowingtable:

PeriodicTable(abbreviated)

1.Themostelectronegativeelement

2.Theelementwithapossibleoxidationnumberof–2

3.Theelementthatwouldreactina1:1ratiowith(D)

4.Theelementwiththesmallestionicradius

5.Theelementwiththesmallestfirstionizationpotential

6.Theelementwithacompleteporbitalasitsoutermostenergylevel

Questions7–9refertothefollowingterms.

(A)Reductionpotential(B)Ionizationenergy(C)Electronegativity(D)Heatofformation(E)Activationenergy

7.Thisistheenergychangethataccompaniesthecombiningofelementsintheirnaturalstatestoformacompound.

8.Thisistheenergyneededtoremoveanelectronfromagaseousatominitsgroundstate.

9.Thisistheminimumenergyneededformoleculestoreactandformcompounds.

Questions10–12refertothefollowingheatingcurveforwater:

10.InwhichpartofthecurveisthestateofH2Oonlyasolid?

11.Whichpartofthegraphshowsaphasechangerequiringthegreatestamountofenergy?

12.WhereisthetemperatureofH2Ochangingat4.18J/g°C(or1cal/g°C)?

Questions13–15refertothefollowingdiagram:

13.Indicatestheactivationenergyoftheforwardreaction

14.Indicatestheactivationenergyofthereversereaction

15.Indicatesthedifferencebetweentheactivationenergiesforthereverseandforwardreactionsandequalstheenergychangeinthereaction

Questions16–18refertothefollowingelementsinthegroundstate:

(A)Fe(B)Au(C)Na(D)Ar

(E)U

16.Acommonmetalelementthatresistsreactionwithacids

17.Amonoatomicelementwithfilledporbitals

18.Atransitionelementthatoccurswhentheinner3dorbitalispartiallyfilled

Questions19and20refertothefollowing:

(A)Radioactiveisotope(B)Monocliniccrystal(C)Sulfurtrioxide(D)Sulfatesalt(E)Allotropicform

19.Asubstancethatexhibitsaresonancestructure

20.AproductformedfromabasereactingwithH2SO4

Questions21–23refertothefollowingterms:

(A)Dilute(B)Concentrated(C)Unsaturated(D)Saturated(E)Supersaturated

21.Thecondition,unrelatedtoquantities,thatindicatesthattherategoingintosolutionisequaltotheratecomingoutofsolution

22.Theconditionthatexistswhenawatersolutionthathasbeenatequilibriumandsaturatedisheatedtoahighertemperaturewithahighersolubility,butnoadditionalsoluteisadded

23.Thedescriptivetermthatindicatesthereisalargequantityofsolute,comparedwiththeamountofsolvent,inasolution

PartB

ONTHEACTUALCHEMISTRYTEST,THEFOLLOWINGTYPEOFQUESTION MUST BE ANSWERED ON A SPECIAL SECTION(LABELED“CHEMISTRY”)ATTHELOWERLEFT-HANDCORNEROF YOUR ANSWER SHEET. THESE QUESTIONS WILL BENUMBERED BEGINNING WITH 101 AND MUST BE ANSWEREDACCORDINGTOTHEFOLLOWINGDIRECTIONS.

Directions: Every question below contains two statements, I in the left-handcolumnandIIintheright-handcolumn.Foreachquestion,decideifstatementIistrueorfalseandifstatementIIistrueorfalseandfillinthecorrespondingTorFovalsonyouranswersheet.*FillinovalCEonlyifstatementIIisacorrectexplanationofstatementI.

SampleAnswerGrid:

CHEMISTRY*FillinovalCEonlyifIIisacorrectexplanationofI.

I II101.Nonmetallicoxidesare

usuallyacidanhydridesBECAUSE nonmetallicoxidesformacids

whenplacedinwater.102.WhenHClgasandNH3gas

comeintocontact,awhitesmokeforms

BECAUSENH3andHClreacttoformawhitesolid,ammoniumchlorate.

103.Thereactionofbariumchlorideandsodiumsulfatedoesnotgotocompletion

BECAUSEthecompoundbariumsulfateisformedasaninsolubleprecipitate.

104.Whentwoelementsreactexothermicallytoformacompound,thecompoundshouldberelativelystable

BECAUSE

thereleaseofenergyfromacombinationreactionindicatesthatthecompoundformedisatalowerenergylevelthanthereactantsandthusrelativelystable.whenanonmetallicionis

105.Theionofanonmetallicatomislargerinradiusthantheatom

BECAUSEformed,itgainselectronsintheouterorbitalandthusincreasesthesizeoftheelectroncloudaroundthenucleus.

106.Oxidationandreductionoccurtogether

BECAUSE inredoxreactions,electronsmustbegainedandlost.

107.Decreasingtheatmosphericpressureonapotofboilingwatercausesthewatertostopboiling

BECAUSEchangesinpressurearedirectlyrelatedtotheboilingpointofwater.

108.Thereactionofhydrogenwithoxygentoformwaterisanexothermicreaction

BECAUSEwatermoleculeshavepolarcovalentbonds.

109.Atomsofdifferentelementscanhavethesamemassnumber

BECAUSEtheatomsofeachelementhaveacharacteristicnumberofprotonsinthenucleus.

110.Thetransmutationdecayofcanbeshownas BECAUSE

thetransmutationof isaccompaniedbythereleaseofabetaparticle.

111. and areisotopesoftheelementcarbon

BECAUSE

isotopesofanelementhavethesamenumberofprotonsinthenucleusbuthaveadifferentnumberofneutrons.

112.TheCu2+ionneedstobeoxidizedtoformCumetal

BECAUSE oxidationisagainofelectrons.

113.Thevolumeofagasat373Kandapressureof600millimetersofmercurywillbedecreasedatSTP

BECAUSE

decreasingthetemperatureandincreasingthepressurewillcausethevolumetodecreasebecause

114.ThepHofa0.01molarsolutionofHClis2

BECAUSE diluteHCldissociatesintotwoessentiallyionicparticles.

115.Nuclearfusiononthesunconvertshydrogentoheliumwithareleaseofenergy

BECAUSEsomemassisconvertedtoenergyinasolarfusion.

theradiusofanoxygenatomis

116.Thewatermoleculeispolar BECAUSE greaterthanthatofahydrogenatom.

PartC

Directions:Everyquestionor incompletestatementbelowis followedbyfivesuggestedanswersorcompletions.Choosetheonethatisbestineachcaseandthenfillinthecorrespondingovalontheanswersheet.

24.WhatistheapproximateformulamassofCa(NO3)2?

(A)70(B)82(C)102(D)150(E)164

25.Inthereaction2KClO3+MnO2+2KCl+3O2(g)+MnO2,whichsubstanceisthecatalyst?

(A)O2

(B)KClO3

(C)MnO2

(D)KCl(E)O2intheMnO2

26.Thenormalconfigurationforethyne(acetylene)is

(A)H—C C—H(B)H—C—C—H(C)H—CH2—CH2—H(D)H—C C—H(E)H—CH—CH—H

27.AccordingtotheKinetic-MolecularTheory,moleculesincreaseinkineticenergywhenthey

(A)aremixedwithothermoleculesatlowertemperature(B)arefrozenintoasolid(C)arecondensedintoaliquid(D)areheatedtoahighertemperature(E)collidewitheachotherinacontaineratalowertemperature

28.HowmanyatomsarerepresentedintheformulaCa3(PO4)2?

(A)5(B)8(C)9(D)12(E)13

29.AllofthefollowinghavecovalentbondsEXCEPT

(A)HCl(B)CCl4(C)H2O(D)CsF(E)CO2

30.Whichofthefollowingis(are)theWEAKESTattractiveforce?

(A)Dipole-dipoleforces(B)Coordinatecovalentbonding(C)Covalentbonding(D)Polarcovalentbonding(E)Ionicbonding

31.Whichoftheseresemblesthemolecularstructureofthewatermolecule?

(A)

(B)

(C)

(D)

(E)

32.Thetwomostimportantconsiderationsindecidingwhetherareactionwilloccurspontaneouslyare

(A)thestabilityandstateofthereactants(B)theenergygainedandtheheatevolved(C)anegativevalueforΔHandapositivevalueforΔS(D)apositivevalueforΔHandanegativevalueforΔS(E)theendothermicenergyandthestructureoftheproducts

33.ThereactionofanacidsuchasHClandabasesuchasNaOHalways

(A)formsaprecipitate(B)formsavolatileproduct(C)formsaninsolublesaltandwater(D)formsasulfatesaltandwater(E)formsasaltandwater

34.TheoxidationnumberofsulfurinH2SO4is

(A)+2(B)+3(C)+4(D)+6(E)+8

35.Balancethisredoxreactionbyusingthehalf-reactionmethodofelectronexchange:KMnO4+H2SO3→K2SO4+MnSO4+H2SO4+H2OWhichofthefollowingpartialequationsisthecorrectreductionhalf-reactionforthebalancedequation?

(A)5SO32−+5H2O→5SO4

2−+10H++10e−

(B)2MnO4−+16H++10e−→2Mn2++8H2O

(C)SO32−→SO4

2−+2e−

(D)SO32−+2H+→SO4

2−+H2O+2e−

(E)Mn7+→Mn2++5e−

36.Whichofthefollowingwhenplacedintowaterwilltestasanacidsolution?

I.HCl(g)+H2O

II.ExcessH3O++H2OIII.CuSO4(s)+H2O

(A)Ionly(B)IIIonly(C)IandIIonly(D)IIandIIIonly(E)I,II,andIII

37.Thepropertyofmatterthatisindependentofitssurroundingconditionsandpositionis

(A)volume(B)density(C)mass(D)weight(E)state

38.WherearethehighestionizationenergiesfoundinthePeriodicTable?

(A)Upperleftcorner(B)Lowerleftcorner(C)Upperrightcorner(D)Lowerrightcorner(E)Middleoftransitionelements

39.WhichofthefollowingpairsofcompoundscanbeusedtoillustratetheLawofMultipleProportions?

(A)NOandNO2

(B)CH4andCO2

(C)ZnO2andZnCl2(D)NH3andNH4Cl(E)H2OandHCl

40.Inthisequilibriumreaction:A+B AB+heat(inaclosedcontainer),howcouldtheforwardreactionratebeincreased?

I.ByincreasingtheconcentrationofABII.ByincreasingtheconcentrationofAIII.ByremovingsomeofproductAB

(A)Ionly(B)IIIonly(C)IandIIIonly(D)IIandIIIonly(E)I,II,andIII

41.Forthereactionofsodiumwithwater,thebalancedequationusingthesmallestwholenumbershaswhichofthefollowingcoefficients?

I.1II.2III.3

(A)Ionly(B)IIIonly(C)IandIIonly(D)IIandIIIonly(E)I,II,andIII

42.If10litersofCOgasreactwithsufficientoxygenforacompletereaction,howmanylitersofCO2gasareformed?

(A)5(B)10(C)15(D)20

(E)40

43.If49gramsofH2SO4reactwith80.0gramsofNaOH,howmuchreactantwillbeleftoverafterthereactioniscomplete?

(A)24.5gH2SO4

(B)noneofeithercompound(C)20.gNaOH(D)40.gNaOH(E)60.gNaOH

44.IfthemolarconcentrationofAg+ionsin1literofasaturatedwatersolutionofsilverchlorideis1.38×10−5mole/liter,whatistheKspofthissolution?

(A)0.34×10−10

(B)0.69×10−5

(C)1.90×10−10

(D)2.76×10−5

(E)2.76×10−10

45.IfthedensityofadiatomicgasatSTPis1.43grams/liter,whatisthegram-molecularmassofthegas?

(A)14.3g(B)32.0g(C)48.0g(D)64.3g(E)224g

46.From2molesofKClO3howmanylitersofO2canbeproducedatSTPbydecompositionofalltheKClO3?

(A)11.2(B)22.4(C)33.6(D)44.8(E)67.2

47.Whichvaluebestdetermineswhetherareactionisspontaneous?

(A)changeinGibbsfreeenergy,ΔG(B)changeinentropy,ΔS(C)changeinkineticenergy,ΔKE(D)changeinenthalpy,ΔH(E)changeinheatofformation,ΔH0f

Questions48–52refertothefollowingexperimentalsetupanddata:

Recordeddata:

Before:CuO+porcelainboat =62.869gCaCl2+U-tube =80.483g

After:Porcelainboat+contents =54.869gCaCl2+U-tube =89.483g

Reactions:Zn(s)+2HCl(aq)→ZnCl2(aq)+H2(g)thenH2(g)+CuO(s)→H2O(g)+Cu(s)

48.Whattypeofreactionoccurredintheporcelainboat?

(A)electrolysis(B)doubledisplacement(C)reductionandoxidation(D)decompositionoranalysis(E)combinationorsynthesis

49.WhywastheCaCl2tubeplacedbetweenthegeneratorandthetube

containingtheporcelainboat?

(A)ToabsorbevaporatedHCl(B)ToabsorbevaporatedH2O(C)Toslowdownthegasesreleased(D)ToabsorbtheevaporatedZnparticles(E)Toremovetheinitialairthatpassesthroughthetube

50.Howmanygramsofhydrogenwereusedintheformationofthewaterthatwasaproduct?

(A)1(B)2(C)4(D)8(E)9

51.Whatconclusioncanyoudrawfromthisexperiment?

(A)Hydrogendiffusesfasterthanoxygen.(B)Hydrogenislighterthanoxygen.(C)Themolarmassofoxygenis32g/mol.(D)Waterisatriatomicmoleculewithpolarcharacteristics.(E)Waterisformedfromhydrogenandoxygeninaratioof1:8,bymass.

52.Whichofthefollowingisanobservationratherthanaconclusion?

(A)Asubstanceisanacidifitchangeslitmuspaperfrombluetored.(B)Agasislighterthanairifitescapesfromabottleleftmouthupward.(C)ThegasH2formsanexplosivemixturewithair.(D)Airismixedwithhydrogengasandignited;itexplodes.(E)Aliquidoilisimmisciblewithwaterbecauseitseparatesintoalayer

abovethewater.

53.WhenHClfumesandNH3fumesareintroducedintooppositeendsofalong,dryglasstube,awhiteringformsinthetube.Whichstatementexplainsthisphenomenon?

(A)NH4Clforms.

(B)HCldiffusesfaster.(C)NH3diffusesfaster.(D)TheringoccursclosertotheendintowhichHClwasintroduced.(E)Theringoccursintheverymiddleofthetube.

54.Thecorrectformulaforcalciumhydrogensulfateis

(A)CaH2SO4

(B)CaHSO4

(C)Ca(HSO4)2(D)Ca2HSO4

(E)Ca2H2SO4

55.Fortygramsofsodiumhydroxideisdissolvedinenoughwatertomake1literofsolution.Whatisthemolarityofthesolution?

(A)0.25M(B)0.5M(C)1M(D)1.5M(E)4M

56.Forasaturatedsolutionofsaltinwater,whichstatementistrue?

(A)Alldissolvinghasstopped.(B)Crystalsbegintogrow.(C)Anequilibriumhasbeenestablished.(D)Crystalsofthesolutewillvisiblycontinuetodissolve.(E)Thesoluteisexceedingitssolubility.

57.Inwhichofthefollowingseriesisthepibondpresentinthebondingstructure?

I.AlkaneII.AlkeneIII.Alkyne

(A)Ionly(B)IIIonly

(C)IandIIIonly(D)IIandIIIonly(E)I,II,andIII

Questions58and59refertothefollowingsetup:

58.WhycouldyouNOTusethissetupforpreparingH2ifthegeneratorcontainedZn+vinegar?

(A)Hydrogenwouldnotbeproduced.(B)Thesetupofthegeneratorisimproper.(C)Thegeneratormustbeheatedwithaburner.(D)Thedeliverytubesetupiswrong.(E)Thegascannotbecollectedoverwater.

59.Inaproperlaboratorysetupforcollectingagasbywaterdisplacement,whichofthesegasescouldNOTbecollectedoverH2Obecauseofitssolubility?

(A)CO2

(B)NO(C)O2

(D)NH3

(E)CH4

60.WhatistheapproximatepercentageofoxygenintheformulamassofCa(NO3)2?

(A)28

(B)42(C)58(D)68(E)84

61.Forthefollowingreaction:N2O4(g) 2NO2(g),theKeqexpressionis

(A)

(B)

(C)

(D)

(E)

62.WhatistheKeqforthereactioninquestion61ifatequilibriumtheconcentrationofN2O4is4×10−2mole/literandthatofNO2is2×10−2

mole/liter?

(A)1×10−2

(B)2×10−2

(C)4×10−2

(D)4×10−4

(E)8×10−2

63.Howmuchwater,inliters,mustbeaddedto0.50literof6.0MHCltomakethesolution2.0M?

(A)0.33(B)0.50(C)1.0(D)1.5

(E)2.0

64.4.0gramsofhydrogenareignitedwith4.0gramsofoxygen.Howmanygramsofwatercanbeformed?

(A)0.50(B)2.5(C)4.5(D)8.0(E)36

65.Whichstructureisanester?

(A)

(B)

(C)

(D)

(E)

66.Whatpieceofapparatuscanbeusedtointroducemoreliquidintoareactionandalsoserveasapressurevalve?

(A)Stopcock(B)Pinchcock(C)Thistletube

(D)Flask(E)Condenser

67.Whichformulascouldrepresenttheempiricalformulaandthemolecularformulaofagivencompound?

(A)CH2OandC4H6O4

(B)CHOandC6H12O6

(C)CH4andC5H12

(D)CH2andC3H6

(E)COandCO2

68.ThereactionFe→Fe2++2e−(+0.44volt)wouldoccurspontaneouslywithwhichofthefollowing?

I.Pb→Pb2++2e−(+0.13volt)II.Cu→Cu2++2e−(-0.34volt)III.2Ag++2e−→2Ag0(+0.80volt)

(A)Ionly(B)IIIonly(C)IandIIIonly(D)IIandIIIonly(E)I,II,andIII

69.2Na(s)+Cl2(g)→2NaCl(s)+822kJHowmuchheatisreleasedbytheabovereactionif0.5moleofsodiumreactscompletelywithchlorine?

(A)205kJ(B)411kJ(C)822kJ(D)1,640kJ(E)3,290kJ

Ifyoufinishbeforeonehourisup,youmaygobacktocheckyourworkorcompleteunansweredquestions.

AnswerKeyPRACTICETEST1

1.D 14.B 104.T,T,CE2.C 15.C 105.T,T,CE3.B 16.B 106.T,T,CE4.A 17.D 107.F,T5.B 18.A 108.T,T6.E 19.C 109.T,T7.D 20.E 110.T,F8.B 21.D 111.T,T,CE9.E 22.C 112.F,F10.A 23.B 113.T,T,CE11.D 101.T,T,CE 114.T,T12.C 102.T,F 115.T,T,CE13.E 103.F,T 116.T,T

24.E 39.A 54.C25.C 40.D 55.C26.D 41.C 56.C27.D 42.B 57.D28.E 43.D 58.B29.D 44.C 59.D30.A 45.B 60.C31.D 46.E 61.D

32.C 47.A 62.A33.E 48.C 63.C34.D 49.B 64.C35.B 50.A 65.E36.E 51.E 66.C37.C 52.D 67.D38.C 53.A 68.E

69.A

ANSWERSEXPLAINED1.(D)Themostelectronegativeelement,F,wouldbefoundintheupperrightcornerofthetable;thenoblegasesareexceptionsatthefarright.

2.(C)Elementsinthegroupwith(C)haveapossibleoxidationnumberof–2.

3.(B)Elementsinthegroupwith(B)reactina1:1ratiowithelementsinthegroupwith(D),sinceonehasanelectrontoloseandtheotheroneneedsanelectrontocompleteitsouterenergylevel.

4.(A)(A)loses2electronstoformanionwhoseremainingelectrons,beingclosetothenucleus,arepulledincloserbecauseoftheunbalanced2+charge.

5.(B)Since(B)hasonlyoneelectronintheouter4sorbital,itcanmoreeasilyberemovedthancananelectronfromthe3sorbitalof(A),whichisclosertothepositivenucleus.

6.(E)AllGroupVIIIelementshaveacompleteporbitalastheouterenergylevel.Thisexplainswhytheseelementsare“inert.”

7.(D)Theheatofformationistheenergychangecausedbythedifferenceintheinitialenergyandfinalenergyofthesystemwhenelementsintheirstandardstatereacttoformacompound.

8.(B)Theionizationenergyisdefinedastheenergyneededtoremoveanelectronfromthegroundstateoftheisolatedgaseousatom(orion).

9.(E)Theactivationenergyisdefinedastheminimumenergyrequiredformoleculestoreact.Thisistrueforbothexothermicandendothermicreactions.

10.(A)H2OisiceinPartA.

11.(D)H2OchangesstateatPartsBandD.TheheatofvaporizationatD(540cal/gor2.26×103J/g)isgreaterthantheheatoffusion(80cal/gor3.34×102J/g)atB.

12.(C)Waterisheatingat1°C/cal/gor4.18J/g/1°CinPartC.

13.(E)Thisistheenergyneededtostarttheforwardreaction.

14.(B)ThepartindicatedbyBrepresentstheactivationenergyforthereversereaction.

15.(C)ThenetenergyreleasedistheendothermicquantityindicatedbyC.

16.(B)Goldisknownasacommonnoblemetalbecauseofitsresistancetoacids.Aquaregia,amixtureofHNO3andHCl,willreactwithgold.

17.(D)Argonistheonlyelementamongthechoicesthatismonoatomicinthegroundstate.

18.(A)Ironhas5electronsinthedorbitals,whicharepartiallyfilled.

19.(C)Onlysulfurtrioxidehasaresonancestructure(asshownhere):

20.(E)Sulfuricacidreactswithabasetoformasulfatesalt.

21.(D)Theconditiondescribedistheequilibriumthatexistsatsaturation.

22.(C)Withtheincreasedtemperaturemoresolutemaygointosolution;thereforethesolutionisnowunsaturated.

23.(B)Theterm“concentrated”meansthatthereisalargeamountofsoluteinthesolvent.

101.(T,T,CE)Nonmetallicoxidesareusuallyacidanhydrides,andtheyformacidsinwater.

102.(T,F)Thewhitesmokeformedisammoniumchloride,notammoniumchlorate.

103.(F,T)Thereactionofbariumchlorideandsodiumsulfatedoesgotocompletionsincebariumsulfateisaprecipitate.

104.(T,T,CE)Theproductofanexothermicreactionisrelativelystablebecauseitisatalowerenergylevelthanthereactants.

105.(T,T,CE)Bothstatementsaretrue,andthereasonexplainstheassertion.

106.(T,T,CE)Bothstatementsaretrue,andthereasonexplainstheassertion.

107.(F,T)Thestatementisfalsewhilethereasonistrue.Decreasingthepressureonaboilingpotwillonlycausethewatertoboilmorevigorously.

108.(T,T)Thestatementsaretrue,butthereasondoesn’texplaintheassertion.

109.(T,T)Thestatementsaretrue,butthereasondoesn’texplaintheassertion.

110.(T,F)Thetransmutationequationistrueandshowsthereleaseofanalphaparticle,notabetaparticle.

111.(T,T,CE)Thetwoconfigurationsofcarbonareisotopesbecausetheyhavethesameatomicnumberbutdifferentmassnumbersbecause has6protonsand7neutronswhile has6protonsand8neutrons.

112.(F,F)Boththestatementandthereasonarefalse.

113.(T,T,CE)Ingoingfrom100°Cto0°C,thevolumedecreasesasthegasgetscolder;therefore,thetemperaturefractionexpressedinkelvinsmustbetodecreasethevolume.Togofrom600mmto760mmofpressure

increasesthepressure,thuscausingthegastocontract.Thefractionmustthenbe tocausethevolumetodecrease.Youcouldusetheformula

114.(T,T)SinceHClisastrongacidandionizescompletelyindilutesolutionofwater(the[H+]and[H3O+]arethesamething),themolarconcentrationofa0.01molarsolutionis1×10−2mol/L.

pH=–log[H+]pH=–log[1×10–2]pH=–(–2)=2

ThepHis2,butthereason,althoughtrue,doesnotexplainthestatement.

115.(T,T,CE)Bothstatementsaretrue,andthereasonexplainstheassertion.

116.(T,T)Thewatermoleculeispolarbecauseitsmolecularstructurehasthemoreelectronegativeoxygenmoleculeattheoneendandthetwohydrogenmolecules105°apart.Thiscausestheoxygenendtobemorenegativelychargedthanthehydrogensideofthemolecule.Theradiusoftheoxygenatomisgreaterthanthatofahydrogenatom,butthathasnothingtodowiththepolarnatureofthewatermolecule.

24.(E)Thetotalformulamassis:

25.(C)Thecatalyst,bydefinition,isnotconsumedinthereactionandendsupinitsoriginalformasoneoftheproducts.Inthisreaction,thecatalystistheMnO2.

26.(D)TheethynemoleculeisthefirstmemberoftheacetyleneserieswithageneralformulaofCnH2n-2.ItcontainsatriplebondbetweenthetwoCatoms:H—C C—H.

27.(D)Heatingmoleculesincreasestheirkineticenergy.

28.(E)3Ca+2P+8O=13atoms.

29.(D)Cesiumandfluorinearefromthemostelectropositiveandelectronegativeportions,respectively,oftheperiodicchart,andthusformanionicbondbycesiumgivinganelectrontofluorinetoformtherespectiveions.

30.(A)Dipole-dipoleforcesareduetotheweakattractionofthenuclearpositivechargeofoneatomtothenegativeelectronfieldofanadjacentatom.Theyaremuchweakerthantheothersnamed.

31.(D)Themolecularstructureofwateristhatofapolarcovalentcompoundwiththehydrogens105°apart.

32.(C)Themostimportantconsiderationsforaspontaneousreactionare(1)thatthereactionisexothermicwithanegativeΔH,sothatoncestartedittendstocontinueonitsownbecauseoftheenergyreleased,and(2)thatthereactiontendstogotothehigheststateofrandomness,shownbyapositivevalueforΔS.

33.(E)NormalH+acidsandOH−basesformwaterandasalt(notnecessarilyasolublesalt).

34.(D)Everycompoundhasachargeof0.Husuallyhas+1,andOusuallyhas-2,so

35.(B)Inthebalancedequationthetwohalf-reactionsare:

5SO32−+5H2O→5SO4

2−+10H++10e−

2MnO4−+16H++10e−→2Mn2++8H2O

2KMnO4+5H2SO3→K2SO4+2MnSO4+2H2SO4+3H2O

36.(E)HClandH3O+giveacidsolutions,asdoesCuSO4(thesaltofaweakbaseandastrongacid)whenithydrolyzesinwater.I,II,andIIIarecorrect.

37.(C)Massisaconstantandisnotdependentonpositionorsurroundingconditions.

38.(C)Thecompleteouterenergylevelsofelectronsofthesmallestnoblegaseshavethehighestionizationpotential.

39.(A)OnlyNOandNO2fitthedefinitionoftheLawofMultipleProportions,inwhichonesubstancestaysthesameandtheothervariesinunitsofwholeintegers.

40.(D)Increasingtheconcentrationofoneorbothofthereactantsandremovingsomeoftheproductformedwouldcausetheforwardreactiontoincreaseinratetotrytoregaintheequilibriumcondition.IIandIIIarecorrect.

41.(C)IandIIarecorrect.Theequationis2Na+2H2O→2NaOH+H2(g).Thecoefficientsincludea1anda2.

42.(B)2CO+O2→2CO2indicates2volumesofCOreactwith1volumeofO2toform2volumesofCO2.Therefore,10LofCOform10LofCO2.

43.(D)H2SO4+2NaOH→2H2O+Na2SO4istheequationforthisreaction.1molH2SO4=98g.1molNaOH=40g.Then49gofH2SO4= molH2SO4.Theequationshowsthat1molofH2SO4reactswith2molofNaOHforaratioof1:2.Therefore, molofH2SO4reactswith1molofNaOHinthisreaction.Since1molofNaOHequals40.g,and80.gofNaOHisgiven,40.gofitwillremainafterthereactionhasgonetocompletion.

44.(C)Ksp=[Ag+][Cl−]=1.9×10−10.ThemolarconcentrationsofAg+andCl−are1.38×10−5mol/L,so

[Ag+][Cl−]=Ksp[1.38×10−5][1.38×10−5]=1.90×10−10

45.(B)If1.43gisthemassof1L,thenthemassof22.4L,whichisthegram-molecularvolumeofagasatSTP,willgivethegram-molecularmass.Then,22.4L×1.43g/L=32.0g,thegram-molecularmass.

46.(E)Theequationis:

2KClO3(s)→2KCl(s)+3O2(g)

Thisshowsthat2molofKClO3yields3molofO2.ThreemolesofO2=3×22.4L=67.2LofO2.

47.(A)Gibbsfreeenergycombinestheoverallenergychangesandtheentropychange.TheformulaisΔG=ΔH–TΔS.OnlyifΔGisnegativewillthereactionbespontaneousintheforwarddirection.

48.(C)TheCuOwasreducedwhiletheH2wasoxidized,formingH2O+Cu.Thereductionandoxidationreactionis:

CuO(s)+H2(g)→H2O(l)+Cu(s)

49.(B)ThepurposeofthisCaCl2tubeistoabsorbanywaterevaporatedfromthegenerator.Ifitwerenotpresent,somewatervaporwouldpassthroughtothefinaldryingtubeandcausetheweightofwatergainedtheretobelargerthanitshouldbefromthereactiononly.

50.(A)Since8gofO2waslostbytheCuO,theweightofwatergainedbytheUtubecamefrom8gofO2and1gofH2,tomake9gofwaterthatitabsorbed.

51.(E)Theweightratioofwateris1gofH2to8gofO2or1:8.Theotherstatementsaretruebutarenotconclusionsfromthisexperiment.

52.(D)Thisistheonlyobservationofthegroup.Alltheothersareconclusions.Rememberthatanobservationisonlywhatyousee,smell,taste,ormeasurewithapieceofequipment.

53.(A)Thephenomenonistheformationofthewhitering,whichisNH4Cl.AlthoughthedistancetraveledbyeachgascouldbemeasuredtoverifyGraham’sLawofGaseousDiffusion,thiswasnotasked.Therelationshipisthatthediffusionrateisinverselyproportionaltothesquarerootofthegas’smolecularweight.

54.(C)SinceCa2+andHSO4−combine,theformulaisCa(HSO4)2.

55.(C)NaOHis40g/mol.40gin1Lmakesa1Msolution.

56.(C)Asaturatedsolutionrepresentsaconditionwherethesoluteisgoingintosolutionasrapidlyassomesoluteiscomingoutofthesolution.

57.(D)IIandIIIarecorrectsincethedouble-bondedcarbonsinthealkeneandthetriple-bondedcarbonsinthealkyneserieshavepibonds.

58.(B)Thethistletubeisnotbelowtheleveloftheliquidinthegeneratorandthegaswouldescapeintotheair.(Vinegarisanacidandwouldproducehydrogen.)

59.(D)NH3isverysolubleandcouldnotbecollectedinthismanner.Allothersarenotsufficientlysolubletohamperthismethodofcollection.

60.(C)Theformula(mass)isthetotalof(Ca=)40+(2N=)28+(6O=)96,or164.Sinceoxygenis96amuof164total,thepercentageis96/164×100=58.5%.

61.(D)TheKeqexpressionconsistsoftheconcentration(s)oftheproductsoverthoseofthereactants,withthecoefficientsbecomingexponents:

62.(A)

63.(C)Indilutionproblems,theexpressionsM1×V1=M2×V2canbeused.Substituting(6.0M)(0.50L)=(2.0M)(xL)givesx=1.5Ltotalvolume.Sincetherewas0.50Ltobeginwith,anadditional1Lmustbeadded.

64.(C)Thereactionequationandinformationgivencanbesetuplikethis:

Given Given4.0g 4.0g xg2H2 + O2 → 2H2O4.0g 32g 36g

Studying this shows that the limiting element will be the 4 g of oxygensince4gofH2wouldrequire32gofO2.Thesolutionsetupis

65.(E)Thefunctionalgroupofanesteris .Thisappearsonlyin(E).

66.(C)Thethistletubeservesboththesepurposes.

67.(D)Theempiricalformulaisarepresentationoftheelementsintheirsimplestratio.Therefore,CH2isthesimplestratioofthemolecularformulaC3H6.

68.(E)I,II,andIIIwouldoccursincetheirreductionreactionswouldbe–0.13,+0.34,+0.80V,respectively.Thesenumbersaddedto+0.44VseparatelygiveapositiveE0forthereactionwithFe.

69.(A)Intheequation,2molofNarelease822kJofheat.Ifonly0.5molofNaisconsumed,onlyone-fourthasmuchheatwillbereleased: ×822=205kJ.

CALCULATINGYOURSCOREYourscoreonpracticeTest1cannowbecomputedmanually.Theactualtestisscoredbymachine,butthesamemethodisusedtoarriveattherawscore.Youget one point for each correct answer. For eachwrong answer, you lose one-fourthofapoint.Questionsthatyouomitorthathavemorethanoneanswerarenotcounted.Onyouranswersheetmarkallcorrectanswerswitha“C”andallincorrectanswerswithan“X”.

DeterminingYourRawTestScoreTotalthenumberofcorrectanswersyouhaverecordedonyouranswersheet.ItshouldbethesameasthetotalofallthenumbersyouplaceintheblockinthelowerleftcornerofeachareaoftheSubjectAreasummaryinthenextsection.

A.Enterthetotalnumberofcorrectanswershere:________Nowcountthenumberofwronganswersyourecordedonyouranswersheet.

B.Enterthetotalnumberofwronganswershere:________MultiplythenumberofwronganswersinBby0.25.

C.Enterthatproducthere:________SubtracttheresultinCfromthetotalnumberofrightanswersinA.

D.Entertheresultofyoursubtractionhere:________E.RoundtheresultinDtothenearestwholenumber:________.

Thisisyourrawtestscore.

ConversionofRawScorestoScaledScoresYour raw score is converted by the College Board into a scaled score. TheCollegeBoardscoresrangefrom200to800.ThisconversionisdonetoensurethatascoreearnedonanyeditionofaparticularSATSubjectTestinChemistryiscomparabletothesamescaledscoreearnedonanyothereditionofthesametest.Becausesomeeditionsofthetestsmaybeslightlyeasierormoredifficultthan others, scaled scores are adjusted so that they indicate the same level ofperformance regardless of the edition of the test taken and the ability of thegroup that takes it. Consequently, a specific raw score on one edition of a

particulartestwillnotnecessarilytranslatetothesamescaledscoreonanothereditionofthesametest.Becausethepracticetestsinthisbookhavenolargepopulationofscoreswith

whichtheycanbescaled,scaledscorescannotbedetermined.Results from previous SAT Chemistry tests appear to indicate that the

conversionofrawscorestoscaledscoresGENERALLYfollowsthispattern:

Note that this scale provides only a general idea of what a raw score maytranslateintoonascaledscorerangeof800–200.Scalingoneverytestisusuallyslightly different. Some students who had taken the SAT Subject Test inChemistry after using this book had reported that they have scored slightlyhigherontheSATtestthanonthepracticetestsinthisbook.Theyallreportedthatpreparingwellforthetestpaidoffinabetterscore!

DIAGNOSINGYOURNEEDSAftertakingPracticeTest1,checkyouranswersagainstthecorrectones.Thenfillinthechartbelow.Inthespaceundereachquestionnumber,placeacheckifyouansweredthat

questioncorrectly.

EXAMPLE:

Ifyouranswertoquestion5wascorrect,placeacheckintheappropriatebox.

Next, total the check marks for each section and insert the number in thedesignatedblock.Nowdo thearithmetic indicated, and insertyourpercent foreacharea.

*Thesubjectareashavebeenexpandedtoidentifyspecificareasinthetext.

*Thesubjectareashavebeenexpandedtoidentifyspecificareasinthetext.

AnswerSheetPRACTICETEST2

Determine the correct answer for each question. Then, using a No. 2pencil,blackencompletelytheovalcontainingtheletterofyourchoice.

PracticeTest2Note:For all questions involving solutions and/or chemical equations, assumethatthesystemisinwaterunlessotherwisestated.

Reminder:Youmaynotuseacalculatoronthesetests.Thefollowingsymbolshavethemeaningslistedunlessotherwisenoted.

H=enthalpy T=temperature L=liter(s)M=molar V=volume mL=milliliter(s)n=numberofmoles atm=atmosphere mm=millimeter(s)P=pressure g=gram(s) mol=mole(s)R=molargasconstant J=joules(s) V=volt(s)S=entropy kJ=kilojoules

PartA

Directions: Every set of the given lettered choices below refers to thenumberedstatementsorformulasimmediatelyfollowingit.Choosetheoneletteredchoicethatbestfitseachstatementorformulaandthenfill inthecorresponding oval on the answer sheet. Each choicemay be used once,morethanonce,ornotatallineachset.

Questions1–4refertothefollowingterms:

(A)LawofDefiniteComposition(B)Nuclearfusion(C)vanderWaalsforces(D)Graham’sLawofDiffusion(Effusion)(E)Triplepoint

1.Ataparticulartemperatureandpressure,threestatesofasubstancemaycoexist.

2.Thecombiningofnucleitoreleaseenergy.

3.Theratiooftherateofmovementofhydrogengascomparedwiththerateofoxygengasis4:1.

4.Themoleculesofnitrogenmonoxideandnitrogendioxidedifferbyamultipleofthemassofoneoxygen.

Questions5–7refertothefollowingdiagram:

5.The HofthereactiontoformCOfromC+O2

6.The HofthereactiontoformCO2fromCO+O2

7.The HofthereactiontoformCO2fromC+O2

Questions8–11

(A)Hydrogenbond(B)Ionicbond(C)Polarcovalentbond(D)Nonpolarcovalentbond(E)Metallicbond

8.Thetypeofbondbetweenatomsofpotassiumandchloridewhentheyformacrystalofpotassiumchloride

9.Thetypeofbondbetweentheatomsinanitrogenmolecule

10.ThetypeofbondbetweentheatomsinamoleculeofCO2(electronegativitydifference=1)

11.Thetypeofbondbetweentheatomsofcalciuminacrystalofcalcium

Questions12–14refertothefollowinggraphs:

12.Theslopeofvolumevs.pressureforagasatconstanttemperature

13.Theslopeofpressurevs.temperatureforagasatconstantvolume

14.Theslopeofvolumevs.temperatureforagasatconstantpressure

Questions15–18

(A)Least-reactivefamilyofelements(B)Alkalimetals(C)Halogenfamilyofelements(D)Noblegases(E)Familywhoseoxidesformacidsinwater

15.Theelementsthatmostactivelyreactwithwatertoreleasehydrogen

16.Theelementsleastlikelytobecomeinvolvedinchemicalreactions

17.Familythatcontainselementsinthecoloredgaseousstate,intheliquidstate,andwithmetallicproperties

18.GroupofnonmetallicelementscontainingNandP

Questions19–23

(A)1s(B)2s(C)3s(D)3p(E)3d

19.Containsuptotenelectrons

20.Containsonepairofelectronsinthegroundstateofthelithiumatom

21.Isexactlyone-halffilledinthegroundstateofthephosphorousatom

22.Containsthevalenceelectronsinthegroundstateofthemagnesiumatom

23.Containsafilledorbitalofelectronsinthegroundstateofhelium

PartB

ONTHEACTUALCHEMISTRYTEST,THEFOLLOWINGTYPEOFQUESTION MUST BE ANSWERED ON A SPECIAL SECTION(LABELED“CHEMISTRY”)ATTHELOWERLEFT-HANDCORNEROF YOUR ANSWER SHEET. THESE QUESTIONS WILL BENUMBERED BEGINNING WITH 101 AND MUST BE ANSWEREDACCORDINGTOTHEFOLLOWINGDIRECTIONS.

Directions:Every question below contains two statements, I in the left-handcolumnandIIintheright-handcolumn.Foreachquestion,decideifstatementIistrueorfalseandifstatementIIistrueorfalseandfillinthecorrespondingTorFovalsonyouranswersheet.*FillinovalCEonlyifstatementIIisacorrectexplanationofstatementI.

SampleAnswerGrid:

CHEMISTRY*FillinovalCEonlyifIIisacorrectexplanationofI.

I II

101.ThestructureofSO3isshownbyusingmorethanonestructuralformula

BECAUSE SO3isveryunstableandresonatesbetweenthesepossiblestructures.

102.

Whenthe Gofareactionatagiventemperatureisnegative,thereactionoccursspontaneously

BECAUSE when Gisnegative, Hisalsonegative.

103.OnemoleofCO2hasagreatermassthan1moleofH2O

BECAUSE themolecularmassofCO2isgreaterthanthemolecularmassofH2O.

104. Hydrosulfuricacidisoftenusedinqualitativetests

BECAUSE H2S(aq)reactswithmanymetallicionstogivecoloredprecipitates.

105. Crystalsofsodiumchloridegointosolutioninwaterasions

BECAUSE thesodiumionhasa1+chargeandthechlorideionhasa1−chargeandtheyarehydratedbythewatermolecules.

106.

Ifsomephosphoricacid,H3PO4,isaddedtotheequilibriummixturerepresentedbytheequationH3PO4+H2O↔PO4

3−

+H3O+,theconcentrationofH3O+decreases

BECAUSE theequilibriumconstantofareactionchangesastheconcentrationofthereactantschanges

107.

The Hreactionofaparticularreactioncanbearrivedatbythesummationofthe Hreactionvaluesoftwoormorereactionsthat,addedtogether,givetheHreactionoftheparticular

reaction

BECAUSE Hess’sLawconformstotheFirstLawofThermodynamics,whichstatesthatthetotalenergyoftheuniverseisaconstant.

108.

Inareactionthathasbothaforwardandareversereaction,A+B AB,whenonlyAandBareintroducedintoareactingvessel,theforwardreactionrateisthehighestatthebeginningandbeginstodecreasefromthatpointuntilequilibriumisreached

BECAUSE thereversereactiondoesnotbeginuntilequilibriumisreached.

109. Atequilibrium,theforwardreactionandreversereactionstop

BECAUSE atequilibrium,thereactantsandproductshavereachedtheequilibriumconcentrations.

110.Thehydridorbitalformofcarboninacetyleneisbelievedtobethespform

BECAUSE C2H2isalinearcompoundwithatriplebondbetweenthecarbons.

111.Theweakestofthebondsbetweenmoleculesarecoordinatecovalentbonds

BECAUSE

coordinatecovalentbondsrepresenttheweakattractiveforceoftheelectronsofonemoleculeforthepositivelycharged

nucleusofanother.

112. Asaturatedsolutionisnotnecessarilyconcentrated

BECAUSE diluteandconcentratedaretermsthatrelateonlytotherelativeamountofsolutedissolvedinthesolvent.

113.LithiumisthemostactivemetalinthefirstgroupofthePeriodicTable

BECAUSE lithiumhasonlyoneelectronintheouterenergylevel.

114. Theanionsmigratetothecathodeinanelectrolyticcell

BECAUSE positivelychargedionsareattractedtothenegativelychargedcathode.

115.Theatomicnumberofaneutralatomthathasamassof39andhas19electronsis19

BECAUSE thenumberofprotonsinaneutralatomisequaltothenumberofelectrons.

116.Foranelementwithanatomicnumberof17,themostprobableoxidationnumberis+1

BECAUSE theouterenergylevelofthehalogenfamilyhasatendencytoaddoneelectrontoitself.

PartC

Directions: Each of the questions or incomplete statements below isfollowedbyfivesuggestedanswersorcompletions.Select theone that isbest in each case and then fill in the corresponding oval on the answersheet.

24.AllofthefollowinginvolveachemicalchangeEXCEPT

(A)theformationofHClfromH2andCl2(B)thecolorchangewhenNOisexposedtoair(C)theformationofsteamfromburningH2andO2

(D)thesolidificationofvegetableoilatlowtemperatures(E)theodorofNH3whenNH4ClisrubbedtogetherwithCa(OH)2powder

25.Whenmostfuelsburn,theproductsincludecarbondioxideand

(A)hydrocarbons(B)hydrogen(C)water(D)hydroxide(E)hydrogenperoxide

26.Inthemetricsystem,theprefixkilo-means

(A)100

(B)10−1

(C)10−2

(D)102

(E)103

27.Howmanyatomsarein1moleofwater?

(A)3(B)54(C)6.02×1023

(D)2(6.02×1023)(E)3(6.02×1023)

28.Whichofthefollowingelementsnormallyexistasmonoatomicmolecules?

(A)Cl(B)H(C)O(D)N(E)He

29.TheshapeofaPCl3moleculeisdescribedas

(A)bent(B)trigonalplanar(C)linear(D)trigonalpyramidal(E)tetrahedral

30.Thecompletelossofanelectronofoneatomtoanotheratomwiththeconsequentformationofelectrostaticchargesisreferredtoas

(A)acovalentbond(B)apolarcovalentbond(C)anionicbond(D)acoordinatecovalentbond

(E)apibondbetweenporbitals

31.Intheelectrolysisofwater,thecathodereductionreactionis

(A)2H2O(l)+2e−→H2(g)+2OH−+O2(g)

(B)2H2O(l)→ O2(g)+2H++2e−

(C)2OH−+2e−→O2(g)+H2(g)

(D)2H++2e−→H2(g)

(E)2H2O(l)+4e−→O2(g)+2H2(g)

32.Whichofthefollowingradiationemissionshasnomass?

(A)Alphaparticle(B)Betaparticle(C)Proton(D)Neutron(E)Gammaray

33.Ifaradioactiveelementwithahalf-lifeof100yearsisfoundtohavetransmutatedsothatonly25%oftheoriginalsampleremains,whatistheage,inyears,ofthesample?

(A)25(B)50(C)100(D)200(E)400

34.WhatisthepHofanaceticacidsolutionifthe[H3O+]=1×10−4

mole/liter?

(A)1(B)2(C)3(D)4(E)5

35.Thepolarityofwaterisusefulinexplainingwhichofthefollowing?

I.ThesolutionprocessII.TheionizationprocessIII.Thehighconductivityofdistilledwater

(A)Ionly(B)IIonly(C)IandIIonly(D)IIandIIIonly(E)I,II,andIII

36.Whensulfurdioxideisbubbledthroughwater,thesolutionwillcontain

(A)sulfurousacid(B)sulfuricacid(C)hyposulfuricacid(D)persulfuricacid(E)anhydroussulfuricacid

37.FourgramsofhydrogengasatSTPcontain

(A)6.02×1023atoms(B)12.04×1023atoms(C)12.04×1046atoms(D)1.2×1023molecules(E)12.04×1023molecules

38.Analysisofagasgave:C=85.7%andH=14.3%.Iftheformulamassofthisgasis42atomicmassunits,whataretheempiricalformulaandthetrueformula?

(A)CH;C4H4

(B)CH2;C3H6

(C)CH3;C3H9

(D)C2H2;C3H6

(E)C2H4;C3H6

39.Whichfractionwouldbeusedtocorrectagivenvolumeofgasat300Ktoitsnewvolumewhenitisheatedto333Kandthepressureiskeptconstant?

40.Whatwouldbethepredictedfreezingpointofasolutionthathas684gramsofsucrose(1mol=342g)dissolvedin2,000gramsofwater?

(A)-1.86°Cor271.14K(B)-0.93°Cor272.07K(C)-1.39°Cor271.61K(D)-2.48°Cor270.52K(E)-3.72°Cor269.28K

41.WhatistheapproximatepHofa0.005MsolutionofH2SO4?

(A)1(B)2(C)5(D)9(E)13

42.HowmanygramsofNaOHareneededtomake100gramsofa5%solution?

(A)2(B)5(C)20(D)40(E)95

43.FortheHaberprocess:N2+3H2 2NH3+heat(atequilibrium),whichof

thefollowingstatementsconcerningthereactionrateis/aretrue?

I.Thereactiontotherightwillincreasewhenpressureisincreased.II.Thereactiontotherightwilldecreasewhenthetemperatureis

increased.III.ThereactiontotherightwilldecreasewhenNH3isremovedfromthe

chamber.

(A)Ionly(B)IIonly(C)IandIIonly(D)IIandIIIonly(E)I,II,andIII

44.Ifyoutitrate1.0MH2SO4solutionagainst50.millilitersof1.0MNaOHsolution,whatvolumeofH2SO4,inmilliliters,willbeneededforneutralization?

(A)10.(B)25.(C)40.(D)50.(E)100

45.HowmanygramsofCO2canbepreparedfrom150gramsofcalciumcarbonatereactingwithanexcessofhydrochloricacidsolution?

(A)11(B)22(C)33(D)44(E)66

Question46referstothefollowingdiagram:

46.Thediagramrepresentsasetupthatmaybeusedtoprepareandcollect

(A)NH3

(B)NO(C)H2

(D)SO3

(E)CO2

47.ThelabsetupshownabovewasusedforthegravimetricanalysisoftheempiricalformulaofMgO.InsynthesizingMgOfromaMgstripinthecrucible,whichofthefollowingisNOTtrue?

(A)TheinitialstripofMgshouldbecleaned.(B)Thelidofthecrucibleshouldfittightlytoexcludeoxygen.(C)TheheatingofthecoveredcrucibleshouldcontinueuntiltheMgis

fullyreacted.(D)Thecrucible,lid,andthecontentsshouldbecooledtoroom

temperaturebeforemeasuringtheirmass.(E)WhentheMgappearstobefullyreacted,thecruciblelidshouldbe

partiallyremovedandheatingcontinued.

Questions48–50refertothefollowingexperimentalsetupanddata:

Recordeddata:WeightofU-tube................................20.36gWeightofU-tubeandcalciumchloride

before...................................................39.32gWeightofU-tubeandcalciumchlorideafter...................................................

57.32gWeightofboatandcontents(copperoxide)

before...................................................30.23gWeightofboatandcontentsafter...................................................14.23gWeightofboat...................................................5.00g

48.WhatisthereasonforthefirstCaCl2dryingtube?

(A)Generatewater(B)Absorbhydrogen(C)Absorbwaterthatevaporatesfromtheflask(D)Decomposethewaterfromtheflask(E)Actasacatalystforthecombinationofhydrogenandoxygen

49.Whatconclusioncanbederivedfromthedatacollected?

(A)OxygenwaslostfromtheCaCl2.(B)OxygenwasgeneratedintheU-tube.(C)Waterwasformedfromthereaction.(D)HydrogenwasabsorbedbytheCaCl2.(E)CuOwasformedinthedecomposition.

50.Whatistheratioofthemassofwaterformedtothemassofhydrogenusedintheformationofwater?

(A)1:8(B)1:9(C)8:1(D)9:1(E)8:9

51.Whatisthemass,ingrams,of1moleofKAl(SO4)2·12H2O?

(A)132(B)180(C)394(D)474(E)516

52.Whatmassofaluminumwillbecompletelyoxidizedby2molesofoxygenatSTP?

(A)18g(B)37.8g(C)50.4g(D)72.0g(E)100.8g

53.Ingeneral,whenmetaloxidesreactwithwater,theyformsolutionsthatare

(A)acidic(B)basic(C)neutral(D)unstable(E)colored

Questions54–56refertothefollowingdiagram:

54.Theoxidationreactionwilloccurat

(A)A(B)B(C)C(D)D(E)E

55.TheapparatusatCiscalledthe

(A)anode(B)cathode(C)saltbridge(D)ionbridge(E)osmoticbridge

56.Thestandardpotentialsofthemetalsare:

Zn2++2e−→Zn0E0=−0.76voltCu0→Cu2++2e−E0=−0.34volt

Whatwillbethevoltmeterreadingforthisreaction?

(A)+1.10(B)−1.10(C)+0.42(D)−0.42(E)−1.52

________________________

57.Howmanylitersofoxygen(STP)canbepreparedfromthedecompositionof212gramsofsodiumchlorate(1mol=106g)?

(A)11.2(B)22.4(C)44.8(D)67.2(E)78.4

58.Inthisequation:Al(OH)3+H2SO4→Al2(SO4)3+H2O,thewhole-numbercoefficientsofthebalancedequationare

(A)1,3,1,2(B)2,3,2,6(C)2,3,1,6(D)2,6,1,3(E)1,3,1,6

59.Whatis Hreactionforthedecompositionof1moleofsodiumchlorate?(Hf0values:NaClO3(s)=−85.7kcal/mol,NaCl(s)=−98.2kcal/mol,O2(g)=0kcal/mol)

(A)−183.9kcal(B)−91.9kcal(C)+45.3kcal(D)+22.5kcal(E)−12.5kcal

60.Isotopesofanelementarerelatedbecausewhichofthefollowingis(are)thesameintheseisotopes?

I.AtomicmassII.AtomicnumberIII.Arrangementoforbitalelectrons

(A)Ionly(B)IIonly(C)IandIIonly(D)IIandIIIonly(E)I,II,andIII

61.InthereactionofzincwithdiluteHCltoformH2,whichofthefollowing

willincreasethereactionrate?

I.IncreasingthetemperatureII.IncreasingtheexposedsurfaceofzincIII.UsingamoreconcentratedsolutionofHCl

(A)Ionly(B)IIonly(C)IandIIIonly(D)IIandIIIonly(E)I,II,andIII

62.Thelaboratorysetupshownabovecanbeusedtopreparea

(A)gaslighterthanairandsolubleinwater(B)gasheavierthanairandsolubleinwater(C)gassolubleinwaterthatreactswithwater(D)gasinsolubleinwater(E)gasthatreactswithwater

63.Inthisreaction:CaCO3+2HCl→CaCl2+H2O+CO2.If4.0molesofHClareavailabletothereactionwithanunlimitedsupplyofCaCO3,howmanymolesofCO2canbeproducedatSTP?

(A)1.0(B)1.5(C)2.0(D)2.5(E)3.0

64.AsaturatedsolutionofBaSO4at25°Ccontains3.9×10−5mole/literof

Ba2+ions.WhatistheKspofthissalt?

(A)3.9×10−5

(B)3.9×10−6

(C)2.1×10−7

(D)1.5×10−8

(E)1.5×10−9

65.If0.1moleofK2SO4wasaddedtothesolutioninquestion64,whatwouldhappentotheBa2+concentration?

(A)Itwouldincrease.(B)Itwoulddecrease.(C)Itwouldremainthesame.(D)Itwouldfirstincrease,thendecrease.(E)Itwouldfirstdecrease,thenincrease.

66.Whichofthefollowingwilldefinitelycausethevolumeofagastoincrease?

I.Decreasingthepressurewiththetemperatureheldconstant.II.Increasingthepressurewithatemperaturedecrease.III.Increasingthetemperaturewithapressureincrease.

(A)Ionly(B)IIonly(C)IandIIIonly(D)IIandIIIonly(E)I,II,andIII

67.Thenumberofoxygenatomsin0.50moleofAl2(CO3)3is

(A)4.5×1023

(B)9.0×1023

(C)3.6×1024

(D)2.7×1024

(E)5.4×1024

Question68referstoasolutionof1Macid,HA,withKa=1×10−6.

68.WhatistheH3O+concentration?(Assume[HA]=1,[H3O+]=x,[A−]=x.)

(A)1×10−5

(B)1×10−4

(C)1×10−2

(D)1×10−3

(E)0.9×10−3

________________________69.Whatisthepercentdissociationofaceticacidina0.1Msolutionifthe

[H3O+]is1×10−3mole/liter?

(A)0.01%(B)0.1%(C)1.0%(D)1.5%(E)2.0%

Ifyoufinishbeforeonehourisup,youmaygobacktocheckyourworkorcompleteunansweredquestions.

AnswerKeyPRACTICETEST2

1.E 14.C 104.T,T,CE2.B 15.B 105.T,T,CE

3.D 16.D 106.F,F4.A 17.C 107.T,T,CE5.B 18.E 108.T,F6.C 19.E 109.F,T7.A 20.A 110.T,T,CE8.B 21.D 111.F,F9.D 22.C 112.T,T,CE10.C 23.A 113.F,T11.E 101.T,F 114.F,T12.E 102.T,F 115.T,T,CE13.A 103.T,T,CE 116.F,T

24.D 39.E 54.A25.C 40.A 55.C26.E 41.B 56.A27.E 42.B 57.D28.E 43.C 58.C29.D 44.B 59.E30.C 45.E 60.D31.D 46.E 61.E32.E 47.B 62.D33.D 48.C 63.C34.D 49.C 64.E35.C 50.D 65.B36.A 51.D 66.A37.E 52.D 67.D38.B 53.B 68.D

69.C

ANSWERSEXPLAINED

1.(E)Aphasediagramshowsthatallthreestatescanexistatthetriplepoint.

2.(B)Thecombiningofnucleiiscallednuclearfusion.

3.(D)AccordingtoGraham’sLawofGaseousDiffusion(orEffusion),therateofdiffusionisinverselyproportionaltothesquarerootofthemolecularweight.

Then

4.(A)TheLawofDefiniteCompositionstatesthat,whencompoundsform,theyalwaysforminthesameratiobymass.Water,forinstance,alwaysformsinaratioof1:8ofhydrogentooxygenbymass.Fornitrogenmonoxide(NO)andnitrogendioxide(NO2)thedifferenceinmolecularmassisoneatomicmassofoxygen.

5.(B)Thefirststepisthe HforC+ O2→CO.Itreleases-110.5kJof12heat.Thisiswrittenas-110.5kJbecauseitisexothermic.

6.(C)Thisisthesecondsteponthediagram.Itreleases-283.0kJofheat.

7.(A)Toarriveatthe H,takethetotaldrop(−393.5kJ)oraddthesereactions:

8.(B)Potassiumandchlorinehavealargeenoughdifferenceintheirelectronegativitiestoformionicbonds.Therespectivepositionsofthesetwoelementsintheperiodicchartalsoareindicativeofthelargedifferenceintheirelectronegativityvalues.

9.(D)Twoatomsofanelementthatformsadiatomicmoleculealwayshaveanonpolarcovalentbondbetweenthemsincetheelectronattractionorelectronegativityofthetwoatomsisthesame.

10.(C)Electronegativitydifferencesbetween0.5and1.7areusuallyindicativeofpolarcovalentbonding.CO2isaninterestingexampleofanonpolarmoleculewithpolarcovalentbondssincethebondsaresymmetricalinthemolecule.

11.(E)Calciumisametalandformsametallicbondbetweenatoms.

12.(E)Thisgraphshowsthevolumedecreasingasthepressureisincreasedandthetemperatureisheldconstant.ItisanexampleofCharles’sLaw(V/T=k).

13.(A)Thisgraphshowsthepressureincreasingasthetemperatureisincreasedandthevolumeisheldconstant.ItisanexampleofGay-Lussac’sLaw(P/T=k).

14.(C)Thisgraphshowsthevolumeincreasingasthetemperatureisincreasedandthepressureisheldconstant.ItisanexampleofBoyle’sLaw(PV=k).

15.(B)Thealkalimetalsreactwithwatertoformhydroxidesandreleasehydrogen.Atypicalreactionis:

2Na(s)+2H2O( )→2NaOH(aq)+H2(g)

16.(D)Thenoblegasesaretheleastreactivebecauseoftheircompletedouterorbital.

17.(C)Thehalogenfamilycontainsthecoloredgasesfluorineandchlorineatroomtemperatures,thereddishliquidbromine,andmetallic-likepurpleiodine.

18.(E)Thesenonmetals,whentheyareoxides,reactasacidicanhydrideswithwatertoformacidsolutions.

19.(E)Thefive3dorbitalscancontainatotaloftenelectrons.

20.(A)The1sorbitalisfilledwithtwoelectronsinthelithiumatom.

21.(D)Thephosphorousatomhasahalf-filled3porbitallevel.

22.(C)The3sorbitalcontainsthevalenceelectronsofmagnesium.

23.(A)Theheliumatomhasafilled1sorbital.

101.(T,F)Sulfurtrioxideisshownbythreestructuralformulasbecauseeachbondis“hybrid”ofasingleanddoublebond.Resonanceinchemistrydoesnotmeanthatthebondsresonatebetweenthestructuresshowninthestructuraldrawing.

102.(T,F)When GisnegativeintheGibbsequation,thereactionisspontaneous.However,thetotalequationdeterminesthis,notjustthe H.TheGibbsequationis:

G= H−T S.

103.(T,T,CE)Onemoleofeachofthegasescontains6.02×1023molecules,buttheirmolecularmassesaredifferent.CO2isfoundbyaddingoneC=12andtwoO=32,oratotalof44amu.TheH2O,however,addsuptotwoH=2plusoneO=16,oratotalof18amu.Thusitistruethat1molofCO2at44g/molisheavierthan1molofH2Oat18g/mol.

104.(T,T,CE)Hydrosulfuricacidisaweakacidbutisusedinqualitativetestsbecauseofthedistinctlycoloredprecipitatesofsulfidesthatitformswithmanymetallicions.

105.(T,T,CE)Sodiumchlorideisanioniccrystal,notamolecule,anditsionsarehydratedbythepolarwatermolecules.

106.(F,F)TheadditionofmoreH3PO4causestheequilibriumtoshifttotherightandincreasetheconcentrationofH3O+ionsuntilequilibriumisrestored.Thereforethefirststatementisfalse.Thesecondisalsofalsesincetheequilibriumconstantremainsthesameatagiventemperature.

107.(T,T,CE)Thestatementistrue,andthereasonisalsotrueandexplainsthestatement.

108.(T,F)Thestatementistrue,butnotthereason.Inanequilibriumreaction,concentrationscanbeshowntoprogresslikethis:

untilequilibriumisreached.Thentheconcentrationsstabilize.

109.(F,T)Theforwardandreversereactionsareoccurringatequalrateswhenequilibriumisreached.Thereactionsdonotstop.Theconcentrationsremainthesameatthispoint.

110.(T,T,CE)Sinceacetyleneisknowntobealinearmoleculewithatriplebondbetweenthetwocarbons,thesporbitalsalongthecentralaxiswiththehydrogensbondedoneitherendfittheexperimentalevidence.

111.(F,F)TheweakestbondsbetweenmoleculesarevanderWaalsforces,notcoordinatecovalentbonds.

112.(T,T,CE)Thetermsdiluteandconcentratedmerelyindicatearelativelylargeamountofsolventandasmallamountofsolvent,respectively.Youcanhaveadilutesaturatedsolutionifthesoluteisonlyslightlysoluble.

113.(F,T)Cs,notLi,isthemostactiveGroupImetalbecauseCshas(a)thelargestatomicradius,thusmakingiteasiertoloseitsouterenergylevelelectron,and(b)theintermediateelectronshelpscreenthepositiveattractionofthenucleus,alsoincreasingtheeasewithwhichtheouterelectronislost.

114.(F,T)Thecationsarepositivelychargedionsandmigratetothecathode,whiletheanionsarenegativelychargedandmigratetotheanode.

115.(T,T,CE)Thereareasmanyelectronsasthereareprotonsinaneutralatom,andtheatomicnumberrepresentsthenumberofeach.

116.(F,T)Thefirsttwoprincipalenergylevelsfillupat2and8electrons,respectively.Thatleaves7electronstofillthe3sand3porbitalslikethis:3s2,3p5.Withonlyoneelectronmissinginthe3porbitals,themostlikelyoxidationnumberis−1.

24.(D)Thesolidificationofvegetableoilismerelyaphysicalchange,liketheformationoficefromliquidwateratlowertemperatures.Alltheotherchoicesinvolveactualrecombinationsofatomsandthusarechemicalchanges.

25.(C)Waterisformedbecausemostcommonfuelscontainhydrogenintheirstructures.

26.(E)Theotherchoices,inorder,represent1, ordeci-, orcenti-,and100orhect-.

27.(E)Onemoleofanysubstancecontains6.02×1023molecules.Sinceeachwatermoleculeistriatomic,therewouldbe3(6.02×1023)atomspresent.

28.(E)Thenoblegasesareallmonoatomicbecauseoftheircompleteouterenergylevels.Aruletohelpyourememberdiatomicgasesis:Gasesendingin-genor-ineusuallyformdiatomicmolecules.

29.(D)ByboththeVSEPR(valenceshellelectronpairrepulsion)methodandtheorbitalstructuremethod,thePCl3moleculeistrigonalpyramidal:

30.(C)Thecompletelossandgainofelectronsisanionicbond.Allotherbondsindicatedare“sharingofelectrons”typebondsorsomeformofcovalentbonding.

31.(D)ThecathodereactionreleasesonlyH2gas.Thishalf-reactionisasgivenin(D).

32.(E)Thebetaparticleisahigh-speedelectronandhasthesmallestmassofthefirstfourchoices.However,gammaraysareelectromagneticwaves.Theyhavenomass.

33.(D)If25%ofthesamplenowremains,then100yearsago50%wouldbepresent.Ifyougobackanother100years,thesamplewouldcontain100%oftheradioactiveelement.Therefore,thesampleis100+100=200yearsold.

34.(D)pH=−log[H3O+]=−log[1×10−4]=−(−4)=4.

35.(C)OnlyIandIIaretrue.Distilledwaterdoesnotsignificantlyconductanelectriccurrent.Thepolarityofthewatermoleculeishelpfulinionizationandincausingsubstancestogointosolution.

36.(A)SO2istheacidanhydrideofH2SO3orsulfurousacid.H2O+SO2→H2SO3.

37.(E)FourgramsofhydrogengasatSTPrepresent2molofhydrogensince2gisthegram-molecularmassofhydrogen.Eachmoleofagascontains6.02×1023molecules,so2molcontains2×6.02×1023or12.04×1023molecules.

38.(B)Tosolvepercentcompositionproblems,firstdividethe%givenbytheatomicmass:

Thendividebythesmallestquotienttogetsmallwholenumbers:

The empirical formula is CH2. Since the molecular mass is 42 and theempiricalformulahasamolecularmassof14,thetrueformulamustbe3timestheempiricalformula,orC3H6.

39.(E)Becausethetemperature(inkelvins)increasesfrom303Kto333K,thevolumeofthegasshouldincreasewithpressureheldconstant.Thecorrectfractionis .

40.(A)Onemoleofdissolvedsubstance(whichdoesnotionize)causesa1.86°Cdropinthefreezingpointofa1molalsolution.Since2,000gofwaterwereused,thesolutionhas or2molin2,000gofwater.Then

Thefreezingpointisdepressed1×−1.86°=−1.86°Cor271.14K.

41.(B)ThepHis−log[H+].A0.005molarsolutionofH2SO4ionizesinadilutesolutiontoreleasetwoH+ionspermoleculeofH2SO4.ThereforethemolarconcentrationofH+ionis2×0.005mol/Lor0.010mol/L.Substitutingthisintheformula,youhave:

pH=−log[0.01]=−log[1×10−2]The log of a number is the exponent to which the base 10 is raised toexpressthatnumberinexponentialform:

−log[1×10−2]=−[−2]=2

42.(B)Ifthesolutionistobe5%sodiumhydroxide,then5%of100gis5g.Percentisalwaysbymassunlessotherwisespecified.

43.(C)Becausethisequationisexothermic,highertemperatureswilldecreasethereactiontotherightandincreasethereactiontotheleft,soIIistrue.

Also,Iistruebecausewithanincreaseofpressurethereactionwilltrytorelievethatpressurebygoinginthedirectionthathastheleastvolume:inthisreaction, to theright.StatementIII isfalsebecauseremovingproductinthisreactionwouldincreasetheforwardreaction.StatementsIandIIaretrue.

44.(B)Thereactionis:

1molacid= (mol)ofbaseSincemolarity×volume(L)=moles,then

MaVa= MbVb(1.0M)(xL)= (1M)(0.05L)

xL= (0.05L)xL=0.025Lor25.mL

45.(E)Thereactionis:

150gCaCO3(s)+2HCl(aq)→CaCl2(aq)+H2O(l)+CO2(g)Thegram-molecularmassofcalciumis100g.Then150g= or1.5molofcalciumcarbonate.Accordingtotheequation,1molofCaCO3yields1molofcarbondioxide,so1.5molofCaCO3yields1.5molofCO2.Thegram-molecularmassofCO2=44g:1.5molofCO2=1.5×44g=66gCO2

46.(E)Theotherchoicesarewrongbecause:

(A)islighterthanair(B)reactswithair(C)islighterthanair(D)needsheattobeevolved

47.(B)TheMgneedsoxygentoformMgO;sothelidcannotbetightlysealed.OxygenisneededfortheMgtooxidizetoMgO.Allotherchoicesaretrue.

48.(C)ToensurethatallthewatervaporcollectedintheU-tubecomesfromthereaction,thefirstdryingtubeisplacedinthepathofthehydrogentoabsorbanyevaporatedwater.

49.(C)Calciumchlorideisdeliquescent,anditsweightgainofwaterindicatesthatwaterwasformedfromthereaction.

50.

Theratioofmassofwatertomassofhydrogenis18:2or9:1.

51.(D)1K=39,1Al=27,2(SO4)=2(32+16×4)=192,and12H2O=12(2+16)=216.Thistotals474g.

52.(D)

Or,usingthemolemethod:44.8L=2mol

Thisshowsthat:

SincemolarmassofAl=27/mol

53.(B)Metaloxidesaregenerallybasicanhydrides.

54.(A)SinceAistheanode,theoxidation(orlossofelectrons)willoccuronthispole.

55.(C)“Saltbridge”isthecorrectterminology.

56.(A)Zn→Zn2++e−E°=+0.76V

Cu2++2e−→Cu°E°=+0.34V

Totalis=+1.10V

(NoticethattheZnisbeingoxidizedandtheCu2+isbeingreduced.)Voltmeterwillread+1.10V.

57.(D)

Equationshows2mol→3molO23mol×22.4L/mol=67.2L

58.(C)Thebalancedequationhasthecoefficients2,3,1,and6:2Al(OH)3+3H2SO4→Al2(SO4)3+6H2O.

59.(E)ThereactionisNaClO3(s)→NaCl(s)+ O2(g).Hreaction= Hf(products)− Hf(reactants)Hreaction=(−98.2+0)−(−85.7)Hreaction=−12.5kcal

60.(D)IIandIIIareidentical;isotopesdifferonlyinthenumberofneutronsinthenucleusandthisaffectstheatomicmassonly.

61.(E)I,II,andIIIwillincreasetherateofthisreaction.Eachofthemcausestherateofthisreactiontoincrease.

62.(D)Thissetupdependsonwaterdisplacementofaninsolublegas.

63.(C)Thecoefficientsgivethemolarrelations,so2.0molofHClgiveoff1.0molofCO2.Given4.0molofHCl,youhave

64.(E)Ksp=[Ba2+][SO42−]since[Ba2+]isgivenas[3.9×10−5],andthe

equationBaSO4→Ba2++SO42−showstherewillbeasmanySO4

2−ionsasBa2+ions,thenboth[Ba2+]and[SO4

2−willequal3.9×10−5.So,Ksp=[3.9×10−5][3.9×10−5]Ksp=1.5×10−9

65.(B)Theintroductionofthe“commonion”SO42−at0.1molarforcesthe

equilibriumtoshifttotheleftandreducetheBa2+concentration.

66.(A)Accordingtothegaslaws,onlyIwillcauseanincreaseinthevolumeofaconfinedgas.

67.(D)In1molofAl2(CO3)3,nineoxygens(threecarbonateswiththreeoxygenatomseach)areineachmolecule,or9molofOatomsarein1molofAl2(CO3)3.Becauseonly0.50molisgiven,thereare (9)or4.5molofOatoms.In4.5molofoxygen,thereare

27.0×1023atomsor2.7×1024atoms.

68.(D)WhenHAionizes,itformsequalamountsofH+andA−ions,buttheseamountsareverysmallbecausetheKaisverysmall.Kacanbeexpressedas[H+][A−]/[HA].Becauseyouaretoldtoassume[HA]=1,youhave:

69.(C)Percentdissociation=

CALCULATINGYOURSCOREYourscoreonPracticeTest2cannowbecomputedmanually.Theactualtestisscoredbymachine,butthesamemethodisusedtoarriveattherawscore.Youget one point for each correct answer. For eachwrong answer, you lose one-fourthofapoint.Questionsthatyouomitorthathavemorethanoneanswerarenotcounted.Onyouranswersheetmarkallcorrectanswerswitha“C”andallincorrectanswerswithan“X”.

DeterminingYourRawTestScoreTotalthenumberofcorrectanswersyouhaverecordedonyouranswersheet.ItshouldbethesameasthetotalofallthenumbersyouplaceintheblockinthelowerleftcornerofeachareaoftheSubjectAreasummaryinthenextsection.

A.Enterthetotalnumberofcorrectanswershere:________Nowcountthenumberofwronganswersyourecordedonyouranswersheet.

B.Enterthetotalnumberofwronganswershere:________MultiplythenumberofwronganswersinBby0.25.

C.Enterthatproducthere:________SubtracttheresultinCfromthetotalnumberofrightanswersinA.

D.Entertheresultofyoursubtractionhere:________

E.RoundtheresultinDtothenearestwholenumber:________.Thisisyourrawtestscore.

ConversionofRawScorestoScaledScoresYour raw score is converted by the College Board into a scaled score. TheCollegeBoardscoresrangefrom200to800.ThisconversionisdonetoensurethatascoreearnedonanyeditionofaparticularSATSubjectTestinChemistryiscomparabletothesamescaledscoreearnedonanyothereditionofthesametest.Becausesomeeditionsofthetestsmaybeslightlyeasierormoredifficultthan others, scaled scores are adjusted so that they indicate the same level of

performance regardless of the edition of the test taken and the ability of thegroup that takes it. Consequently, a specific raw score on one edition of aparticulartestwillnotnecessarilytranslatetothesamescaledscoreonanothereditionofthesametest.Becausethepracticetestsinthisbookhavenolargepopulationofscoreswith

whichtheycanbescaled,scaledscorescannotbedetermined.Results from previous SAT Chemistry tests appear to indicate that the

conversionofrawscorestoscaledscoresGENERALLYfollowsthispattern:

Note that this scale provides only a general idea of what a raw score maytranslateintoonascaledscorerangeof800–200.Scalingoneverytestisusuallyslightly different. Some students who had taken the SAT Subject Test inChemistry after using this book had reported that they have scored slightlyhigherontheSATtestthanonthepracticetestsinthisbook.Theyallreportedthatpreparingwellforthetestpaidoffinabetterscore!

DIAGNOSINGYOURNEEDSAftertakingPracticeTest2,checkyouranswersagainstthecorrectones.Thenfillinthechartbelow.Inthespaceundereachquestionnumber,placeacheckifyouansweredthat

questioncorrectly.

EXAMPLE:

Ifyouranswertoquestion5wascorrect,placeacheckintheappropriatebox.Next, total the check marks for each section and insert the number in the

designated block.Nowdo the arithmetic indicated and insert your percent foreacharea.

*Thesubjectareashavebeenexpandedtoidentifyspecificareasinthetext.

*Thesubjectareashavebeenexpandedtoidentifyspecificareasinthetext.

AnswerSheetPRACTICETEST3

Determine the correct answer for each question. Then, using a No. 2pencil,blackencompletelytheovalcontainingtheletterofyourchoice.

PracticeTest3Note: For all questions involving solutions and/or chemical equations, assumethatthesystemisinwaterunlessotherwisestated.

Reminder:Youmaynotuseacalculatoronthesetests.Thefollowingsymbolshavethemeaningslistedunlessotherwisenoted.

H=enthalpy g=gram(s)M=molar J=joules(s)n=numberofmoles kJ=kilojoulesP=pressure L=liter(s)R=molargasconstant mL=milliliter(s)S=entropy mm=millimeter(s)T=temperature mol=mole(s)V=volume V=volt(s)atm=atmosphere

PartA

Directions: Every set of the given lettered choices below refers to thenumberedstatementsorformulasimmediatelyfollowingit.Choosetheoneletteredchoicethatbestfitseachstatementorformulaandthenfill inthecorresponding oval on the answer sheet. Each choicemay be used once,morethanonce,ornotatallineachset.

Questions1–4refertothefollowingdiagram:

1.Theactivationenergyoftheforwardreactionisshownby

2.Theactivationenergyofthereversereactionisshownby

3.Theheatofthereactionfortheforwardreactionisshownby

4.Thepotentialenergyofthereactantsisshownby

Questions5–7refertothefollowingdiagram:

5.Toplatesilveronthespoon,thepositiontowhichthewirefromthespoonmustbeconnected

6.Thepositionoftheanode

7.Thepositionfromwhichsilverthatisplatedoutemerges

Questions8–11matchthefollowingequationstotheappropriatedescriptions:

8.Thisequationshowsthevolumedecreasingasthepressureisincreasedwhenthetemperatureisheldconstant.ItisanexampleofBoyle’sLaw.

9.Thisequationshowsthepressureincreasingasthetemperatureisincreasedwhenthevolumeisheldconstant.ItisanexampleofGay-Lussac’sLaw.

10.Thisequationshowsthevolumeincreasingasthetemperatureisincreasedwhenthepressureisheldconstant.ItisanexampleofCharles’sLaw.

11.Thisequationshowsthatthetotalpressureofamixtureofgasesisequaltothesumofthepartialpressuresofthecomponentgases.

Questions12–14

(A)1(B)2(C)3(D)4(E)5

12.Whenthefollowingequation:Cu(s)+HNO3(aq)→Cu(NO3)2(aq)+H2O()+NO(g)isbalanced,whatwillbethecoefficient,inthelowestwholenumber,ofCu?

13.If6molesofCureactedaccordingtotheabovebalancedequation,whatwillbethenumberofmolesofNOthatwouldbeformed?

14.IfCu(NO3)2goesintosolutionasions,whatwillbethenumberofionsintowhichitwilldissociate?

Questions15–18

(A)Ionicsubstance(B)Polarcovalentsubstance(C)Nonpolarcovalentsubstance(D)Amorphoussubstance(E)Metallicnetwork

15.MgCl2(s)

16.HCl(g)

17.CH3–CH3(g)

18.Cu(s)

Questions19–23

(A)Brownianmovement(B)Litmuspaperreaction(C)Phenolphthaleinreaction(D)Dehydration(E)Deliquescent

19.ThereasonwhyabluecrystalofCuSO4·5H2Oturnswhitewhenheated

20.Thezigzagpathofcolloidalparticlesinlight

21.Thepinkcolorinabasicsolution

22.Thepinkcolorinanacidsolution

23.Theadsorbtionofwatertothesurfaceofacrystal

PartB

ONTHEACTUALCHEMISTRYTEST,THEFOLLOWINGTYPEOFQUESTION MUST BE ANSWERED ON A SPECIAL SECTION(LABELED“CHEMISTRY”)ATTHELOWERLEFT-HANDCORNEROF YOUR ANSWER SHEET. THESE QUESTIONS WILL BENUMBERED BEGINNING WITH 101 AND MUST BE ANSWEREDACCORDINGTOTHEFOLLOWINGDIRECTIONS.

Directions: Every question below contains two statements, I in the left-handcolumnandIIintheright-handcolumn.Foreachquestion,decideifstatementIistrueorfalseandifstatementIIistrueorfalseandfillinthecorrespondingTorFovalsonyouranswersheet.*FillinovalCEonlyifstatementIIisacorrectexplanationofstatementI.

SampleAnswerGrid:

CHEMISTRY*FillinovalCEonlyifIIisacorrectexplanationofI.

I II101.Elementsintheupper/left

cornerofthePeriodicTableareactivemetals

BECAUSEmetalshavelargerionicradiithantheiratomicradii.

102.Asynthesisreactionthatisnonspontaneousandhasanegativevalueforitsheatofreactionwillnotoccuruntilsomeheatisadded

BECAUSEnonspontaneousexothermicreactionsneedenoughactivationenergytogetthemstarted.

103.Transitionelementsinaparticularperiodmayhavethesameoxidationnumber

BECAUSEtheyhaveacompleteouterenergylevel.

104.Whenacrystalisaddedtoasupersaturatedsolutionofitself,thecrystaldoesnotappeartochange

BECAUSEthesupersaturatedsolutionisholdingmoresolutethanitsnormalsolubility.

105.Equilibriumisastaticcondition

BECAUSEatequilibrium,theforwardreactionrateequalsthereversereactionrate.

106.Theionicbondisthestrongestbond

BECAUSEionicbondshaveelectrostaticattractionduetothelossandgainofelectron(s).

107.IntheequilibriumreactionN2(g)+3H2(g)↔2NH3(g)+heatwhenthepressureinthereactionchamberisincreased,thereactionshiftstotheright

BECAUSE

theincreaseinpressurecausesthereactiontoshifttotherighttodecreasethepressuresince4volumesontheleftbecome2volumesontheright.

108.Iftheforwardreactionofanequilibriumisexothermic,addingheattothesystemfavorsthereversereaction

BECAUSE

additionalheatcausesastressonthesystem,andthesystemmovesinthedirectionthatreleasesthestress.

109.Anelementthathasanelectronconfigurationof1s2

2s22p63s23p63d34s2isatransitionelement

BECAUSEthetransitionelementsfromscandiumtozincarefillingthe3dorbitals.

110.Themostelectronegativeelementsintheperiodicchartarefoundamongnonmetals

BECAUSEelectronegativityisameasureoftheabilityofanatomtodrawvalenceelectronstoitself.

111.Basicanhydridesreactinwatertoformbases

BECAUSE

metallicoxidesreactwithwatertoformsolutionsthathaveanexcessofhydroxideions.

112.Thereare3molesofatomsin18gramsofwater

BECAUSE thereare6×1023atomsin1mole.

113.Benzeneisagoodelectrolyte BECAUSEagoodelectrolytehaschargedionsthatcarrytheelectriccurrent.

114.Normalbutylalcoholand2-butanolareisomers

BECAUSEisomersvaryinthenumberofneutronsinthenucleusoftheatom.

115.ThereactionofCaCO3andHClgoestocompletion

BECAUSEreactionsthatformaprecipitatetendtogotocompletion.

116.AlargenumberofalphaparticlesweredeflectedintheRutherfordexperiment

BECAUSEalphaparticlesthatcameclosetothenucleusofthegoldatomsweredeflected.

PartC

Directions:Everyquestionor incompletestatementbelowis followedbyfivesuggestedanswersorcompletions.Choosetheonethatisbestineachcaseandthenfillinthecorrespondingovalontheanswersheet.

24.Whatarethesimplestwhole-numbercoefficientsthatbalancethis

equation?

...C4H10+...O2→...CO2+...H2O

(A)1,6,4,2(B)2,13,8,10(C)1,6,1,5(D)3,10,16,20(E)4,26,16,20

25.HowmanyatomsarepresentintheformulaKAl(SO4)2?

(A)7(B)9(C)11(D)12(E)13

26.AllofthefollowingarecompoundsEXCEPT

(A)coppersulfate(B)carbondioxide(C)washingsoda(D)air(E)lime

27.Whatvolumeofgas,inliters,would2molesofhydrogenoccupyatSTP?

(A)11.2(B)22.4(C)33.6(D)44.8(E)67.2

28.Whatisthemaximumnumberofelectronsheldinthedorbitals?

(A)2(B)6(C)8(D)10

(E)14

29.Ifanelementhasanatomicnumberof11,itwillcombinemostreadilywithanelementthathasanelectronconfigurationof

(A)1s22s22p63s23p1

(B)1s22s22p63s23p2

(C)1s22s22p63s23p3

(D)1s22s22p63s23p4

(E)1s22s22p63s23p5

30.Anexampleofaphysicalpropertyis

(A)rusting(B)decay(C)souring(D)lowmeltingpoint(E)highheatofformation

31.AgasatSTPthatcontains6.02×1023atomsandformsdiatomicmoleculeswilloccupy

(A)11.2L(B)22.4L(C)33.6L(D)67.2L(E)1.06qt

32.Whenexcitedelectronscascadetolowerenergylevelsinanatom,

(A)visiblelightisalwaysemitted(B)thepotentialenergyoftheatomincreases(C)theelectronsalwaysfallbacktothefirstenergylevel(D)theelectronsfallindiscriminatelytoalllevels(E)theelectronsfallbacktoalowerunfilledenergylevel

33.Massspectroscopyusestheconceptthat

(A)chargedparticlesareevenlydeflectedinamagneticfield(B)chargedparticlesaredeflectedinamagneticfieldinverselytothemass

oftheparticles(C)particlesofheaviermassaredeflectedinamagneticfieldtoagreater

degreethanlighterparticles(D)particlesareevenlydeflectedinamagneticfield

34.Thebondthatincludesanupperandalowersharingofelectronorbitalsiscalled

(A)apibond(B)asigmabond(C)ahydrogenbond(D)acovalentbond(E)anionicbond

35.WhatistheboilingpointofwateratthetopofPikesPeak?

(A)Itis100°C.(B)Itis>100°Csincethepressureislessthanatgroundlevel.(C)Itis<100°Csincethepressureislessthanatgroundlevel.(D)Itis>100°Csincethepressureisgreaterthanatgroundlevel.(E)Itis<100°Csincethepressureisgreaterthanatgroundlevel.

36.Theatomicstructureofthealkaneseriescontainsthehybridorbitalsdesignatedas

(A)sp(B)sp2

(C)sp3

(D)sp3d2

(E)sp4d3

37.Whichofthefollowingis(are)trueforthisreaction?

Cu+4HNO3→Cu(NO3)2+2H2O+2NO2(g)

I.Itisanoxidation-reductionreaction.II.Copperisoxidized.III.Theoxidationnumberofnitrogengoesfrom+5to+4.

(A)Ionly

(B)IIIonly(C)IandIIonly(D)IIandIIIonly(E)I,II,andIII

38.Whichofthefollowingpropertiescanbeattributedtowater?

I.Ithasapermanentdipolemomentattributedtoitsmolecularstructure.II.Itisaverygoodconductorofelectricity.III.Ithasitspolarcovalentbondswithhydrogenonoppositesidesofthe

oxygenatom,sothatthemoleculeislinear.

(A)Ionly(B)IIIonly(C)IandIIonly(D)IIandIIIonly(E)I,II,andIII

39.AllofthefollowingstatementsaretrueforthisreactionEXCEPT

HCl(g)+H2O(l)→H3O+(aq)+Cl–(aq)

(A)H3O+istheconjugateacidofH2O.

(B)Cl–istheconjugatebaseofHCl.(C)H2OisbehavingasaBrønsted-Lowrybase.(D)HClisaweakerBrønsted-LowryacidthanH2O.(E)Thereactionessentiallygoestocompletion.

40.Anuclearreactormustincludewhichofthefollowingparts?

I.ElectricgeneratorII.FissionablefuelelementsIII.Moderator

(A)Ionly(B)IIIonly(C)IandIIonly(D)IIandIIIonly(E)I,II,andIII

41.Whichofthefollowingsaltswillhydrolyzeinwatertoformbasicsolutions?

I.NaClII.CuSO4

III.K3PO4

(A)Ionly(B)IIIonly(C)IandIIonly(D)IIandIIIonly(E)I,II,andIII

42.When1moleofNaClisdissolvedin1,000gramsofwater,theboilingpointofthewaterischangedto

(A)100.51°C(B)101.02°C(C)101.53°C(D)101.86°C(E)103.62°C

43.WhatisthestructureassociatedwiththeBF3molecule?

(A)Linear(B)Trigonalplanar(C)Tetrahedron(D)Trigonalpyramidal(E)BentorV-shaped

Questions44and45refertothefollowingsetup:

44.Whatletterdesignatesanerrorinthislaboratorysetup?

(A)A(upperpartoftube)(B)B(lowerpartoftube)(C)C(D)D(E)E

45.Ifthereactioninquestion44createdagas,wherewouldthecontentsoftheflaskbeexpelledundertheseconditions?

(A)A(B)B(C)C(D)D(E)E

46.Themostactivenonmetalhas

(A)ahighelectronegativity(B)alowelectronegativity(C)amediumelectronegativity(D)largeatomicradii(E)adeliquescentproperty

47.InthereactionFe+S→FeS,whichistrue?

(A)Fe+2e–→Fe2+

(B)Fe→Fe2++2e–

(C)Fe2+→Fe+2e–

(D)S→S2–+2e–

(E)S2–+2e–→S

48.WhatisthepHofasolutionwithahydroxideionconcentrationof0.00001mole/liter?

(A)–5(B)–1(C)5(D)9(E)14

49.Electrolysisofadilutesolutionofsodiumchlorideresultsinthecathodeproduct

(A)sodium(B)hydrogen(C)chlorine(D)oxygen(E)peroxide

50......C2H4(g)+.....O2(g)→.....CO2(g)+.....H2O(l)Iftheequationfortheabovereactionisbalancedwithwhole-numbercoefficients,whatisthecoefficientforoxygengas?

(A)1(B)2(C)3(D)4(E)5

51.5.00litersofgasatSTPhaveamassof12.5grams.Whatisthemolarmassofthegas?

(A)12.5g/mol(B)25.0g/mol(C)47.5g/mol(D)56.0g/mol(E)125g/mol

52.Acompoundwhosemolecularmassis90.0gramscontains40.0%carbon,6.67%hydrogen,and53.33%oxygen.Whatisthetrueformulaofthecompound?

(A)C2H2O4

(B)CH2O4

(C)C3H6O(D)C3HO3

(E)C3H6O3

53.HowmanymolesofCaOareneededtoreactwithanexcessofwatertoform370gramsofcalciumhydroxide?

(A)1.0(B)2.0(C)3.0(D)4.0(E)5.0

54.Towhatvolume,inmilliliters,must50.0millilitersof3.50MH2SO4bedilutedinordertomake2.00MH2SO4?

(A)25.0(B)60.1(C)87.5(D)93.2(E)101

55.AsmallvalueofKeqindicatesthatequilibriumoccurs

(A)atalowproductconcentration(B)atahighproductconcentration(C)afterconsiderabletime(D)withthehelpofacatalyst(E)withnoforwardreaction

56.Astudentmeasured10.0millilitersofanHClsolutionintoabeakerandtitrateditwithastandardNaOHsolutionthatwas0.09M.Theinitial

NaOHburettereadingwas34.7milliliterswhilethefinalreadingshowed49.2milliliters.

WhatisthemolarityoftheHClsolution?

(A)0.13(B)0.47(C)0.52(D)1.57(E)2.43

57.Astudentmadethefollowingobservationsinthelaboratory:

(a)Sodiummetalreactedvigorouslywithwaterwhileastripofmagnesiumdidnotseemtoreactatall.

(b)Themagnesiumstripreactedwithdilutehydrochloricacidfasterthananironstrip.

(c)Acopperrivetsuspendedinsilvernitratesolutionwascoveredwithsilver-coloredstalactitesinseveraldays,andtheresultingsolutionhadabluecolor.

(d)Ironfilingsdroppedintothebluesolutionwerecoatedwithanorangecolor.

Theorderofdecreasingstrengthasreducingagentsis:

(A)Na,Mg,Fe,Ag,Cu(B)Mg,Na,Fe,Cu,Ag(C)Ag,Cu,Fe,Mg,Na(D)Na,Fe,Mg,Cu,Ag(E)Na,Mg,Fe,Cu,Ag

58.Astudentplacedwater,sodiumchloride,potassiumdichromate,sand,chalk,andhydrogensulfideintoadistillingflaskandproceededtodistill.Whatingredientbesideswaterwouldbefoundinthedistillate?

(A)Sodiumchloride(B)Chalk(C)Sand(D)Hydrogensulfide(E)Chromesulfate

59.WhichofthesestatementsisNOTcorrect?

(A)Inanexothermicreaction,ΔHisnegativeandtheenthalpydecreases.(B)Inanendothermicreaction,ΔHispositiveandtheenthalpyincreases.(C)InareactionwhereΔGisnegative,theforwardreactionisspontaneous.(D)InareactionwhereΔGispositive,ΔSmayalsobepositive.(E)InareactionwhereΔHispositiveandΔSisnegative,theforward

reactionisspontaneous.

60.Astudentfilledasteam-jacketedeudiometerwith32.millilitersofoxygenand4.0millilitersofhydrogenovermercury.Howmuchofwhichgaswouldbeleftuncombinedafterthemixturewassparked?

(A)Noneofeither(B)3.0mLH2

(C)24mLO2

(D)28mLO2

(E)30.mLO2

61.Whatwouldbethetotalvolume,inmilliliters,ofgasesinquestion60aftersparking?

(A)16(B)24(C)34(D)36(E)40

62.Howcantheadditionofacatalystaffectanexothermicreaction?

I.Speedupthereaction.II.Slowdownthereaction.III.Increasetheamountofproductformed.

(A)Ionly(B)IIonly(C)IandIIonly(D)IIandIIIonly(E)I,II,andIII

63.Inwhichperiodoftheperiodictableisthemostelectronegativeelementfound?

(A)1(B)2(C)3(D)4(E)5

64.Whatcouldbetheequilibriumconstantforthisreaction:aA+bB cC+dD,ifAandDaresolids?

(A)

(B)

(C)

(D)

(E)[A]a[B]b[C]c[D]d

65.WhichofthefollowingdoesNOTreactwithadilutesolutionofsulfuricacid?

(A)NaNO3

(B)Na2S(C)Na3PO4

(D)Na2CO3

(E)NaOH

66.Whichofthesestatementsisthebestexplanationforthesp3hybridizationofcarbon’selectronsinmethane,CH4?

(A)Theneworbitalsareonesorbitalandthreeporbitals.(B)Theselectronispromotedtotheporbitals.(C)Thesorbitalisdeformedintoaporbital.

(D)Fournewandequivalentorbitalsareformed.(E)Thesorbitalelectronlosesenergytofallbackintoapartiallyfilledp

orbital.

67.Theintermolecularforcethatismostsignificantinexplainingthevariationoftheboilingpointofwaterfromtheboilingpointsofsimilarlystructuredmoleculesis

(A)hydrogenbonding(B)vanderWaalsforces(C)covalentbonding(D)ionicbonding(E)coordinatecovalentbonding

68.IfKforthereactionH2+I2 2HIisequalto45.9at450°C,and1moleofH2and1moleofI2areintroducedintoa1-literboxatthattemperature,whatwillbetheexpressionforKatequilibrium?

(A)

(B)

(C)

(D)

(E)

69.Whatisthemolarmassofanonionizingsolidif10.gramsofthissolid,dissolvedin200.gramsofwater,formedasolutionthatfrozeat–3.72°C?

(A)25.g/mol(B)50.g/mol(C)100.g/mol(D)150.g/mol(E)1,000.g/mol

Ifyoufinishbeforeonehourisup,youmaygobacktocheckyourworkorcompleteunansweredquestions.

AnswerKeyP R A C T I C E T E S T 3

1.B 13.D 101.T,F2.D 14.C 102.T,T,CE3.C 15.A 103.T,F4.A 16.B 104.F,T5.B 17.C 105.F,T6.D 18.E 106.T,T,CE7.E 19.D 107.T,T,CE8.C 20.A 108.T,T,CE9.B 21.C 109.T,T,CE10.A 22.B 110.T,T,CE11.D 23.E 111.T,T,CE12.C 112.T,T

113.F,T114.T,F115.T,T116.F,T

24.B 40.D 56.A25.D 41.B 57.E26.D 42.B 58.D

27.D 43.B 59.E28.D 44.C 60.E29.E 45.A 61.C30.D 46.A 62.A31.A 47.B 63.B32.E 48.D 64.C33.B 49.B 65.A34.A 50.C 66.D35.C 51.D 67.A36.C 52.E 68.B37.E 53.E 69.A38.A 54.C39.D 55.A

ANSWERSEXPLAINED1.(B)Theactivationenergyoftheforwardreactionistheenergyneededtobeginthereaction.

2.(D)Forthereversereactiontooccur,activationenergyequaltothesumof(B)+(C)isneeded.Thisisshownby(D).

3. (C) The heat of the reaction is the heat liberated between the level ofpotentialenergyofthereactantsandthatoftheproducts.Thisisquantity(C)onthediagram.

4. (A) The potential energy of the reactants is the total of the originalpotentialenergiesofthereactantsshownby(A).

5.(B)ThespoonmustbemadethecathodetoattracttheAg+ions.

6.(D)Thesilverplateistheanode.

7.(E)ThesolutionofAg+providesthesilverforplating.

8. (C) This equation shows the volume decreasing as the pressure isincreased when the temperature is held constant. It is an example ofBoyle’sLaw.

9. (B) This equation shows the pressure increasing as the temperature isincreasedwhen the volume is held constant. It is an example of Gay-Lussac’sLaw.

10. (A) This equation shows the volume increasing as the temperature isincreased when the pressure is held constant. It is an example ofCharles’sLaw.

11.(D)Thisequationshowsthat thetotalpressureofamixtureofgasesisequaltothesumofthepartialpressuresofthecomponentgases.

12–14.Thebalancedequationswithhalf-reactionsareasfollows:

12.(C)

13.(D)Thecoefficientsshowthat3molofCuproduces2molofNO,so6molofCuproduces4molofNO.

14. (C) The expression Cu(NO3)2 → Cu2+ + 2NO3– shows that the

dissociationyields3ions.

15. (A)MgCl2 is ionic because it is the product of an activemetal (Mg)combiningwithaveryactivenonmetal(Cl).

16. (B)Theelectronegativitydifferencebe tweenHandCl isbetween0.5and1.7.Thisindicatesanunequalsharingofelectrons,whichresultsinapolarcovalentbond.

17.(C)Ethane,CH3–CH3(g),hassymmetricallyarrangedC–Hpolarbondssothattheethanemoleculeisnonpolarcovalent.

18.(E)Cu(s)isametal.

19.(D)Whenhydratedcoppersulfateisheated,thecrystalcrumplesasthewaterisforcedoutofthestructure,andawhitepowderistheresult.

20. (A) Brownianmovement is due tomolecular collisions with colloidalparticles,whichknocktheparticlesaboutinazigzagpathnotedbythereflectedlightfromtheseparticles.

21.(C)Theindicatorphenolphthaleinturnspinkinabasicsolution.

22.(B)Litmuspaperturnspinkinanacidsolution.

23.(E)Asubstancethatisdeliquescent,suchasacrystal,drawswatertoitssurface.Attimesitcandrawenoughwatertoformawatersolution.

101.(T,F)Theassertionistruethatthemostactivemetalsarefoundintheupper left corner of the Periodic Table because of their ability to losetheir outer electron(s). These metals actually have smaller ionic radiithantheiratomicradii.

102.(T,T,CE)Theassertionisexplainedbythereason.Thegraphicdisplayofthisis:

103.(T,F)Theassertionistruebutthereasoningisfalse.Transitionelementshave incomplete inner energy levels that are being filled with theadditionalelectrons,thusleavingtheouterenergylevelthesameinmostcases.Asaresult,theseelementshavecommonoxidationnumbers.

104. (F, T) The assertion is false and the reason is true. A supersaturatedsolutionisholdingmorethanitsnormalsolubility,andtheadditionofacrystalcausescrystallizationtooccur.

105.(F,T)Equilibriumisadynamicconditionbecauseofthereasonstated.Theassertionisfalse;thereason,true.

106.(T,T,CE)Bothstatementsaretrue,andthereasonexplainswhyionicbondingisthestrongest.

107. (T, T, CE) An equilibrium system must have a gaseous reactant orproduct for pressure to affect the equilibrium.Then increased pressurewill cause the reaction to go in the direction that reduces theconcentrationofgaseoussubstances.Sincefourvolumesofgasesontheleftbecametwovolumesontheright,thereactionshiftstotheright.

108.(T,T,CE)Theassertionisexplainedbythereason;botharetrue.

109.(T,T,CE)Boththeassertionandthereasonaretrue; theyexplainthattheelement’sorbitaldesignationplacesitinthefirsttransitionseriesoffillingthe3dorbitals.

110. (T, T,CE) The assertion is true; the reason is true and explains whynonmetalshavethehighestelectronegativity.

111.(T,T,CE)Theassertionisexplainedbythereason;botharetrue.

112.(T,T)Thereare3molesofatomsin18gofwaterbecause18gis1molofwatermoleculesandeachmoleculehasthreeatoms.Thereasondoesnotexplaintheassertionbutisalsotrue.

113.(F,T)Benzeneisanonionizingsubstanceandthereforeanonelectrolyte.Thereasonisatruestatement.

114. (T, F) Isomers have the same empirical formula but vary in theirstructuralformulas.

115. (T, T) The reaction does go to completion, but a gaseous product isformed,notaprecipitate,soIIdoesnotexplainI.

116. (F,T) In theRutherfordexperiment relativelyfewalphaparticlesweredeflected,indicatingagreatdealofemptyspaceintheatom.Thereasonisatruestatement.

24.(B)Thecorrectcoefficientsare2,13,8,and10.

25.(D)1K+1Al+2S+8O=12total

26. (D) Air is a mixture; all others are compounds.Washing soda (C) issodiumcarbonate,andlime(E)iscalciumoxide.

27.(C)OnemoleofagasatSTPoccupies22.4L.SotwomolesofagasatSTPoccupy2.0mol×22.4L=44.8L.

28.(D)Themaximumnumberofelectronsineachkindoforbitalis:

s=2inoneorbitalp=6inthreeorbitalsd=10infiveorbitalsf=14insevenorbitals

29.(E)Theelementwithatomicnumber11issodiumwith1electroninthe3sorbital.Itwouldreadilycombinewiththeelementthathas3p5astheouterorbitalsinceitneedsonly1moreelectrontofillit.

30.(D)Theonlyphysicalpropertynamedinthelistislowmeltingpoint.

31.(A)Ifthegasisdiatomic,then6.02×1023atomswillform6.02×1023/2molecules.At STP, 6.02 × 1023molecules occupy 22.4L, so half thatnumberwilloccupy11.2L.

32.(E)Cascadingexcitedelectronscanfallonlytolowerenergylevelsthatareunfilled.

33. (B) Mass spectroscopy uses a magnetic field to separate isotopes bybending their path. The lighter ones are bent farther than the heavierones.

34.(A)Thepibondisabondbetweentwoporbitals,likethis:

35. (C)AtPikesPeak(alt.approx.14,000ft) thepressure is lower thanatground level; therefore the vapor pressure at a lower temperature willequaltheoutsidepressureandboilingwilloccur.

36.(C)Thealkanescontainthesp3hybridorbitals.

37.(E)I,II,andIIIarecorrect.

38.(A)OnlyIiscorrect.

39.(D)HClisactuallyastrongerBrønsted-LowryacidthanH2O,whichiswhythereactionoccursasshown.

40.(D)Iisnotnecessaryforthereactor,butoftennuclearenergyisusedtooper ate an electric generator. The others, II and III, are necessary forfuelandneutron-speedcontrol,respectively.

41.(B)IIIisasaltfromastrongbaseandaweakacid,whichhydrolyzestoformabasicsolutionwithwater.

42. (B) Since the boiling point is increased by 0.51°C for each mole ofparticles,1molofNaCl→Na++Cl–gives2molofparticles.Thereforetheboilingpointwillbe1.02°higheror101.02°C.

43.(B)TheVSEPRmodelshowsBF3istrigonalplanarandsoisrelatedtothetriangleshapeononeplane.

44.(C)Thedeliverytubeisbelowthefluidlevelintheflaskandwillcauseliquidtobeforcedupthethistletubewhengasisevolvedinthereaction.

45. (A) At first the fluid will be expelled up the thistle tube by the gasgeneratedandexertingpressureinthereactionflask.Whenthelevelofthe fluid falls below the end of the thistle tube, the gas will then bereleasedthroughthethistletube.

46.(A)Themostactivenonmetalhasahighattractionforanotherelectron—thushighelectronegativity.

47.(B)FeloseselectronstoformtheFE2+ion.

48.(D)TheKwofwater=[H+][OH–]=10–14.If[OH–]=10–5mol/L,then

[H+]=10–14/10–5=10–9

pH=–log[H+](bydefinition)pH=–[–9]pH=9

49.(B)WhendiluteNaClsolutioniselectrolyzed,hydrogenisgivenoffatthecathode,chlorineisgivenoffattheanode,andsodiumhydroxideisleftinthecontainer.

50.(C)Thecorrectlybalancedequationis

C2H4(g)+3O2(g)→2CO2(g)+2H2O(l)

51.(D)OnemoleofagasatSTPoccupies22.4L.

52. (E) To find the simple or empirical formula, divide each % by theelement’satomicmass.

Carbon40÷12=3.333

Hydrogen6.67÷1=6.67

Oxygen53.33÷16=3.33

Next,divideeachquotientbythesmallestquotient inanattempt togetsmallwholenumbers.

3.33÷3.33=1C6.67÷3.33=2H3.33÷3.33=1O

ThesimplestformulaisCH2O,whichhasamolecularmassof30.Thetruemolecularmassisgivenas90.0,whichis threetimesthesimplest.ThereforethetrueformulaisC3H6O3.

53.(E)Thereactionis:

xmol370gCao+H2O→Ca(OH)2Ca(OH)2molecularmass=74

370g÷74=5.0molofCa(OH)2iswanted.Thereactionequationshows1molofCaOproduces1molofCa(OH)2,sotheansweris5.0mol.

54.(C)Indilutionproblems,thisformulacanbeused:

Mbefore×Vbefore=Mafter×Vafter

Substitutinggives:

3.50×50.0=2×(?x)

x=87.5mL,newvolumeafterdilution

55. (A) For Keq to be small, the numerator, which is made up of theconcentration(s)of theproduct(s)atequilibrium,mustbesmaller thanthedenominator.

56.(A)TheamountofNaOHusedis49.2–34.7=14.5mLUsingM1×V1=M2×V2gives0.09M×14.5mL=M2×10mLM2=0.13M

57.(E)Thereactionsrecordedindicatedthattheeaseoflosingelectronsisgreater in sodium than magnesium, greater in magnesium than iron,greaterinironthancopper,andfinallygreaterincopperthansilver.

58. (D) Distillation removes only dissolved solids from the distillate. Thevolatilegases,suchasH2S,willbecarriedintothedistillate.

59.(E)Allthefirstfourstatementsarecorrect.

TheGibbsfree-energyequationis:

ΔG=ΔH–TΔS

In choice (E), if ΔH is positive and ΔS is negative, then ΔG willdefinitely be positive, which means that the forward reaction will notoccurspontaneously.

60. (E) H2 to O2 ratio by volume is 2 : 1 in the formation of water.Therefore,4.0mLH2will reactwith2.0mLofO2 tomake4.0mLofsteam.

2H2(g)+O2(g)→2H2O(g)

Thisleaves30.mLofO2uncombined.

61.(C)Therewillbe30.mLofO2+4.0mLofsteam=34mLtotal.

62.(A)Bydefinition,acatalystcanbeusedtospeedupareactionwithoutitselfbeingconsumed,soIiscorrect.

63.(B)Themostelectronegativeelementisfluorine(F),foundinperiod2.

64.(C)SolidsareincorporatedintotheKvalueandthereforedonotappearontherightsideoftheequation.

65.(A)OnlyNaNO3willnotreactbecauseitrequiresheattoreact.

66. (D)When hybridization forms the sp3 orbitals in methane, CH4, fourentirelyneworbitals,differentfrombutequivalenttotheformersandporbitals,result.

67.(A)Hydrogenbondingbetweenwatermoleculescausestheboilingpointtobehigherthanwouldbeexpected.

68.(B)Atthebeginningofthereaction

[H2]=1mol/L[I2]=1mol/L[HI]=0

Atequilibrium

(H2+I2 2HI)(Letx=moles/literofH2andI2inHIform)

[H2]=(1–x)mol/L[I2]=(1–x)mol/L[HI]=2xmol/L

Then,substitutingtheabovevaluesintotheequation,youget:

69.(A)10.g/200.gofwater=50.g/1,000.gofwater(5timesasmuch)

The freezingpoint depression, 3.72°, is dividedby1.86°,which is thedepressioncausedby1molin1,000.gofwater,tofindhowmanymolesaredissolved.

3.72°÷1.86°=2mol

If50.gcausedthisdepressionandisequalto2mol,then1molwouldbe of50.g,or25g.So,themolarmassofthesolidis25g/mol.

CALCULATINGYOURSCOREYour scoreonPracticeTest3 cannowbe computedmanually.Theactual testwill be scored bymachine, but the samemethod is used to arrive at the rawscore.Yougetonepoint foreachcorrectanswer.Foreachwronganswer,youloseone-fourthofapoint.Questions thatyouomitor thathavemorethanoneanswerarenotcounted.Onyouranswersheetmarkallcorrectanswerswitha“C”andallincorrectanswerswithan“X”.

DeterminingYourRawTestScoreTotalthenumberofcorrectanswersyouhaverecordedonyouranswersheet.ItshouldbethesameasthetotalofallthenumbersyouplaceintheblockinthelowerleftcornerofeachareaoftheSubjectAreasummaryinthenextsection.

A.Enterthetotalnumberofcorrectanswershere:________Nowcountthenumberofwronganswersyourecordedonyouranswersheet.

B.Enterthetotalnumberofwronganswershere:________MultiplythenumberofwronganswersinBby0.25.

C.Enterthatproducthere:________SubtracttheresultinCfromthetotalnumberofrightanswersinA.

D.Entertheresultofyoursubtractionhere:________

E.RoundtheresultinDtothenearestwholenumber:________.Thisisyourrawtestscore.

ConversionofRawScorestoScaledScoresYour raw score is converted by the College Board into a scaled score. TheCollegeBoardscoresrangefrom200to800.ThisconversionisdonetoensurethatascoreearnedonanyeditionofaparticularSATSubjectTestinChemistryiscomparabletothesamescaledscoreearnedonanyothereditionofthesametest.Becausesomeeditionsofthetestsmaybeslightlyeasierormoredifficultthan others, scaled scores are adjusted so that they indicate the same level ofperformance regardless of the edition of the test taken and the ability of the

group that takes it. Consequently, a specific raw score on one edition of aparticulartestwillnotnecessarilytranslatetothesamescaledscoreonanothereditionofthesametest.Becausethepracticetestsinthisbookhavenolargepopulationofscoreswith

whichtheycanbescaled,scaledscorescannotbedetermined.Results from previous SAT Chemistry tests appear to indicate that the

conversionofrawscorestoscaledscoresGENERALLYfollowsthispattern:

Note that this scale provides only a general idea of what a raw score maytranslateintoonascaledscorerangeof800–200.Scalingoneverytestisusuallyslightly different. Some students who had taken the SAT Subject Test inChemistry after using this book had reported that they have scored slightlyhigherontheSATtestthanonthepracticetestsinthisbook.Theyallreportedthatpreparingwellforthetestpaidoffinabetterscore!

DIAGNOSINGYOURNEEDSAftertakingPracticeTest3,checkyouranswersagainstthecorrectones.Thenfillinthechartbelow.Inthespaceundereachquestionnumber,placeacheckifyouansweredthat

questioncorrectly.

EXAMPLE:

Ifyouranswertoquestion5wascorrect,placeacheckintheappropriatebox.Next, total the check marks for each section and insert the number in the

designated block.Nowdo the arithmetic indicated and insert your percent foreacharea.

*Thesubjectareashavebeenexpandedtoidentifyspecificareasinthetext.

*Thesubjectareashavebeenexpandedtoidentifyspecificareasinthetext.

AnswerSheetPRACTICETEST4

Determine the correct answer for each question. Then, using a No. 2pencil,blackencompletelytheovalcontainingtheletterofyourchoice.

PracticeTest4Note:For all questions involving solutions and/or chemical equations, assumethatthesystemisinwaterunlessotherwisestated.

Reminder:Youmaynotuseacalculatoronthesetests.Thefollowingsymbolshavethemeaningslistedunlessotherwisenoted.

H=enthalpy T=temperature L=liter(s)M=molar V=volume mL=milliliter(s)n=numberofmoles atm=atmosphere mm=millimeter(s)

P=pressure g=gram(s) mol=mole(s)R=molargasconstant J=joules(s) V=volt(s)

S=entropy kJ=kilojoules

PartA

Directions: Every set of the given lettered choices below refers to thenumberedstatementsorformulasimmediatelyfollowingit.Choosetheoneletteredchoicethatbestfitseachstatementorformulaandthenfill inthecorresponding oval on the answer sheet. Each choicemay be used once,morethanonce,ornotatallineachset.

Questions1–3refertothefollowinggraphs:

1.Thegraphthatbestshowstherelationshipofgasvolumetotemperature,

withpressureheldconstant

2.Thegraphthatbestshowstherelationshipofgasvolumetopressure,withtemperatureheldconstant

3.Thegraphthatbestshowstherelationshipofthenumberofgramsofasolidthataresolublein100gramsofH2Oatvaryingtemperaturesifthesolubilitybeginsatasmallquantityandincreasesataslow,steadypaceasthetemperatureisincreased

Questions4–7

(A)Amolecule(B)Amixtureofcompounds(C)Anisotope(D)Anisomer(E)Anacidsalt

4.Thesimplestunitofwaterthatretainsitsproperties

5.Acommercialcakemix

6.Anatomwiththesamenumberofprotonsasanotheratomofthesameelementbutadifferentnumberofneutrons

7.ClassificationofCa(HCO3)2

Questions8–10

(A)1(B)6(C)9(D)10(E)14

8.Theatomicnumberofanatomwithanelectrondotarrangementsimiliarto

9.ThenumberofatomsrepresentedintheformulaNa2CO3

10.ThenumberthatrepresentsthemostacidpH

Questions11–14

(A)Density(B)Equilibriumconstant(C)Molarmass(D)Freezingpoint(E)Molarity

11.Canbeexpressedinmolesofsoluteperliterofsolution

12.Canbeexpressedingramsperliterofagas

13.WillNOTbeaffectedbychangesintemperatureandpressure

14.AtSTP,canbeusedtodeterminethemolecularmassofapuregas

Questions15–18

(A)Buffer(B)Indicator(C)Arrheniusacid(D)Arrheniusbase(E)Neutralcondition

15.ResistsarapidchangeofpH

16.Exhibitsdifferentcolorsinacidicandbasicsolutions

17.At25°C,theaqueoussolutionhasapH<7.

18.At25°C,theaqueoussolutionhasapH>7.

Questions19–23

(A)H2

(B)SO2

(C)CO(D)HCl(E)O3

19.Inthestratosphere,screensoutalargefractionoftheultravioletraysofthesun.

20.Isaproductoftheincompletecombustionofhydrocarbons.

21.Agasproducedbytheheatingofpotassiumchlorate

22.Agasthatisslightlysolubleinwaterandgivesaweaklyacidsolution

23.Contributestoacidrain.

PartB

ONTHEACTUALCHEMISTRYTEST,THEFOLLOWINGTYPEOFQUESTION MUST BE ANSWERED ON A SPECIAL SECTION(LABELED“CHEMISTRY”)ATTHELOWERLEFT-HANDCORNEROF YOUR ANSWER SHEET. THESE QUESTIONS WILL BENUMBERED BEGINNING WITH 101 AND MUST BE ANSWEREDACCORDINGTOTHEFOLLOWINGDIRECTIONS.

Directions:Every question below contains two statements, I in the left-handcolumnandIIintheright-handcolumn.Foreachquestion,decideifstatementIistrueorfalseandifstatementIIistrueorfalseandfillinthecorrespondingTorFovalsonyouranswersheet.*FillinovalCEonlyifstatementIIisacorrectexplanationofstatementI.

SampleAnswerGrid:

CHEMISTRY*FillinovalCEonlyifIIisacorrectexplanationofI.

I II

101.

AccordingtotheKineticMolecularTheory,theparticlesofagasareinrandommotionaboveabsolutezero

BECAUSE thedegreeofrandommotionofgasmoleculesvariesinverselywiththetemperatureofthegas.

102. Anelectronhaswavepropertiesaswellasparticleproperties

BECAUSE thedesignofaparticularexperimentdetermineswhichpropertiesareverified.

103. Thealkanesareconsideredahomologousseries

BECAUSE

homologousserieshavethesamefunctionalgroupbutdifferinformulabytheadditionofafixedgroupofatoms.

104.Whenanatomofanactivemetalbecomesanion,theradiusoftheionislessthanthatoftheatom

BECAUSE thenucleusofanactivemetallicionhaslesspositivechargethantheelectron“cloud.”

105.Whentheheatofformationforacompoundisnegative,ΔHisnegative

BECAUSE

anegativeheatofformationindicatesthatareactionisexothermicwithanegativeenthalpychange.

106. Waterisapolarsubstance BECAUSE thesharingofthebondingelectronsinwaterisunequal.

107. Acatalystacceleratesachemicalreaction

BECAUSE acatalystlowerstheactivationenergyofthereaction.

108.Copperisanoxidizingagentinthereactionwithsilvernitratesolution

BECAUSE copperloseselectronsinareactionwithsilverions.

109.Therateofdiffusion(oreffusion)ofhydrogengascomparedwiththatofheliumgasis1:4

BECAUSE therateofdiffusion(oreffusion)ofgasesvariesinverselyasthesquarerootofthemolecularmass.

110.Agasheatedfrom10°Cto100°Catconstantpressurewillincreaseinvolume

BECAUSE

asCharles’sLawstates,ifthepressureremainsconstant,thevolumevariesdirectlyastheabsolutetemperaturevaries.

111.TheGibbsfree-energyequationcanbeusedtopredictthesolubilityofasolute

BECAUSE thesolubilityofmostsaltsincreasesastemperatureincreases.

112.Thecompleteelectrolysisof45gramsofwaterwillyield40gramsofH2and5gramsofO2

BECAUSE wateriscomposedofhydrogenandoxygeninaratioof8:1bymass.

113.320caloriesor1.34×103joulesofheatwillmelt4gramsoficeat0°C

BECAUSE theheatoffusionofwateris80caloriespergramor3.34×102joulespergram.

114.

When2litersofoxygengasreactwith2litersofhydrogencompletely,thelimitingfactoristhevolumeoftheoxygen

BECAUSE

thecoefficientsinbalancedequationsofgaseousreactionsgivethevolumerelationshipsoftheenvolvedgases.

115. Waterisagoodsolventforionicand/orpolarcovalentsubstances

BECAUSE watershowshydrogenbondingbetweenoxygenatoms.

116.Ammoniagas,NH3,hasasmallerdensitythanargongas,Ar,atSTP

BECAUSE thedensityofagasatSTPisfoundbydividingthemolarmassby22.4liters.

PartC

Directions:Everyquestionor incompletestatementbelowis followedbyfivesuggestedanswersorcompletions.Choosetheonethatisbestineachcaseandthenfillinthecorrespondingovalontheanswersheet.

24.Inthisgraphicrepresentationofachemicalreaction,whicharrowdepictstheactivationenergyoftheforwardreaction?

(A)A(B)B(C)C(D)D(E)E

25.Howmanyliters(STP)ofO2canbeproducedbycompletelydecomposing2.00molesofKClO3?

(A)11.2(B)22.4(C)33.6(D)44.8(E)67.2

26.Whichofthefollowingstatementsistrue?

(A)Acatalystcannotlowertheactivationenergy.(B)Acatalystcanlowertheactivationenergy.(C)Acatalystaffectsonlytheactivationenergyoftheforwardreaction.(D)Acatalystaffectsonlytheactivationenergyofthereversereaction.(E)Acatalystispermanentlychangedaftertheactivationenergyis

reached.

27.Whichofthefollowingisthecorrectstructuralrepresentationofsodium?

(A) Nucleusandelectronconfiguration:

1s22s22p63s23p64s24p3

(B) Nucleusandelectronconfiguration:

1s22s22p63s23p64s23d14p2

(C) Nucleusandelectronconfiguration:

1s22s22p63s1

(D) Nucleusandelectronconfiguration:

1s22s22p63s23p63d34s2

(E) Nucleusandelectronconfiguration:

1s22s22p63s1

28.IfthemolecularmassofNH3is17,whatisthedensityofthiscompoundatSTP?

(A)0.25g/L(B)0.76g/L(C)1.52g/L(D)3.04g/L(E)9.11g/L

29.Whichbond(s)is(are)ionic?

I.H—Cl(g)II.S—Cl(g)III.Cs—F(s)

(A)Ionly(B)IIIonly(C)IandIIonly(D)IIandIIIonly

(E)I,II,andIII

30.Aromatichydrocarbonsarerepresentedbywhichofthefollowing?

(A)Ionly(B)IIIonly(C)IandIIonly(D)IIandIIIonly(E)I,II,andIII

31.AccordingtoplacementinthePeriodicTable,whichstatement(s)regardingthefirstionizationenergiesofcertainelementsshouldbetrue?

I.LihasahighervaluethanNa.II.KhasahighervaluethanCs.III.NahasahighervaluethanAl.

(A)Ionly(B)IIIonly(C)IandIIonly(D)IIandIIIonly

(E)I,II,andIII

32.Correctlyexpressedhalf-reactionsincludewhichofthefollowing?

I.CrO42−+8H++6e−→Cr3++4H2O

II.I−+6OH−→IO3−+3H2O+6e−

III.MnO4−+2H2O+3e−→MnO2+4OH−

(A)Ionly(B)IIIonly(C)IandIIonly(D)IIandIIIonly(E)I,II,andIII

Questions 33–35. What is the apparent oxidation state (number) of theunderlinedelementinthecompound

33.KHCO3?

(A)+1(B)+2(C)+3(D)+4(E)+5

34.MgSO4?

(A)+1(B)−1(C)+2(D)−2(E)+3

35.CO2?

(A)+2(B)−2(C)+4(D)−4

(E)+5

36.Anatomwithanelectronconfigurationof1s22s22p63s23p4willprobablyexhibitwhichoxidationstate?

(A)+2(B)−2(C)+3(D)−3(E)+5

37.IntheLewisdotstructureX:,whatisthepredictableoxidationnumber?

(A)+1(B)−1(C)+2(D)−2(E)+3

Questions38–40.

(A)Balance(B)Barometer(C)Condenser(D)Funnel(E)Pipette

38.Commonlyusedinthelaboratorytotransferanexactvolumeofliquidfromonecontainertoanother

39.Commonlyusedinthelaboratoryinadistillationsetup

40.Commonlyusedinthelaboratoryinafiltrationsetup

41.Ifyoucollectedhydrogengasbythedisplacementofwaterandundertheconditionsshown:

whichofthefollowingwouldgiveyouthepressureofthehydrogeninthebottle?(A)730.mm−40.8mm(B)730.mm−30.0mm(C)730.mm−30.0mm/13.6+40.8mm(D)730.mm−30.0mm/13.6−40.8mm(E)730.mm−40.8mm/13.6−30.0mm

42.Whatoccurswhenareactionisatequilibriumandmorereactantisaddedtothecontainer?

(A)Theequilibriumremainsunchanged.(B)Theforwardreactionrateincreases.(C)Thereversereactionrateincreases.(D)Theforwardreactionratedecreases.(E)Thereversereactionratedecreases.

43.Howmuchheatenergyisreleasedwhen8gramsofhydrogenareburned?Thethermalequationis2H2(g)+O2(g)→2H2O(g)+483.6kJ.

(A)241.8kJ(B)483.6kJ(C)967.2kJ(D)1,934kJ(E)3,869kJ

44.Wouldaspontaneousreactionoccurbetweenzincionsandgoldatoms?

Zn2++2e−→Zn0E0=−0.76voltAu3++3e−→Au0E0=+1.42volts

(A)yes—Reactionpotential2.18V(B)no—Reactionpotential−2.18V(C)yes—Reactionpotential0.66V(D)no—Reactionpotential−0.66V(E)yes—Reactionpotential0.56V

45.Fourmolesofelectrons(4×6.02×1023electrons)wouldelectroplatehowmanygramsofsilverfromasilvernitratesolution?

(A)108(B)216(C)324(D)432(E)540

46.A5.0MsolutionofHClhashowmanymolesofH+ionin1liter?

(A)0.50(B)1.0(C)2.0(D)2.5(E)5.0

47.WhatistheKspforsilveracetateifasaturatedsolutioncontains2×10−3

molesofsilverion/literofsolution?

(A)2×10−3

(B)2×10−6

(C)4×10−3

(D)4×10−6

(E)4×106

48.ThefollowingdatawereobtainedforH2OandH2S:

Formula Freezing BoilingMass Point(°C) Point(°C)

H2O 18 0 100H2S 34 −83 −60

What is the best explanation for the variation of physical properties

betweenthesetwocompounds?

(A)TheH2Shasstrongerbondsbetweenmolecules.(B)TheH2Ohasagreatdealofhydrogenbonding.(C)Thebondanglesdifferbyabout15°.(D)Theformulamassisofprimeimportance.(E)Theoxygenatomhasasmallerradiusandthuscannotbumpintoother

moleculesasoftenasthesulfur.

49.WhatisthepOHofasolutionthathas0.00001moleofH3O+/literofsolution?

(A)2(B)3(C)4(D)5(E)9

50.Howmanygramsofsulfurarepresentin1moleofH2SO4?

(A)2(B)32(C)49(D)64(E)98

51.Whatistheapproximatemass,ingrams,of1literofnitrousoxide,N2O,atSTP?

(A)1(B)2(C)11.2(D)22(E)44

52.IfthesimplestformulaofasubstanceisCH2anditsmolecularmassis56,whatisitstrueformula?

(A)CH2

(B)C2H4

(C)C3H4

(D)C4H8

(E)C5H10

Questions 53 and 54 refer to the following diagrams of two methods ofcollectinggases:

53.Method1isbestsuitedtocollect

(A)agasdenserthanair(B)agaslessdensethanair(C)agasthatisinsolubleinwater(D)agasthatissolubleinwater(E)agasthathasadistinctcolor

54.Whichofthesegases,becauseofitsdensityandsolubility,shouldbecollectedbyMethod2?

(A)NH3

(B)H2

(C)HCl(D)CO2

(E)He

55.WhatisthemolarmassofCaCO3?

(A)68g/mol(B)75g/mol(C)82g/mol

(D)100g/mol(E)116g/mol

56.Whatvolume,inliters,willbeoccupiedatSTPby4gramsofH2?

(A)11.2(B)22.4(C)33.6(D)44.8(E)56.0

57.HowmanymolesofKOHareneededtoneutralize196gramsofsulfuricacid?(H2SO4=98amu)

(A)1.0(B)1.5(C)2.0(D)4.0(E)6.0

58.Whatvolume,inliters,ofNH3(g)isproducedwhen22.4litersofN2(g)aremadetocombinecompletelywithasufficientquantityofH2(g)underappropriateconditions?

(A)11.2(B)22.4(C)44.8(D)67.2(E)89.6

59.Whatvolume,inliters,ofSO2willresultfromthecompleteburningof64gramsofsulfur?

(A)2.00(B)11.2(C)44.8(D)126(E)158

60.Theamountofenergyrequiredtomelt5.00gramsoficeat0°Cwouldalsoheat1gramofwaterat4°Ctowhatcondition?(Heatoffusion=80cal/gor3.34×102J/g;heatofvaporization=540cal/gor2.26×103J/g)

(A)waterat90°C(B)waterat100°C(C)steamat100°C(D)Partofthewaterwouldbevaporizedtosteam.(E)Allofthewaterwouldbevaporizedtosteam.

61.Howmanymolesofelectronsareneededtoelectroplateadepositof0.5moleofsilverfromasilvernitratesolution?

(A)0.5(B)1(C)27(D)54(E)108

62.AllofthefollowingstatementsaboutcarbondioxidearetrueEXCEPT:

(A)ItcanbepreparedbytheactionofacidonCaCO3.(B)Itisusedinfireextinguishers.(C)Itdissolvesslightlyinwateratroomtemperature.(D)Itsublimesratherthanmeltsat20°Cand1atmpressure.(E)Itisaproductofphotosynthesisinplants.

63.ThreemolesofH2and3molesofI2areintroducedintoaliterboxatatemperatureof490°C.WhatwilltheKexpressionbeforthisreaction?(K=45.9)

64.Ifthefollowingreactionhasachievedequilibriuminaclosedsystem:

N2O4(g) 2NO2(g)

which of the following is (are) increased by decreasing the size of thecontainer?

I.ThevalueofKII.TheconcentrationofN2O4(g)III.Therateofthereversereaction

(A)Ionly(B)IIIonly(C)IandIIonly(D)IIandIIIonly(E)I,II,andIII

65.Whichofthefollowingcorrectlycompletesthisnuclearreaction: +→···+ ?

66.HowmanygramsofNaClwillbeneededtomake100.millilitersof2Msolution?

(A)5.85(B)11.7(C)29.2(D)58.5(E)117

67.HowmanygramsofH2SO4arein1,000.gramsofa10.%solution?(1molofH2SO4=98g)

(A)1.0(B)9.8(C)10.(D)98(E)100.

68.If1moleofethylalcoholin1,000gramsofwaterdepressesthefreezingpointby1.86°Celsius,whatwillbethefreezingpointofasolutionof1moleofethylalcoholin500gramsofwater?

(A)−0.93°C(B)−1.86°C(C)−2.79°C(D)−3.72°C(E)−5.58°C

69.Whichnuclearreactionshowsthereleaseofabetaparticle?

(A)

(B)

(C)

(D)

(E)

Ifyoufinishbeforeonehourisup,youmaygobacktocheckyourworkorcompleteunansweredquestions.

AnswerKeyP R A C T I C E T E S T 4

1.A 14.A 104.T,F2.C 15.A 105.T,T,CE3.E 16.B 106.T,T,CE4.A 17.C 107.T,T,CE5.B 18.D 108.F,T6.C 19.E 109.F,T7.E 20.C 110.T,T,CE8.C 21.E 111.F,T9.B 22.C 112.F,F10.A 23.B 113.T,T,CE11.E 101.T,F 114.F,T12.A 102.T,T,CE 115.T,F13.C 103.T,T,CE 116.T,T,CE

24.C 39.C 54.C25.E 40.D 55.D26.B 41.E 56.D27.E 42.B 57.D28.B 43.C 58.C29.B 44.B 59.C30.B 45.E 60.D31.C 46.E 61.A

32.D 47.D 62.E33.A 48.B 63.D34.C 49.E 64.D35.C 50.B 65.A36.B 51.B 66.B37.C 52.D 67.E38.E 53.C 68.D

69.C

ANSWERSEXPLAINED1.(A)Thevolumeofagasincreasesastemperatureincreasesprovidedthatpressureremainsconstant.Thisisadirectproportion.Heatingaballoonisagoodexample.

2.(C)Thevolumeofagasdecreasesasthepressureisincreasedprovidedthatthetemperatureisheldconstant.Thisisshownbytheinverselyproportionalcurvein(C).Pressureincreaseonaclosedcylinderisagoodexample.

3.(E)Thegraphshowsthatthereisastartingquantityinsolution,andaslightpositiveslopetotherightindicatesadirectlyproportionalchangeinthesolubilityastemperaturerises.

4.(A)Thisisthedefinitionofanymolecule.

5.(B)Acommercialcakemixisamixtureofingredients.

6.(C)Thisisthedefinitionofanisotope.

7.(E)AnacidsaltcontainsoneormoreHatomsinthesaltformulaseparatingapositiveionandthehydrogen-bearingnegativeion.Forexample,Na2SO4isanormalsaltandNaHSO4isanacidsaltbecauseofthepresenceofHinthehydrogensulfateion.InCa(HCO3)2,thesameistrue.Thisisclassifiedasanacidsalt

8.(C)Anatomwithatomicnumber9wouldhavea2,7electronconfiguration,whichmatchestheouterenergylevelofiodine.

9.(B)Thereare2Na,1C,and3O,whichaddto6atoms.

10.(A)pHfrom0to6isacid,7neutral,8to14basic.Mostacidis1.

11.(E)Molarityisdefinedasmolesofsolute/literofsolution.

12.(A)Gasdensitiescanbeexpressedingrams/liter.

13.(C)Molarmassisnotaffectedbypressureandtemperature.

14.(A)Ifthedensityofagasisknown,themassof1Lcanbemultipliedby22.4tofindthemolecularmassbecause1moloccupies22.4LatSTP.

15.(A)BuffersresistchangesinpH.

16.(B)Colorchangeisthefunctionofindicators.

17.(C)OnthepHscale,from0to6isacidand7isneutral.

18.(D)OnthepHscale,from8to14isbasic.

19.(E)Theozone(O3)inthestratosphereabsorbsultravioletraysfromthesun.

20.(C)WhenhydrocarbonscontainingCandHdonothaveenoughoxygentocombustwithO2(g)completely,theproductwillbeCO,carbonmonoxide.

21.(E)2KClO3→2KCl+3O2(g)isthereactionthatoccurs.

22.(C)CO2isslightlysolubleinwater,formingcarbonicacid,H2CO3,whichisaweakacid.

23.(B)SO2thatisfoundintheupperatmosphereisdissolvedinwatermoleculestoformsulfurousacidthatiscorrosiveacidrain.

101.(T,F)Theassertionistrue,butthedegreeofmotionofgasmoleculesisdirectlyrelatedtothetemperature.

102.(T,T,CE)Assertionandreasonaretrue;anelectroncanbetreatedaseitheranelectromagneticwaveorabundleofnegativecharge.

103.(T,T,CE)Ahomologousseriesincreaseseachmemberbyaconstantnumberofcarbonsandhydrogens.Examplesarethealkane,alkene,andalkyneseries,whicheachincreasethechainbyaCH2group.Thereasonistrueanddoesexplaintheassertion.

104.(T,F)Thenuclearchargeofanactivemetallicionisgreaterthanthatoftheelectroncloud.Thereasonisfalse.

105.(T,T,CE)Anegativeheatofformationindicatesthatthereactionisexothermicandtheenthalpychangeisnegative.

106.(T,T,CE)Waterisapolarmoleculebecausethereisunequalsharingofbondingelectrons.

107.(T,T,CE)Thisisafunctionofacatalyst—tospeedupareactionwithoutpermanentlychangingitself.Assertionandreasonaretrue.

108.(F,T)TheCuislosingelectronsandthusbeingoxidized;theassertionisfalse.Itisfurnishingelectronsandthusisareducingagent;thereasonistrue.

109.(F,T)H2=2,He=4(molecularmass);theninversely istherateofdiffusionofhydrogentohelium.Theassertionisfalse;thereason,true.

110.(T,T,CE)Sincethegasisbeingheatedatconstantpressure,itexpands.Thetemperaturesareconvertedtokelvins(K)byadding2730totheCelsiusreadings.Thefractionmustbe andthiswillincreasethevolume.

111.(F,T)Gibbsfreeenergyisusefulinindicatingtheconditionsunderwhichachemicalreactionwilloccur.Itisnotrelatedtosolubility.Itistruethat,generallyspeaking,solubilityofasoluteincreaseswithanincreaseinthetemperatureofthesolvent.

112.(F,F)Wateris hydrogenand oxygenbyweight.Bothassertionandreasonarefalse.

113.(T,T,CE)Fourgramsoficewouldrequire4×80cal/g=320calor4×3.34×102J/g=1.34×103Jtomelttheice.

114.(F,T)Thereactionis:2H2+O2→2H2O.Thecoefficientsofthisgaseousreactionshowthat2litersofhydrogenreactwith1literofoxygen.Thiswouldleave1literofunreactedoxygen.Thelimitingfactoristhehydrogen.

115.(T,F)Thereasonwhywaterisagoodsolventisfalse.

116.(T,T,CE)ThedensityofagasatSTPisfoundbydividingthemolecularmassby22.4L.NH3hasagram-molecularmassofN=14+3H=3oratotalof17g.Thegram-molecularmassofAris40g.Thedensityofeachcanbefoundbydividingby22.4L,butobviouslythedensityoftheammoniawillbesmaller.

24.(C)Theenergynecessarytogetthereactionstarted,whichistheactivationenergy,isshownatC.

25.(E)2KClO3→2KCl+3O2(g)showsthat2.00molofKClO3yield3molofO2.

26.(B)Acatalystcanspeedupareactionbyloweringtheactivationenergyneededtostartthereactionandthenkeepitgoing.

27.(E)Theatomicnumbergivesthenumberofprotonsinthenucleusandthetotalnumberofelectrons.Themassnumberindicatesthetotalnumberofprotonsandneutronsinthenucleus—forNa,23(11protons+12neutrons).

28.(B) .Forgasesthisisexpressedasgramsperliter.Since1

gram-molecularmassofagasoccupies22.4L,17g/22.4L=0.76g/L.

29.(B)ChoiceIIIismadeupofelementsfromextremesidesofthePeriodicTableandwillthereforeformionicbonds.

30.(B)OnlyIIIisaringhydrocarbonofthearomaticseries.

31.(C)SinceLiishigherinGroup1thanNa,andKishigherthanCs,theyhavesmallerradiiandhencehigherionizationenergies.AlistotherightofNaandthereforehasahigherionizationenergy.

32.(D)OnlyIIandIIIarecorrectlybalanced.Tobecorrect,Ishouldhaveonly3e−.Equationsmustbebalancedforbothnumbersofatomsandcharge.

36.(B)Thisorbitalconfigurationshows6electronsinthethirdenergylevel.Theatomwouldliketogain2e−tofillthe3pandtherebygaina−2oxidationnumber.

37.(C)Withthisstructure,theatomwouldtendtolosetheseelectronsandgeta+2charge.

38.(E)Thepipetteisusedtotransferliquidfromonecontainertoanother.

39.(C)Thecondensertubeisusedindistillation.

40.(D)Thefunnelisusedtoholdthefilterpaper.

41.(E)ThepressureinthebottlewouldbelessthanatmosphericpressurebytheHgequivalentheightofthe30mmofwaterabovethelevelinthecollectingpan.Thisiscalculatedas40.8mmwater/(13.6mmwater/1mmHg)andmustbesubtractedfromatmosphericpressure.Theotheradjustmentistosubtractthevaporpressureofwaterthatisinthehydrogengassinceitwascollectedoverwater.Thispressureisgivenas30.0mmHg.Subtractingeachofthesefrom730.mmHg,thegivenatmosphericpressure,youhave730.mm−40.8mm/13.6−30.0mm.

42.(B)Theequilibriumshiftsinthedirectionthattendstorelievethestressandthusregainequilibrium.

43.(C)Thethermalreactionshows2molofhydrogenreacting,or4g.Therefore,8gwouldreleasetwicetheamountofenergy:

2×483.6kJ=967.2kJ.

44.(B)Thereactionpotentialcalculationwouldbe:

Note:ThestandardpotentialsarenotmultipliedbythecoefficientsincalculatingtheE0forthereaction.

45.(D)SinceAg++1e−→Ag°,1molofelectronsyields1molofsilver;1molsilver=6.02×1023atoms4×108g/mol=432g

46.(E)5.0M= andsinceHClionizescompletelytherewouldbe5.0

molofH+and5.0molofCl−ions.

47.(D)Ksp=[Ag+][C2H3O2−]=[2×10−3][2×10−3]

(Since

AgC2H3O2 Ag++C2H3O2−

thesilverionandacetateionconcentrationsareequal.)

Ksp=4×10−6

48.(B)Itistheexplanationfortheobservedhighboilingpointandhighfreezingpointofwatercomparedwithhydrogensulfide.

49.(E)pH=−log[H+]=−log[10−5]=−[−5]=5

SincepH+pOH=14,pOH=14−5=9.

50.(B)1molH2SO4contains1molarmassofsulfur,thatis,32g.

51.(B)N2O=44g/mol

(2×14+16=44)

1molofagasoccupies22.4L,so44g/22.4L=1.99g/L.

52.(D)CH2=14

(12+2=14molecularmass)56÷14=4Then4×CH2=C4H8

53.(C)Onlyinsolublegasescanbecollectedinthisway.

54.(C)HClisverysolubleinwateranddenserthanair,soitissuitedtotheNo.2collectionmethod.

55.(D)Ca=40C=12

56.(D)Gram-molecularmassofH2is2g.4gis2mol,andeachmoleoccupies22.4L.2×22.4=44.8L.

57.(D)

Thenx=4.0mol.

58.(C)

Thenx=44.8L.

59.(C)

Thenx=44.8L.

60.(D)5.00gicetowater=5.00×80cal=400cal.1gat4°cangoto100°Caswaterandabsorb1cal/°C.Then400cal−(100°−4°)=400−96=304cal.304calcanchange or0.56gofwatertosteam.There

obviouslyisnotenoughheattovaporizeallthewater.Ifdoneinjoules,5.00goficetowater=5.00×3.34×102g/J=1.67×103J.

1gat4°Cto100°C= temp=96°96°×4.18J/g/°C=17.3J/g=1.73×101J=0.0173×103J1.67×103J−0.0173×103J=1.65×103Jleftforvaporization.Since1grequires2.26×103Jforvaporization,(D)istheanswer.

61.(A)SinceAg+gains1e−tobecomeAg0,0.5molrequires0.5molofelectrons.

62.(E)CO2isareactantinphotosynthesis,notaproduct.Thereactionis

or

63.(D)

Letx=molesofH2andalsoofI2thatcombinetoformHI.Thenatequilibrium[H2]=3-x,[I2]=3-x,[HI]=2x.

64.(D)Inaclosedsystem,decreasingthesizeofthecontainerwillcausethepressuretoincrease.Whenpressureisappliedtoanequilibriuminvolvinggases,thereactionthatlowersthepressurebydecreasingthenumberofmoleculeswillincreaseinrate.Inthisreaction,therateofthereversereaction,inwhich2moleculesaredecreasedto1,increases,thusreducingpressurewhilealsoincreasingtheconcentrationofN2O4.Thus,IIandIIIaretrue.

65.(A)ThisisRutherford’sfamousartificialtransmutationexperiment,donein1919.

66.(B)

2molofNaCl=2×58.5g=117.0g2M=117g/1,000mL,

x=11.7g

67.(E)Percentisbymass,so10.%is0.10×1,000.gor100.g.

68.(D)Firstfindthemolality.1molin500g=2molin1,000g.Then2×1.86°C=3.72°Cdropfrom0°Cor-3.72°C,thenewfreezingpoint.

69.(C)Thenuclearreactionsshownrelease:(A)aneutron,(B)analphaparticle,(C)abetaparticle,(D)noparticles,(E)apositron.

CALCULATINGYOURSCOREYour scoreonPracticeTest4 cannowbe computedmanually.Theactual testwill be scored bymachine, but the samemethod is used to arrive at the rawscore.Yougetonepoint foreachcorrectanswer.Foreachwronganswer,youloseone-fourthofapoint.Questions thatyouomitor thathavemorethanoneanswerarenotcounted.Onyouranswersheetmarkallcorrectanswerswitha“C”andallincorrectanswerswithan“X”.

DeterminingYourRawTestScoreTotalthenumberofcorrectanswersyouhaverecordedonyouranswersheet.ItshouldbethesameasthetotalofallthenumbersyouplaceintheblockinthelowerleftcornerofeachareaoftheSubjectAreasummaryinthenextsection.

A.Enterthetotalnumberofcorrectanswershere:________Nowcountthenumberofwronganswersyourecordedonyouranswersheet.

B.Enterthetotalnumberofwronganswershere:________MultiplythenumberofwronganswersinBby0.25.

C.Enterthatproducthere:________SubtracttheresultinCfromthetotalnumberofrightanswersinA.

D.Entertheresultofyoursubtractionhere:________

E.RoundtheresultinDtothenearestwholenumber:________.Thisisyourrawtestscore.

ConversionofRawScorestoScaledScoresYour raw score is converted by the College Board into a scaled score. TheCollegeBoardscoresrangefrom200to800.ThisconversionisdonetoensurethatascoreearnedonanyeditionofaparticularSATSubjectTestinChemistryiscomparabletothesamescaledscoreearnedonanyothereditionofthesametest.Becausesomeeditionsofthetestsmaybeslightlyeasierormoredifficultthan others, scaled scores are adjusted so that they indicate the same level of

performance regardless of the edition of the test taken and the ability of thegroup that takes it. Consequently, a specific raw score on one edition of aparticulartestwillnotnecessarilytranslatetothesamescaledscoreonanothereditionofthesametest.Becausethepracticetestsinthisbookhavenolargepopulationofscoreswith

whichtheycanbescaled,scaledscorescannotbedetermined.Results from previous SAT Chemistry tests appear to indicate that the

conversionofrawscorestoscaledscoresGENERALLYfollowsthispattern:

Note that this scale provides only a general idea of what a raw score maytranslateintoonascaledscorerangeof800–200.Scalingoneverytestisusuallyslightly different. Some students who had taken the SAT Subject Test inChemistry after using this book had reported that they have scored slightlyhigherontheSATtestthanonthepracticetestsinthisbook.Theyallreportedthatpreparingwellforthetestpaidoffinabetterscore!

DIAGNOSINGYOURNEEDSAftertakingPracticeTest4,checkyouranswersagainstthecorrectones.Thenfillinthechartbelow.Inthespaceundereachquestionnumber,placeacheckifyouansweredthat

questioncorrectly.

EXAMPLE:

Ifyouranswertoquestion5wascorrect,placeacheckintheappropriatebox.Next, total the check marks for each section and insert the number in the

designatedblock.Nowdo thearithmetic indicated, and insertyourpercent foreacharea.

*Thesubjectareashavebeenexpandedtoidentifyspecificareasinthetext.

*Thesubjectareashavebeenexpandedtoidentifyspecificareasinthetext.

APPENDIXES

ModernPeriodicTable

SomeImportantEquations

Density(d)

PercentError

Percenterror=

PercentYield

Percentyield=

PercentageComposition

Percentagecompositionbymass=

Boyle’sLaw

P1V1=P2V2

PV=

Charles’sLaw

V1T2=V2T1

Dalton’sLawofPartialPressures

PT=pa+pb+pc+...

IdealGasLaw

PV=nRT

CombinedGasLaw

Graham’sLawofEffusion

GeneralEquationforEquilibriumConstantoftheEquation

aA+bB cC+dD

EquilibriumConstantforWater

Kw=[H1][OH1]=1×10−14

Molarity(M)

Molarity=

Titration

MaVa=MbVb(a=acid,b=base)

Molality(m)

Molality=

Dilution

M1V1=M2V2

BoilingPointElevation

ΔTb=Kbm

whereKbisthemolalboiling-point-elevationconstant

FreezingPointDepression

ΔTf=Kfm

whereKfisthemolalfreezingpointdepressionconstant

RateofReaction

Rate= [A]x[B]y

where[A]and[B]aremolarconcentrationsofreactants,and isarateconstant

Hess’sLaw

ΔHnet=ΔH1+ΔH2

EntropyChange

ΔS=Sproducts–Sreactants

GibbsFreeEnergy

ΔG=ΔH–TΔS

SomeUsefulTables

TheChemicalElements

(Atomicmasses in this tablearebasedon theatomicmassofcarbon-12beingexactly12.)

*Anumberinparenthesesisthemassnumberofthemoststableisotope.

Glossary

(SeeIndexforadditionalreferences)

absolutetemperatureTemperaturemeasuredontheabsolutescale,whichhasitsoriginatabsolutezero.SeealsoKelvinscale.

absorptionTheprocessoftakingupbycapillary,osmotic,chemical,orsolventaction,asaspongeabsorbswater.

acidAwatersolutionthathasanexcessofhydrogenions;anacidturnslitmuspaperpinkorred,hasasourtaste,andneutralizesbasestoformsalts.

acidicanhydrideAnonmetallicoxidethat,whenplacedinwater,reactstoformanacidsolution.

acidsaltAsaltformedbyreplacingpartofthehydrogenionsofadibasicortribasicacidwithmetallicions.Examples:NaHSO4,NaH2PO4.

actinideseriesTheseriesofradioactiveelementsstartingwithactinium,No.89,andendingwithlawrencium,No.103.

activatedcharcoalAspeciallytreatedandfinelydividedformofcarbon,whichpossessesahighdegreeofadsorption.

activationenergyTheminimumenergynecessarytostartareaction.adsorptionTheadhesion(inanextremelythinlayer)ofthemoleculesofgases,ofdissolvedsubstances,orofliquidstothesurfacesofsolidorliquidbodieswithwhichtheycomeintocontact.

alcoholAnorganichydroxylcompoundformedbyreplacingoneormorehydrogenatomsofahydrocarbonwithanequalnumberofhydroxyl(OH)groups.

aldehydeAnorganiccompoundformedbydehydratingoxidizedalcohol;containsthecharacteristic—CHOgroup.

alkaliUsually,astrongbase,suchassodiumhydroxideorpotassiumhydroxide.alkalineReferringtoanysubstancethathasbasicproperties.alkylAsubstitutentobtainedfromasaturatedhydrocarbonbyremovingone

hydrogenatom.Examples:methyl(CH3

−),ethyl(C2H5−).

allotropicformsFormsofthesameelementthatdifferintheircrystallinestructures.

alloyAsubstancecomposedoftwoormoremetals,whichareintimatelymixed;usuallymadebymeltingthemetalstogether.

alphaparticlesPositivelychargedheliumnuclei.amineAcompoundsuchasCH3NH2,derivedfromammoniabysubstitutingoneormorehydrocarbonradicalsforhydrogenatoms.

aminoacidOneofthe“buildingblocks”ofproteins;containsoneormoreNH2

−groupsthathavereplacedthesamenumberofhydrogenatomsinanorganicacid.

amorphousHavingnodefinitecrystallinestructure.amphotericReferringtoahydroxidethatmayhaveeitheracidicorbasicproperties,dependingonthesubstancewithwhichitreacts.

analysisThebreakingdownofacompoundintotwoormoresimplersubstances.

anhydrideAcompoundderivedfromanothercompoundbytheremovalofwater;itwillcombinewithwatertoformanacid(acidicanhydride)orabase(basicanhydride).

anhydrousContainingnowater.anionAnionorparticlethathasanegativechargeandthusisattractedtoapositivelychargedanode.

anodeTheelectrodeinanelectrolyticcellthathasapositivechargeandattractsnegativeions.

antichlorAsubstanceusedtoremovetheexcessofchlorineinthebleachingprocess.

aromaticcompoundAcompoundwhosebasicstructurecontainsthebenzenering;itusuallyhasanodor.

atmosphereThelayerofgasessurroundingtheearth;also,aunitofpressure(1atm=approx.760mmofHgortorr).

atomThesmallestparticleofanelementthatretainsthepropertiesofthatelementandcanenterintoachemicalreaction.

atomicenergySeenuclearenergy,amoreaccurateterm.atomicmass(relativeatomicmassoratomicweight)Theaveragemeanvalueoftheisotopicmassesoftheatomsofanelement.Itindicatestherelativemassoftheelementascomparedwiththatofcarbon-12,whichisassignedamassofexactly12atomicmassunits.

atomicmassunitOnetwelfthofthemassofacarbon-12atom;equivalentto1.660531×10−27kilogram(abbreviation:amuorμ).

atomicnumberThenumberthatindicatestheorderofanelementintheperiodicsystem;numericallyequaltothenumberofprotonsinthenucleusoftheatom,orthenumberofnegativeelectronslocatedoutsidethenucleusoftheatom.

atomicradiusOne-halfthedistancebetweenadjacentnucleiinthecrystallineorsolidphaseofanelement;thedistancefromtheatomicnucleustothevalenceelectrons.

atomicweightSeeatomicmass.AufbauPrincipleTheprinciplethatstatesthatanelectronoccupiesthelowestenergyorbitalthatcanreceiveit.

Avogadro’shypothesisSeeunderlaws.Avogadro’snumberThenumberofmoleculesin1gram-molecularvolumeofasubstance,orthenumberofatomsin1gram-atomicmassofanelement;equalto6.022169×1023.Seealsomole.

barometerAninstrument,inventedbyTorricelliin1643,usedformeasuringatmosphericpressure.

baseAwatersolutionthatcontainsanexcessofhydroxideions;aprotonacceptor;abaseturnslitmuspaperblueandneutralizesacidstoformsalts.

basicanhydrideAmetallicoxidethatformsabasewhenplacedinwater.betaparticlesHigh-speed,negativelychargedelectrons or emittedinradiation.

binaryReferringtoacompoundcomposedoftwoelements,suchasH2O.

boilingpointThetemperatureatwhichthevaporpressureofaliquidequalstheatmosphericpressure.

bondenergyTheenergyneededtobreakachemicalbondandformaneutralatom.

bondingTheunionofatomstoformcompoundsormoleculesbyfillingtheiroutershellsofelectrons.Thiscanbedonethroughgivingandtakingelectrons(ionic)orbysharingelectrons(covalent).

Boyle’sLawSeeunderlaws.brassAnalloyofcopperandzinc.breederreactorAnuclearreactorinwhichmorefissionablematerialisproducedthanisusedupduringoperation.

BrownianmovementContinuouszigzaggingmovementofcolloidalparticlesinadispersingmedium,asviewedthroughanultramicroscope.

bufferAsubstancethat,whenaddedtoasolution,makeschangingthepHofthesolutionmoredifficult.

calorieAunitofheat;theamountofheatneededtoraisethetemperatureof1gramofwater1degreeontheCelsiusscale.

calorimeterAninstrumentusedtomeasuretheamountofheatliberatedorabsorbedduringachange.

carbonatedwaterWatercontainingdissolvedcarbondioxide.carbondatingTheuseofradioactivecarbon-14toestimatetheagesofancientmaterials,suchasarcheologicalorpaleontologicalspecimens.

catalystAsubstancethatspeedsuporslowsdownareactionwithoutbeingpermanentlychangeditself.

cathodeTheelectrodeinanelectrolyticcellthatisnegativelychargedandattractspositiveions.

cathoderaysStreamsofelectronsgivenoffbythecathodeofavacuumtube.cationAnionthathasapositivecharge.CelsiusscaleAtemperaturescaledividedinto100equaldivisionsandbasedonwaterfreezingat0°andboilingat100°.Synonymouswithcentigrade.

chainreactionAreactionproducedduringnuclearfissionwhenatleastoneneutronfromeachfissionproducesanotherfission,sothattheprocessbecomesself-sustainingwithoutadditionalexternalenergy.

Charles’sLawSeeunderlaws.chemicalchangeAchangethatalterstheatomicstructuresofthesubstancesinvolvedandresultsindifferentproperties.

chemicalpropertyApropertythatdetermineshowasubstancewillbehaveinachemicalreaction.

chemistryThescienceconcernedwiththecompositionsofsubstancesandthechangesthattheyundergo.

colligativepropertyApropertyofasolutionthatdependsprimarilyontheconcentration,notthetype,ofparticlespresent.

colloidsParticleslargerthanthosefoundinasolutionbutsmallerthanthoseinasuspension.

CombiningVolumesSeeGay-Lussac’s,underlaws.combustionAchemicalactioninwhichbothheatandlightaregivenoff.compoundAsubstancecomposedofelementschemicallyunitedindefiniteproportionsbyweight.

condensation(a)Achangefromgaseoustoliquidstate;(b)theunionoflikeorunlikemoleculeswiththeeliminationofwater,hydrogenchloride,oralcohol.

ConservationofEnergySeeunderlaws.ConservationofMatterSeeunderlaws.controlrodInanuclearreactor,arodofacertainmetalsuchascadmium,whichcontrolsthespeedofthechainreactionbyabsorbingneutrons.

coordinatecovalenceCovalenceinwhichbothelectronsinapaircomefromthesameatom.

covalentbondingBondingaccomplishedthroughthesharingofelectronssothatatomscanfilltheiroutershells.

criticalmassThesmallestamountoffissionablematerialthatwillsustainachainreaction.

criticaltemperatureThetemperatureabovewhichnogascanbeliquefied,

regardlessofthepressureapplied.crystallineHavingadefinitemolecularorionicstructure.crystallizationTheprocessofformingdefinitelyshapedcrystalswhenwaterisevaporatedfromasolutionofthesubstance.

cyclotronAdeviceusedtoacceleratechargedparticlestohighenergiesforbombardingthenucleiofatoms.

Dalton’sLawofPartialPressuresSeeunderlaws.decompositionThebreakingdownofacompoundintosimplersubstancesorintoitsconstituentelements.

DefiniteCompositionSeeunderlaws.dehydrateTotakewaterfromasubstance.dehydratingagentAsubstanceabletowithdrawwaterfromanothersubstance,therebydryingit.

deliquescenceTheabsorptionbyasubstanceofwaterfromtheair,sothatthesubstancebecomeswet.

denaturedalcoholEthylalcoholthathasbeen“poisoned”inordertoproduce(byavoidingfederaltax)acheaperalcoholforindustrialpurposes.

densityThemassperunitvolumeofasubstance;themathematicalformulaisD=m/V,whereD=density,m=mass,andV=volume.

destructivedistillationTheprocessofheatinganorganicsubstance,suchascoal,intheabsenceofairtobreakitdownintosolidandvolatileproducts.

deuteriumAnisotopeofhydrogen,sometimescalledheavyhydrogen,withanatomicweightof2.

dewpointThehighesttemperatureatwhichwatervaporcondensesoutoftheair.

dialysisTheprocessofseparationofasolutionbydiffusionthroughasemipermeablemembrane.

diffusionTheprocesswherebygasesorliquidsinterminglefreelyoftheirownaccord.

dipole-dipoleattractionArelativelyweakforceofattractionbetweenpolar

molecules;acomponentofvanderWaalsforces.displacementAchangebywhichanelementtakestheplaceofanotherelementinacompound.

dissociation(ionic)Theseparationoftheionsofanioniccompoundduetotheactionofasolvent.

distillationTheprocessoffirstvaporizingaliquidandthencondensingthevaporbackintoaliquid,leavingbehindthenonvolatileimpurities.

doublebondAbondbetweenatomsinvolvingtwoelectronpairs.Inorganicchemistry:unsaturated.

doubledisplacementAreactioninwhichtwochemicalsubstancesexchangeionswiththeformationoftwonewcompounds.

dryiceSolidcarbondioxide.ductileCapableofbeingdrawnintothinwire.

effervescenceTherapidescapeofexcessgasthathasbeendissolvedinaliquid.efflorescenceThelossbyasubstanceofitswaterofhydrationonexposuretoairatordinarytemperatures.

effusionTheflowofagasthroughasmallaperture.

EinsteinequationE=mc2,whichrelatesmasstoenergy;E=energyinergs,m=massingrams,andc=velocityoflight,3×1010centimeters/second.

electrodeAterminalofanelectrolyticcell.electrodepotentialThedifferenceinpotentialbetweenanelectrodeandthesolutioninwhichitisimmersed.

electrolysisTheprocessofseparatingtheionsinacompoundbymeansofelectricallychargedpoles.

electrolyticcellAcellinwhichelectrolysisiscarriedout.electrolyteAliquidthatwillconductanelectriccurrent.electronAnegativelychargedparticlefoundoutsidethenucleusoftheatom;ithasamassof9.109×10−28gram.

electrondotsymbolSeeLewisdotsymbol.

electronegativityThenumericalexpressionoftherelativestrengthwithwhichtheatomsofanelementattractvalenceelectronstothemselves;thehigherthenumber,thegreatertheattraction.

electronvoltAunitforexpressingthekineticenergyofsubatomicparticles;theenergyacquiredbyanelectronwhenitisacceleratedbyapotentialdifferenceof1volt;equals1.6×10−12ergor23.1kilocalories/mole(abbreviation:eV).

electroplatingDepositingathinlayerof(usually)ametallicelementonthesurfaceofanothermetalbyelectrolysis.

elementOneofthemorethan100“buildingblocks”ofwhichallmatteriscomposed.Anelementconsistsofatomsofonlyonekindandcannotbedecomposedfurtherbyordinarychemicalmeans.

empiricalformulaAformulathatshowsonlythesimplestratioofthenumbersandkindsofatoms,suchasCH4.

emulsifyingagentAcolloidalsubstancethatformsafilmabouttheparticlesoftwoimmiscibleliquids,sothatoneliquidremainssuspendedintheother.

emulsionAsuspensionoffineparticlesordropletsofoneliquidinanother,thetwoliquidsbeingimmiscibleineachother;thedropletsaresurroundedbyacolloidal(emulsifying)agent.

endothermicReferringtoachemicalreactionthatresultsinanoverallabsorptionofheatfromitssurroundings.

energyThecapacitytodowork.Ineverychemicalchangeenergyiseithergivenoffortakenin.Formsofenergyareheat,light,motion,sound,andelectrical,chemical,andnuclearenergy.

enthalpyTheheatcontentofachemicalsystem.entropyThemeasureoftherandomnessordisorderthatexistsinasystem.equationAshorthandmethodofshowingthechangesthattakeplaceinachemicalreaction.

equilibriumThepointinareversiblereactionatwhichtheforwardreactionisoccurringatthesamerateastheopposingreaction.

ergAunitofenergyorworkdonebyaforceof1dyne(1/980gofforce)actingthroughadistanceof1centimeter;equals2.4×10−11kilocalorie.

esterAnorganicsaltformedbythereactionofanalcoholwithanorganic(or

inorganic)acid.esterificationAchemicalreactionbetweenanalcoholandanacid,inwhichanesterisformed.

etherAnorganiccompoundcontainingthe–O–group.eudiometerAgraduatedglasstubeintowhichgasesareplacedandsubjectedtoanelectricspark;usedtomeasuretheindividualvolumesofcombininggases.

evaporationTheprocessinwhichmoleculesofaliquid(orasolid)leavethesurfaceintheformofvapor.

exothermicReferringtoachemicalreactionthatresultsinthegivingoffofheattoitssurroundings.

FahrenheitscaleThetemperaturescalethathas32°asthefreezingpointofwaterand212°astheboilingpoint.

falloutTheresidualradioactivityfromanatmosphericnucleartest,whicheventuallysettlesonthesurfaceoftheearth.

Faraday’sLawSeeunderlaws.filtrationTheprocessbywhichsuspendedmatterisremovedfromaliquidbypassingtheliquidthroughaporousmaterial.

FirstLawofThermodynamicsSeeunderlaws.fissionAnuclearreactionthatreleasesenergybecauseofthesplittingoflargenucleiintosmallerones.

fixationofnitrogenAnyprocessforconvertingatmosphericnitrogenintocompounds,suchasammoniaandnitricacid.

flameTheglowingmassofgasandluminousparticlesproducedbytheburningofagaseoussubstance.

flammableCapableofbeingeasilysetonfire;combustible(sameasinflammable).

fluorescenceEmissionbyasubstanceofelectromagneticradiation,usuallyvisible,astheimmediateresultof(andonlyduring)absorptionofenergyfromanothersource.

fluoridationAdditionofsmallamountsoffluoride(usuallyNaF)todrinking

watertohelppreventtoothdecay.fluxInmetallurgy:asubstancethathelpstomeltandremovethesolidimpuritiesasslag.Insoldering:asubstancethatcleansthesurfaceofthemetaltobesoldered.Innucleonics:theconcentrationofnuclearparticlesorrays.

formulaAnexpressionthatusesthesymbolsforelementsandsubscriptstoshowthebasicmakeupofasubstance.

formulamassThesumoftheatomicmassunitsofalltheatoms(orions)containedinaformula.

fractionalcrystallizationTheseparationofthecomponentsinamixtureofdissolvedsolidsbyevaporationaccordingtoindividualsolubilities.

fractionaldistillationTheseparationofthecomponentsinamixtureofliquidshavingdifferentboilingpointsbyvaporization.

freeenergySeeGibbsfreeenergy.freezingpointThespecifictemperatureatwhichagivenliquidanditssolidformareinequilibrium.

fuelAnysubstanceusedtofurnishheatbycombustion.Seealsonuclearfuel.fuelcellAdeviceforconvertinganordinaryfuelsuchashydrogenormethanedirectlyintoelectricity.

functionalgroupAgroupofatomsthatcharacterizescertaintypesoforganiccompounds,suchas—OHforalcohols,andthatreactsmoreorlessindependently.

fusionAnuclearreactionthatreleasesenergybecauseoftheunionofsmallernucleitoformlargerones.

fusionmeltingChangingasolidtotheliquidstatebyheating.

galvanizingApplyingacoatingofzinctoironorsteeltoprotectthelatterfromrusting.

gammaraysAtypeofradiationconsistingofhigh-energywavesthatcanpassthroughmostmaterials.Symbol:γ

gasAphaseofmatterthathasneitherdefiniteshapenordefinitevolume.Gay-Lussac’sLawSeeunderlaws.

GibbsfreeenergyChangesinGibbsfreeenergy, G,areusefulinindicatingtheconditionsunderwhichachemicalreactionwilloccur.Theequationis G= H-T S,where H=changeinenthalpyand S=changeinentropy.IfGisnegative,thereactionwillproceedspontaneouslytoequilibrium.

glassAnamorphous,usuallytranslucentsubstanceconsistingofamixtureofsilicates.Ordinaryglassismadebyfusingtogethersilicaandsodiumcarbonateandlime;thevariousformsofglasscontainmanyothersilicates.

Graham’sLawSeeunderlaws.gramAunitofweightinthemetricsystem;theweightof1milliliterofwaterat4°C(abbreviation:

g).gram-atomicmassTheatomicmass,ingrams,ofanelement.gram-formulaweightTheformulaweight,ingrams,ofasubstance.groupAverticalcolumnofelementsintheperiodictablethatgenerallyhavesimilarproperties.

half-lifeThetimerequiredforhalfofthemassofaradioactivesubstancetodisintegrate.

half-reactionOneofthetwoparts,eitherthereductionpartortheoxidationpart,ofaredoxreaction.

halogenAnyofthefivenonmetallicelements(fluorine,chlorine,bromine,iodine,astatine)thatformpartofGroup17ofthePeriodicTable.

heatAformofmolecularenergy;itpassesfromawarmerbodytoacoolerone.heatcapacity(specificheat)Thequantityofheat,incalories,neededtoraisethetemperatureof1gramofasubstance1degreeontheCelsiusscale.

heatofformationThequantityofheateithergivenofforabsorbedintheformationof1moleofasubstancefromitselements.

heatoffusionTheamountofheat,incalories,requiredtomelt1gramofasolid;forwater,80calories.

heatofvaporizationThequantityofheatneededtovaporize1gramofaliquidatconstanttemperatureandpressure;forwaterat100°C,540calories.

heavywater(deuteriumoxide,D2O)Waterinwhichthehydrogenatomsarereplacedbyatomsoftheisotopeofhydrogen,deuterium.

Henry’sLawSeeunderlaws.Hess’sLawSeeunderlaws.homogeneousUniform;havingeveryportionexactlylikeeveryotherportion.homologousAlikeinstructure;referringtoseriesoforganiccompounds,suchashydrocarbons,inwhicheachmemberdiffersfromthenextbytheadditionofthesamegroup.

humidityTheamountofmoistureintheair.hybridizationThecombinationoftwoormoreorbitalstoformneworbitals.hydrateAcompoundthathaswatermoleculesincludedinitscrystallinemakeup.

hydrideAnybinarycompoundcontaininghydrogen,suchasHCl.hydrogenationAprocessinwhichhydrogenismadetocombinewithanothersubstance,usuallyorganic,inthepresenceofacatalyst.

hydrogenbondAweakchemicallinkagebetweenthehydrogenofonepolarmoleculeandtheoppositelychargedportionofacloselyadjacentmolecule.

hydrolysisOfcarbohydrates:theactionofwaterinthepresenceofacatalystupononecarbohydratetoformsimplercarbohydrates.Ofsalts:areactioninvolvingthesplittingofwaterintoitsionsbytheformationofaweakacid,aweakbase,orboth.

hydroniumionAhydratedion,H2O·H+orH3O+.

hydroponicsGrowingplantswithouttheuseofsoil,asinnutrientsolutionorinsandirrigatedwithnutrientsolution.

hydroxylReferringtothe—OHradical.hygroscopicReferringtotheabilityofasubstancetodrawwatervaporfromtheatmospheretoitselfandbecomewet.

hypothesisApossibleexplanationofthenatureofanactionorphenomenon;ahypothesisisnotascompletelydevelopedasatheory.

IdealGasLawSeeunderlaws.

immiscibleReferringtotheinabilityoftwoliquidstomix.indicatorAdyethatshowsonecolorinthepresenceofthehydrogenion(acid)andadifferentcolorinthepresenceofthehydroxylion(base).

inertiaThepropertyofmatterwherebyitremainsatrestor,ifinmotion,remainsinmotioninastraightlineunlessacteduponbyanoutsideforce.

ionAnatomoragroupofcombinedatomsthatcarriesoneormoreelectriccharges.Examples:NH4

+,OH−.

ionicbondingThebondingofionsduetotheiroppositecharges.ionicequationAnequationshowingareactionamongions.ionizationTheprocessinwhichionsareformedfromneutralatoms.ionizationequationAnequationshowingtheionssetfreefromanelectrolyte.isomerizationTherearrangementofatomsinamoleculetoformisomers.isomersTwoormorecompoundshavingthesamepercentagecompositionbutdifferentarrangementsofatomsintheirmoleculesandhencedifferentproperties.

isotopesTwoormoreformsofanelementthatdifferonlyinthenumberofneutronsinthenucleusandhenceintheirmassnumbers.

IUPACInternationalUnionofPureandAppliedChemistry,anorganizationthatestablishesstandardrulesfornamingcompounds.

jouleTheSIunitofworkorofenergyequaltoworkdone;1joule=0.2388calorie;1calorie=4.18

joule.

KelvinscaleAtemperaturescalebasedonwaterfreezingat273andboilingat373Kelvinunits;itsoriginisabsolutezero.Synonymouswithabsolutescale.

kernel(atomic)Thenucleusandalltheelectronshellsofanatomexcepttheouterone;usuallydesignatedbythesymbolfortheatom.

ketoneAnorganiccompoundcontainingthe—CO—group.kilocalorieAunitofheat;theamountofheatneededtoraisethetemperatureof

1kilogramofwater1degreeontheCelsiusscale.kindlingtemperatureThetemperaturetowhichagivensubstancemustberaisedbeforeitignites.

Kinetic-MolecularTheoryThetheorythatallmoleculesareinmotion;thismotionismostrapidingases,lessrapidinliquids,andveryslowinsolids.

lanthanideseriesThe“rareearth”seriesofelementsstartingwithlanthanum,No.57,andendingwithlutetium,No.71.

law(inscience)Ageneralizedstatementabouttheuniformbehaviorinnaturalprocesses.

lawsAvogadro’sEqualvolumesofgasesunderidenticalconditionsoftemperatureandpressurecontainequalnumbersofparticles(atoms,molecules,ions,orelectrons).

Boyle’sThevolumeofaconfinedgasisinverselyproportionaltothepressuretowhichitissubjected,providedthatthetemperatureremainsthesame.

Charles’sThevolumeofaconfinedgasisdirectlyproportionaltotheabsolutetemperature,providedthatthepressureremainsthesame.

CombiningVolumesSeeGay-Lussac’sunderlaws.ConservationofEnergyEnergycanbeneithercreatednordestroyed,sothattheenergyoftheuniverseisconstant.

ConservationofMatterMattercanbeneithercreatednordestroyed(orweightremainsconstantinanordinarychemicalchange).

Dalton’sWhenagasismadeupofamixtureofdifferentgases,thepressureofthemixtureisequaltothesumofthepartialpressuresofthecomponents.

DefiniteCompositionAcompoundiscomposedoftwoormoreelementschemicallycombinedinadefiniteratiobyweight.

Faraday’sDuringelectrolysis,theweightofanyelementliberatedisproportional(1)tothequantityofelectricitypassingthroughthecell,and(2)totheequivalentweightoftheelement.

FirstLawofThermodynamicsThetotalenergyoftheuniverseisconstantand

cannotbecreatedordestroyed.Gay-Lussac’sTheratiobetweenthecombiningvolumesofgasesandtheproduct,ifgaseous,canbeexpressedinsmallwholenumbers.

Graham’sTherateofdiffusion(oreffusion)ofagasisinverselyproportionaltothesquarerootofitsmolecularmass.

Henry’sThesolubilityofagas(unlessthegasisverysoluble)isdirectlyproportionaltothepressureappliedtothegas.

Hess’sIfaseriesofreactionsareaddedtogether,theenthalpychangeforthetotalreactionisthesumoftheenthalpychangesfortheindividualsteps.

IdealGasAnygasthatobeysthegaslawsperfectly.Nosuchgasactuallyexists.

MultipleProportionsWhenanytwoelements,AandB,combinetoformmorethanonecompound,thedifferentmassesofBthatunitewithafixedmassofAbearasmallwhole-numberratiotoeachother.

PeriodicThechemicalpropertiesofelementsvaryperiodicallywiththeiratomicnumbers.

SecondLawofThermodynamicsHeatcannot,ofitself,passfromacoldbodytoahotbody.

LeChâtelier’sPrincipleIfastressisplacedonasysteminequilibrium,thesystemwillreactinthedirectionthatrelievesthestress.

leptonAnelementaryparticle;theelectronandneutrinoarebelievedtoconsistofleptons.

LewisdotsymbolThechemicalsymbol(kernel)foranatom,surroundedbydotstorepresentitsouterlevelelectrons.Examples:K·,Sr:.

liquidAphaseofmatterthathasadefinitevolumebuttakestheshapeofthecontainer.

liquidairAirthathasbeencooledandcompresseduntilitliquefies.litmusAnorganicsubstance,obtainedfromthelichenplantandusedasanindicator;itturnsredinacidicsolutionandblueinbasicsolution.

LondonforceTheweakestofthevanderWaalsforcesbetweenmolecules.Theseweak,attractiveforcesbecomeapparentonlywhenthemoleculesapproachoneanotherclosely(usuallyatlowtemperaturesandhighpressure).

Theyareduetothewaythepositivechargesofonemoleculeattractthenegativechargesofanothermoleculebecauseofthechargedistributionatanyoneinstant.

luminousEmittingasteady,suffusedlight.

malleableCapableofbeinghammeredorpoundedintothinsheets.manometerAU-tube(containingmercuryorsomeotherliquid)usedtomeasurethepressureofaconfinedgas.

massThequantityofmatterthatasubstancepossesses;itcanbemeasuredbyitsresistancetoachangeinpositionormotion,andisnotrelatedtotheforceofgravity.

massnumberThenearestwholenumbertothecombinedatomicmassoftheindividualatomsofanisotopewhenthatmassisexpressedinatomicmassunits.

massspectographAdevicefordeterminingthemassesofelectricallychargedparticlesbyseparatingthemintodistinctstreamsbymeansofmagneticdeflection.

matterAsubstancethatoccupiesspace,hasmass,andcannotbecreatedordestroyedeasily.

meltingThechangeinphaseofasubstancefromsolidtoliquid.meltingpointThespecifictemperatureatwhichagivensolidchangestoaliquid.

mesonAnyunstable,elementarynuclearparticlehavingamassbetweenthatofanelectronandthatofaproton.

metal(a)Anelementwhoseoxidecombineswithwatertoformabase;(b)anelementthatreadilyloseselectronsandacquiresapositivevalence.

metallurgyTheprocessinvolvedinobtainingametalfromitsores.meterThebasicunitoflengthinthemetricsystem;definedas1,650,763.73timesthewavelengthofkrypton-86whenexcitedtogiveoffanorange-redspectralline.

MeVAunitforexpressingthekineticenergyofsubatomicparticles;equals106electronvolts.

micronOnethousandthofamillimeter(abbreviation:μ).mineralAninorganicsubstanceofdefinitecompositionfoundinnature.miscibleReferringtotheabilityoftwoliquidstomixwithoneanother.mixtureAsubstancecomposedoftwoormorecomponents,eachofwhichretainsitsownproperties.

moderatorAsubstancesuchasgraphite,paraffin,orheavywaterusedinanuclearreactortoslowdownneutrons.

molalsolutionAsolutioncontaining1moleofsolutein1,000gramsofsolvent(indicatedbym).

molarmassThemassarrivedatbytheadditionoftheatomicmassesoftheunitsthatmakeupamoleculeofanelementorcompound.Expressedingrams/mole,themolarmassofagaseoussubstanceatSTPoccupiesamolarvolumeequalto22.4liters.

molarsolutionAsolutioncontaining1moleofsolutein1,000millilitersofsolution(indicatedbyM).

moleAunitofquantitythatconsistsof6.02×1023particles.molecularmassThesumofthemassesofalltheatomsinamoleculeofasubstance.

moleculartheorySeeKinetic-MolecularTheory.moleculeThesmallestparticleofasubstancethatretainsthephysicalandchemicalpropertiesofthatsubstance.Example:He,Br2,H2O

monobasicacidAnacidhavingonlyonehydrogenatomthatcanbereplacedbyametalorapositiveradical.

mordantAchemical,suchasaluminumsulfate,usedforfixingcolorsontextiles.

multipleproportionsSeeunderlaws.

nascent(atomic)Referringtoanelementintheatomicformasithasjustbeenliberatedinachemicalreaction.

neutralizationTheunionofthehydrogenionofanacidandthehydroxylionofabasetoformwater.

neutronAsubatomicparticlefoundinthenucleusoftheatom;ithasnochargeandhasthesamemassastheproton.

neutroncaptureAnuclearreactioninwhichaneutronattachesitselftoanucleus;agammarayisusuallyemittedsimultaneously.

nitridingAprocessinwhichammoniaoracyanideisusedtoproducecase-hardenedsteel;anitrideisformedinsteadofacarbide.

nitrogenfixationAnyprocessbywhichatmosphericnitrogenisconvertedintoacompoundsuchasammoniaornitricacid.

noblegasAgaseouselementthathasacompleteouterlevelofelectrons;anyofagroupofraregases(helium,neon,argon,krypton,xenon,andradon)thatexhibitgreatstabilityandverylowreactionrates.

noblegasstructureTheouterenergylevelelectronconfigurationcharacteristicoftheinertgases—twoelectronsforhelium;eightelectronsforallothers.

nonelectrolyteAsubstancewhosesolutiondoesnotconductacurrentofelectricity.

nonmetal(a)Anelementwhoseoxidereactswithwatertoformanacid;(b)anelementthattakesonelectronsandacquiresanegativevalence.

nonpolarcompoundAcompoundinwhosemoleculestheatomsarearrangedsymmetricallysothattheelectricchargesareuniformlydistributed.

normalsaltAsaltinwhichallthehydrogenoftheacidhasbeendisplacedbyametal.

normalsolutionAsolutionthatcontains1gramofH+(oritsequivalent:17gofOH−,23gofNa+,20gofCa2+,etc.)in1literofsolution(indicatedbyN).

nuclearenergyTheenergyreleasedbyspontaneouslyorartificiallyproducedfission,fusion,ordisintegrationofthenucleiofatoms.

nuclearfuelAsubstancethatisconsumedduringnuclearfissionorfusion.nuclearreactionAnyreactioninvolvingachangeinnuclearstructure.nuclearreactorAdeviceinwhichacontrolledchainreactionoffissionablematerialcanbeproduced.

nucleonicsThesciencethatdealswiththeconstituentsandallthechangesintheatomicnucleus.

nucleusThecenteroftheatom,whichcontainsprotonsandneutrons.

nuclideAspeciesofatomcharacterizedbytheconstitutionofitsnucleus.

orbitalAsubdivisionofanuclearshell;itmaycontainnone,one,ortwoelectrons.

oreAnaturalmineralsubstancefromwhichanelement,usuallyametal,maybeobtainedwithprofit.

organicacidAnorganiccompoundthatcontainsthe–COOHgroup.organicchemistryThebranchofchemistrydealingwithcarboncompounds,usuallythosefoundinnature.

oxidationThechemicalprocessbywhichoxygenisattachedtoasubstance;theprocessoflosingelectrons.

oxidationnumber(state)Apositiveornegativenumberrepresentingthechargethatanionhasoranatomappearstohavewhenitselectronsarecountedaccordingtoarbitrarilyacceptedrules:(1)electronssharedbytwounlikeatomsarecountedwiththemoreelectronegativeatom;(2)electronssharedbytwolikeatomsaredividedequallybetweentheatoms.

oxidationpotentialAnelectrodepotentialassociatedwiththeoxidationhalf-reaction.

oxidizingagentAsubstancethat(a)givesupitsoxygenreadily,(b)removeshydrogenfromacompound,(c)takeselectronsfromanelement.

ozoneAnallotropicandveryactiveformofoxygen,havingtheformulaO3.

paraffinseriesThemethaneseriesofhydrocarbons.pascalTheSIunitofpressure,equalto1newtonpersquaremeter.pasteurizationPartialsterilizationofasubstance,suchasmilk,byheatingtoapproximately65°Cfor½hour.

PauliExclusionPrincipleEachelectronorbitalofanatomcanbefilledbyonlytwoelectrons,whichhaveoppositespins.

periodAhorizontalrowofelementsinthePeriodicTable.PeriodicLawSeeunderlaws.petroleum(meaning“oilfromstone”)Acomplexmixtureofgaseous,liquid,

andsolidhydrocarbonsobtainedfromtheearth.pHAnumericalexpressionofthehydrogenorhydroniumionconcentrationinasolution;definedas–log[H+],where[H+]istheconcentrationofhydrogenions,inmolesperliter.

phenolphthaleinAnorganicindicator;itiscolorlessinacidsolutionandredinthepresenceofOH−ions.

photosynthesisThereactiontakingplaceinallgreenplantsthatproducesglucosefromcarbondioxideandwaterunderthecatalyticactionofchlorophyllinthepresenceoflight.

physicalchangeAchangethatdoesnotinvolveanyalterationinchemicalcomposition.

physicalpropertyApropertyofasubstancearrivedatthroughobservationofitssmell,taste,color,density,andsoon,whichdoesnotrelatetochemicalactivity.

pibondAbondbetweenporbitals.pileAgeneraltermforanuclearreactor;specifically,agraphite-moderatedreactorinwhichuraniumfuelisdistributedthroughouta“pile”ofgraphiteblocks.

pitchblendeAmassivevarietyofuraninitethatcontainsasmallamountofradium.

plasmaVeryhotionizedgases.polarcovalentbondAbondinwhichelectronsareclosertooneatomthantoanother.Seealsopolarmolecule.

polardotstructureRepresentationofthearrangementsofelectronsaroundtheatomsofamoleculeinwhichthepolarcharacteristicsareshownbyplacingtheelectronsclosertothemoreelectronegativeatom.

polarmoleculeAmoleculethathasdifferentlychargedareasbecauseofunequalsharingofelectrons.

polyatomicionAgroupofchemicallyunitedatomsthatreactasaunitandhaveanelectriccharge.

polymerizationTheprocessofcombiningseveralmoleculestoformonelargemolecule(polymer).

(a)Additionalpolymerization:Theadditionofunsaturatedmoleculestoeachother.(b)Condensationpolymerization:Thereactionoftwomoleculesbylossofamoleculeofwater.

positronApositivelychargedparticleofelectricitywithaboutthesameweightastheelectron.

potentialenergyEnergyduetothepositionofabodyortotheconfigurationofitsparticles.

precipitateAninsolublecompoundformedinthechemicalreactionbetweentwoormoresubstancesinsolution.

proteinsLarge,complexorganicmolecules,withnitrogenanessentialpart,foundinplantsandanimals.

protonAsubatomicparticlefoundinthenucleusthathasapositivecharge.

qualitativeanalysisAtermappliedtothemethodsandproceduresusedtodetermineanyoralloftheconstituentpartsofasubstance.

quantitativeanalysisAtermappliedtothemethodsandproceduresusedtodeterminethedefinitequantityorpercentageofanyoralloftheconstituentpartsofasubstance.

quenchingCoolingahotpieceofmetalrapidly,asinwateroroil.radiationTheemissionofparticlesandraysfromaradioactivesource;usuallyalphaandbetaparticlesandgammarays.

radioactiveReferringtosubstancesthathavetheabilitytoemitradiations(alphaorbetaparticlesorgammarays).

radioisotopeAnisotopesthatisradioactive,suchasuranium-235.reactantAsubstanceinvolvedinareaction.reactionAchemicaltransformationorchange.Thefourbasictypesarecombination(synthesis),decomposition(analysis),singlereplacementorsingledisplacement,anddoublereplacementordoubledisplacement.

reactionpotentialThesumoftheoxidationpotentialandreductionpotentialforaparticularreaction.

reagentAnychemicaltakingpartinareaction.

recrystallizationAseriesofcrystallizations,repeatedforthepurposeofgreaterpurification.

redoxAshortenednameforareactionthatinvolvesreductionandoxidation.reducingagentFromanelectronstandpoint,asubstancethatlosesitsvalenceelectronstoanotherelement;asubstancethatisreadilyoxidized.

reductionAchemicalreactionthatremovesoxygenfromasubstance;againofelectrons.

reductionpotentialAnelectrodepotentialassociatedwithareductionhalf-reaction.

refraction(oflight)Thebendingoflightraysastheypassfromonematerialintoanother.

relativehumidityTheratio,expressedinpercent,betweentheamountofwatervaporinagivenvolumeofairandtheamountthesamevolumecanholdwhensaturatedatthesametemperature.

resonanceThephenomenoninamolecularstructurethatexhibitspropertiesbetweenthoseofasinglebondandthoseofadoublebondandthuspossessestwoormorealternativestructures.

reversiblereactionAnyreactionthatreachesanequilibrium,orthatcanbemadetoproceedfromrighttoleftaswellasfromlefttoright.

roastingHeatinganore(usuallyasulfide)inanexcessofairtoconverttheoretoanoxide,whichcanthenbereduced.

saltAcompound,suchasNaCl,madeupofapositivemetallicionandanegativenonmetallicionorradical.

saturatedsolutionAsolutionthatcontainsthemaximumamountofsoluteundertheexistingtemperatureandpressure.

SecondLawofThermodynamicsSeeunderlaws.sigmabondAbondbetweensorbitalsorbetweenansorbitalandanotherkindoforbital.

significantfiguresAllthecertaindigits,thatis,thoserecordedinameasurement,plusoneuncertaindigit.

slagTheproductformedwhenthefluxreactswiththeimpuritiesofanoreina

metallurgicalprocess.solidAphaseofmatterthathasadefinitesizeandshape.solubilityAmeasureoftheamountofsolutethatwilldissolveinagivenquantityofsolventatagiventemperature.

soluteThematerialthatisdissolvedtomakeasolution.solutionAuniformmixtureofasoluteinasolvent.solventThedispersingsubstancethatallowsthesolutetogointosolution.specificgravity(mass)Theratiobetweenthemassofacertainvolumeofasubstanceandthemassofanequalvolumeofwater(or,inthecaseofgases,anequalvolumeofair);expressedasasinglenumber.

specificheatTheratiobetweenthenumberofcaloriesneededtoraisethetemperatureofacertainmassofasubstance1degreeontheCelsiusscaleandthenumberofcaloriesneededtoraisethetemperatureofthesamemassofwater1degreeontheCelsiusscale.

spectroscopeAninstrumentusedtoanalyzelightbyseparatingitintoitscomponentwavelengths.

spectrumTheimageformedwhenradiantenergyisdispersedbyaprismorgratingintoitsvariouswavelengths.

spinthariscopeAdeviceforviewingthroughamicroscopetheflashesoflightmadebyparticlesfromradioactivematerialsagainstasensitizedscreen.

spontaneouscombustion(ignition)Theprocessinwhichslowoxidationproducesenoughheattoraisethetemperatureofasubstancetoitskindlingtemperature.

stableReferringtoasubstancenoteasilydecomposedordissociated.standardconditionsAnatmosphericpressureof760millimetersortorror1atmosphere(mercurypressure)andatemperatureof0°C(273K)(abbreviation:STP).

stratosphereTheupperportionoftheatmosphere,inwhichthetemperaturechangesbutlittlewithaltitude,andcloudsofwaterneverform.

strongacid(orbase)Anacid(orabase)capableofahighdegreeofionizationinwatersolution.Example:sulfuricacid(sodiumhydroxide).

structural(graphic)formulaApictorialrepresentationoftheatomicarrangementofamolecule.

sublimeTovaporizedirectlyfromthesolidtothegaseousstate,andthencondensebacktothesolid.

substanceAsinglekindofmatter,element,orcompound.substitutionproductAproductformedbythesubstitutionofotherelementsorradicalsforhydrogenatomsinhydrocarbons.

sulfationAnaccumulationofleadsulfateontheplatesandatthebottomofa(lead)storagecell.

supersaturatedsolutionAsolutionthatcontainsagreaterquantityofsolutethanisnormallypossibleatagiventemperature.

suspensionAmixtureoffinelydividedsolidmaterialinaliquid,fromwhichthesolidsettlesonstanding.

symbolAletterorlettersrepresentinganelementoftheperiodictable.Examples:O,Mn.

synthesisThechemicalprocessofformingasubstancefromitsindividualparts.SystèmeInternationald’UnitésThemodernizedmetricsystemofmeasurementsuniversallyusedbyscientists.Therearesevenbaseunits:kilogram,meter,second,ampere,kelvin,mole,andcandela.

temperatureTheintensityorthedegreeofheatofabody,measuredbyathermometer.

temperingTheheatingandthenrapidcoolingofametaltoincreaseitshardness.

ternaryReferringtoacompoundcomposedofthreedifferentelements,suchasH2SO4.

theoryAnexplanationusedtointerpretthe“mechanics”ofnature’sactions;atheoryismorefullydevelopedthanahypothesis.

thermochemicalequationAnequationthatincludesvaluesforthecaloriesabsorbedorevolved.

thermoplasticCapableofbeingsoftenedbyheat;mayberemolded.

thermosettingCapableofbeingpermanentlyhardenedbyheatandpressure;resistanttothefurthereffectsofheat.

tinctureAnalcoholicsolutionofasubstance,suchasatinctureofiodine.torrAunitofpressuredefinedas1millimeterofmercury;1torrequals133.32pascals.

tracerAminutequantityofradioactiveisotopeusedinmedicineandbiologytostudychemicalchangeswithinlivingtissues.

transmutationConversionofoneelementintoanother,eitherbybombardmentorbyradioactivedisintegration.

tribasicacidAnacidthatcontainsthreereplaceablehydrogenatomsinitsmolecule,suchasH3PO4.

tritiumAveryrare,unstable,“triple-weight”hydrogenisotope(H3)thatcanbemadesynthetically.

TyndalleffectThescatteringofabeamoflightasitpassesthroughacolloidalmaterial.

ultravioletlightTheportionofthespectrumthatliesjustbeyondtheviolet;thereforeofshortwavelength.

U.S.P.(UnitedStatesPharmacopeia)chemicalsChemicalscertifiedashavingastandardofpuritythatdemonstratestheirfitnessforuseinmedicine.

valenceThecombiningpowerofanelement;thenumberofelectronsgained,lost,orborrowedinachemicalreaction.

valenceelectronsTheelectronsintheoutermostlevelorlevelsofanatomthatdetermineitschemicalproperties.

vanderWaalsforcesWeakattractiveforcesexistingbetweenmolecules.vaporThegaseousphaseofasubstancethatnormallyexistsasasolidorliquidatordinarytemperatures.

vaporpressureThepressureexertedbyavaporgivenoffbyaconfinedliquidorsolidwhenthevaporisinequilibriumwithitsliquidorsolidform.

volatileEasilychangedtoagasoravaporatrelativelylowpressure.

voltAunitofelectricalpotentialorvoltage,equaltothedifferenceofpotentialbetweentwopointsinaconductingwirecarryingaconstantcurrentof1amperewhenthepowerdissipatedbetweenthesetwopointsisequalto1watt(abbreviation:V).

volumeTheamountofthree-dimensionalspaceoccupiedbyasubstance.VSEPRThevalenceshellelectronpairrepulsionmodel.Itexpressesthenon-90°variationsinbondanglesforporbitalsintheouterenergylevelsofatomsinmoleculesbecauseofelectronrepulsions.

waterofhydrationWaterthatisheldinchemicalcombinationinahydrateandcanberemovedwithoutessentiallyalteringthecompositionofthesubstance.SeealsoHydrate.

weakacid(orbase)Anacid(orbase)capableofbeingonlyslightlyionizedinanaqueoussolution.Example:aceticacid(ammoniumhydroxide).

weakelectrolyteAsubstancethat,whendissolvedinwater,ionizesonlyslightlyandhenceisapoorconductorofelectricity.

weightThemeasureoftheforcewithwhichabodyisattractedtowardEarthbygravity.

workTheproductoftheforceexertedonabodyandthedistancethroughwhichtheforceacts;expressedmathematicallybytheequationW=Fs,whereW=work,F=force,ands=distance.

X-raysPenetratingradiations,ofextremelyshortwavelength,emittedwhenastreamofelectronsstrikesasolidtargetinavacuumtube.

zeoliteAnaturalorsynthesizedsilicateusedtosoftenwater.