chemistry sl paper 2 tz1 2009 - exam(iii) explain why the following reaction can also be described...

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SECTION A

Answer all the questions in the spaces provided.

1. Biodiesel makes use of plants’ ability to fix atmospheric carbon by photosynthesis.Many companies and individuals are now using biodiesel as a fuel in order to reducetheir carbon footprint. Biodiesel can be synthesized from vegetable oil according to thefollowingreaction.

vegetableoil methanol glycerol biodiesel

(a) Identifytheorganicfunctionalgrouppresentinbothvegetableoilandbiodiesel.

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[1]

(b) For part of her extended essay investigation into the efficiency of the process,a student reacted a pure sample of a vegetable oil (whereR=C17H33)withmethanol.Therawdatarecordedforthereactionisbelow.

Massofoil =1013.0g Massofmethanol = 200.0g Massofsodiumhydroxide = 3.5g Massofbiodieselproduced= 811.0g

Therelativemolecularmassoftheoilusedbythestudentis885.6.Calculatetheamount(inmoles)oftheoilandthemethanolused,andhencetheamount(inmoles)ofexcessmethanol.

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[3]

(This question continues on the following page)

3CH3OH(l)(l)+ (l)+3

H C

C

H

O

H

CH

H

O

O COC

R

OC R

R

O

CH3 O C RO

H C

H

OH

CH OH

CH OH

H

NaOH(s)(l)

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(Question 1 continued)

(c) The reversible arrows in the equation indicate that the production of biodiesel is anequilibriumprocess.

(i) Statewhatismeantbythetermdynamic equilibrium.

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[1]

(ii) Using the abbreviations [vegetable oil], [methanol], [glycerol] and [biodiesel]deducetheequilibriumconstantexpression(Kc)forthisreaction.

[1]

(iii) Suggestareasonwhyexcessmethanolisusedinthisprocess.

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[1]

(iv) Stateandexplaintheeffectthattheadditionofthesodiumhydroxidecatalystwillhaveonthepositionofequilibrium.

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[2]

(d) Thereactantshadtobestirredvigorouslybecausetheyformedtwodistinctlayersinthereactionvessel.Explainwhytheyformtwodistinctlayersandwhystirringincreasestherateofreaction.

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[2]


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(e) Calculatethepercentageyieldofbiodieselobtainedinthisprocess.

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[2]

(f) Whenbiodieseliscombusteditproducescarbondioxide.Explainwhytheuseofbiodieselasafueldoesnotsignificantlycontributetoglobalwarming.

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[1]

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2. TwostudentswereaskedtouseinformationfromtheDataBooklettocalculateavaluefortheenthalpyofhydrogenationofethenetoformethane.

C H (g) H (g) C H (g)2 4 2 2 6

JohnusedtheaveragebondenthalpiesfromTable10.MaritusedthevaluesofenthalpiesofcombustionfromTable12.

(a) CalculatethevaluefortheenthalpyofhydrogenationofetheneobtainedusingtheaveragebondenthalpiesgiveninTable10.

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[2]

(b) MaritarrangedthevaluesshefoundinTable12intoanenergycycle.

C2H4(g) + H2(g) C2H6(g)

3O2

2CO2(g) + 3H2O

–1411kJmol–1

–286

kJmol–1

–1560 k

J mol–1

(hydrogenation)

(l)

Calculatethevaluefortheenthalpyofhydrogenationofethenefromtheenergycycle.

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[1]

(c) SuggestonereasonwhyJohn’sanswerisslightlylessaccuratethanMarit’sanswer.

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[1]


ë ÖH

1 22O

31 22O

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(d) Johnthendecidedtodeterminetheenthalpyofhydrogenationofcyclohexenetoproducecyclohexane.

C H l H g C H l6 10 2 6 12( ) ( ) ( )

(i) Usetheaveragebondenthalpiestodeduceavaluefortheenthalpyofhydrogenationofcyclohexene.

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[1]

(ii) Thepercentagedifferencebetween these twomethods (averagebond enthalpiesandenthalpiesofcombustion) isgreater forcyclohexene than itwas forethene.John’shypothesiswasthatitwouldbethesame.Determinewhytheuseofaveragebond enthalpies is less accurate for the cyclohexene equation shown above,thanitwasforethene.Deducewhatextrainformationisneededtoprovideamoreaccurateanswer.

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[2]

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3. Sodiumoxide,Na2O,isawhitesolidwithahighmeltingpoint.

(a) Explainwhysolidsodiumoxideisanon-conductorofelectricity.

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[1]

(b) Molten sodium oxide is a good conductor of electricity. State the half-equation forthe reaction occurring at the positive electrode during the electrolysis of moltensodiumoxide.

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[1]

(c) (i) Statetheacid-basenatureofsodiumoxide.

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[1]

(ii) Statetheequationforthereactionofsodiumoxidewithwater.

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[1]

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4. (a) Defineoxidationintermsofelectrontransfer.

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[1]

(b) Chlorine can be made by reacting concentrated hydrochloric acid with potassiummanganate(VII),KMnO4.

2KMnO (aq) 16HCl(aq) 2MnCl (aq) 2KCl(aq) 5Cl (aq) 8H O(aq)4 2 2 2

(i) StatetheoxidationnumberofmanganeseinKMnO4andinMnCl2.

KMnO4 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

MnCl2 ........................................................

[2]

(ii) Deducewhichspecieshasbeenoxidizedin thisreactionandstate thechangeinoxidationnumberthatithasundergone.

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[2]

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SECTION B

Answer one question. Write your answers on the answer sheets provided. Write your session number on each answer sheet, and attach them to this examination paper and your cover sheet using the tag provided.

5. (a) (i) Describeandexplaintheoperationofamassspectrometer. [5]

(ii) State three factors that affect the degree of deflection of ions in amassspectrometer. [3]

(iii) Strontiumexistsasfournaturally-occurringisotopes.Calculatetherelativeatomicmassofstrontiumtotwodecimalplacesfromthefollowingdata.

Isotope Percentage abundanceSr-84 0.56Sr-86 9.90Sr-87 7.00Sr-88 82.54

[2]


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(b) Thegraphofthefirstionizationenergyplottedagainstatomicnumberforthefirsttwentyelementsshowsperiodicity.

Firstionizationenergy/kJmol–1

2500

2000

1500

1000

500

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20

Atomicnumber

(i) Define the term first ionization energy and state what is meant by thetermperiodicity. [2]

(ii) State the electron arrangement of argon and explain why the noble gases,helium, neon and argon show the highest first ionization energies for theirrespectiveperiods. [3]

(iii) A graph of atomic radius plotted against atomic number shows that the atomicradiusdecreasesacrossaperiod.Explainwhychlorinehasasmalleratomicradiusthansodium. [1]

(iv) Explainwhyasulfideion,S2–,islargerthanachlorideion,Cl–. [1]

(v) ExplainwhythemeltingpointsoftheGroup1metals ( )Li Cs decreasedownthegroupwhereas themeltingpointsof theGroup7elements ( )F I increasedownthegroup. [3]

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6. (a) (i) Draw the Lewis structures for carbonmonoxide, CO, carbon dioxide, CO2 andmethanol,CH3OH. [3]

(ii) List,with an explanation, the three compounds inorderof increasing carbon tooxygenbondlength(shortestfirst). [2]

(b) Predicttheshapeandbondanglesforthefollowingspecies:

(i) CO2

(ii) CO32–

(iii) BF4–

[2]

[2]

[2]

(c) (i) DefineaBrønsted-Lowryacid. [1]

(ii) Deducethetwoacidsandtheirconjugatebasesinthefollowingreaction:

H O (l) NH (aq) OH (aq) NH (aq)2 3 4U [2]

(iii) Explainwhythefollowingreactioncanalsobedescribedasanacid-basereaction.

F (g) BF (g) BF (s)3 4U [2]

(d) Ethanoicacid,CH3COOH,isaweakacid.

(i) Definethetermweak acidandstatetheequationforthereactionofethanoicacidwithwater. [2]

(ii) Vinegar,whichcontainsethanoicacid,canbeused tocleandepositsofcalciumcarbonatefromtheelementsofelectrickettles.Statetheequationforthereactionofethanoicacidwithcalciumcarbonate. [2]

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7. (a) Three compounds with similar relative molecular masses are butane, propanal andpropan-1-ol.

(i) List the three compounds in order of increasing boiling point (lowest first) andexplainthedifferencesintheirboilingpoints. [4]

(ii) Predict, with an explanation, which of the three compounds is least soluble ormiscibleinwater. [2]

(iii) When propan-1-ol is oxidized using a warm acidified solution of potassiumdichromate(VI)twodifferentorganicproductscanbeobtained.Deducethenameandstructuralformulaforeachofthesetwoproducts. [3]

(iv) Propan-2-olisanisomerofpropan-1-ol.Drawthestructureofpropan-2-ol. [1]

(v) Identifytheclassofalcoholsthatpropan-2-olbelongstoandstatethenameoftheorganicproductformedwhenitisoxidizedbyanacidifiedsolutionofpotassiumdichromate(VI). [2]

(b) Ethanolcanbeformedfrometheneinatwostepreaction:

H

C

H

C

H

H

H C

H

H

C

Br

H

H H C

H

C

H

OH

H

H(g) (g) (l)step 1 step 2

(i) Statethenameofthereagentusedforstep1. [1]

(ii) Statethenameofthereagentandtheconditionsusedforstep2. [2]

(iii) Themechanisminvolvedinstep2isSN2.Explainhowthereactionproceedsusingcurlyarrowstorepresentthemovementofelectronpairs. [3]

(iv) Outlinehowethanolismanufacturedfrometheneinindustryandstateoneimportantcommercialuseofethanol. [2]

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SECTION A


1. Brassisacoppercontainingalloywithmanyuses.Ananalysisiscarriedouttodeterminethepercentageofcopperpresentinthreeidenticalsamplesofbrass.Thereactionsinvolvedinthisanalysisareshownbelow.

Step1:Cu (s) 2HNO (aq) 2H (aq) Cu (aq) 2NO (g) 2H O(l)3+ 2+

2 2

Step2:4I (aq) 2Cu (aq) 2CuI (s) I (aq)2+2

Step3:I (aq) 2S O (aq) 2I (aq) S O (aq)2 2 32

4 62

(a) (i) Deducethechangeintheoxidationnumbersofcopperandnitrogeninstep1.

Copper:

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[2]

(ii) Identifytheoxidizingagentinstep1.

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[1]

(b) Astudentcarriedoutthisexperimentthreetimes,withthreeidenticalsmallbrassnails,andobtainedthefollowingresults.

Massofbrass =0.456g 0.001 g

Titre 1 2 3

Initial volume of 0.100 mol dm–3 S2O32– ( 0.05 cm )3 0.00 0.00 0.00

Final volume of 0.100 mol dm–3 S2O32– ( 0.05 cm )3 28.50 28.60 28.40

Volume added of 0.100 mol dm–3 S2O32– ( 0.10 cm )3 28.50 28.60 28.40

Average volume added of 0.100 mol dm–3 S2O32– ( 0.10 cm )3 28.50


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(i) Calculatetheaverageamount,inmol,ofS2O32–addedinstep3.

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[2]

(ii) Calculatetheamount,inmol,ofcopperpresentinthebrass.

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[1]

(iii) Calculatethemassofcopperinthebrass.

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[1]

(iv) Calculatethepercentagebymassofcopperinthebrass.

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[1]

(v) Themanufacturersclaimthatthesampleofbrasscontains44.2%copperbymass.Determinethepercentageerrorintheresult.

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[1]

(c) Withreferencetoitsmetallicstructure,describehowbrassconductselectricity.

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[1]

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2. AlexandHannahwereaskedtoinvestigatethekineticsinvolvedintheiodinationofpropanone.Theyweregiventhefollowingequationbytheirteacher.

+H (aq)

3 3 2 2 3CH COCH (aq) I (aq) CH ICOCH (aq) HI (aq)

Alex’s hypothesiswas that the ratewill be affected by changing the concentrations of thepropanoneandtheiodine,asthereactioncanhappenwithoutacatalyst.Hannah’shypothesiswas that as the catalyst is involved in the reaction, the concentrations of the propanone,iodineandthehydrogenionswillallaffecttherate.

Theycarriedoutseveralexperimentsvaryingtheconcentrationofoneofthereactantsorthecatalystwhilstkeepingotherconcentrationsandconditionsthesame.Theirresultsareshowngraphicallybelow.

Rate

Rate

Rate

[H+(aq)] [CH3COCH3(aq)] [I2(aq)]

(a) DiscusswhethereitherAlex’sorHannah’shypothesisiscorrect.

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[2]

(b) Explainwhythereactionratewillincreasewithincreasingtemperature.

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[2]


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(c) (i) Thisreactionusesacatalyst.SketchandannotatetheMaxwell-Boltzmannenergydistributioncurveforareactionwithandwithoutacatalystonlabelledaxesbelow. [3]

(ii) Describehowacatalystworks.

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[1]

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3. (a) Chloroethene,C2H3Cl,isanimportantorganiccompoundusedtomanufacturethepolymerpoly(chloroethene).

(i) DrawtheLewisstructureforchloroetheneandpredicttheH–C–Clbondangle.

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[2]

(ii) Drawasectionofpoly(chloroethene)containingsixcarbonatoms. [1]

(iii) Outlinewhythepolymerizationofalkenesisofeconomicimportanceandwhythedisposalofplasticsisaproblem.

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[2]

(b) (i) Chloroethenecanbeconvertedtoethanolintwosteps.Foreachstepdeduceanoverallequationforthereactiontakingplace.

Step1:

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Step2:

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[2]


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(ii) Statethereagentsandconditionsnecessarytoprepareethanoicacidfromethanolinthelaboratory.

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[2]

(iii) Stateanequation,includingstatesymbols,forthereactionofethanoicacidwithwater.IdentifyaBrønsted-Lowryacidintheequationanditsconjugatebase.

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[3]

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SECTION B


4. (a) Definethetermrelative atomic mass(Ar). [1]

(b) Relativeatomicmassesareobtainedusingamassspectrometer.Drawasimpleannotateddiagramofthemassspectrometer. [5]

(c) Therelativeatomicmassofnaturallyoccurringcopperis63.55.Calculatetheabundancesof63Cuand65Cuinnaturallyoccurringcopper. [2]

(d) Theisotopesofsomeelementsareradioactive.Statearadioisotopeusedinmedicine. [1]

(e) Stateabalancedequationforthereactionofsodiumwithwater.Includestatesymbols. [2]

(f) Withreferencetoelectronicarrangements,suggestwhythereactionbetweenrubidiumandwaterismorevigorousthanthatbetweensodiumandwater. [2]

(g) Describeandexplainwhatyouwillseeifchlorinegasisbubbledthroughasolutionof

(i) potassiumiodide.

(ii) potassiumfluoride.

[2]

[1]

(h) Explainwhythemeltingpointsoftheelementsdecreasedowngroup1andincreasedowngroup7. [4]

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5. (a) (i) Drawanannotateddiagramofavoltaiccellcomposedofamagnesiumelectrodein1.0moldm–3magnesiumnitratesolutionandasilverelectrodein1.0moldm–3silvernitratesolution.Statethedirectionofelectronflowonyourdiagram. [4]

(ii) Deducehalf-equationsfortheoxidationandreductionreactions. [2]

(b) Considerthefollowingthreeredoxreactions.

Cd (s) Ni (aq) Cd (aq) Ni (s)2+ 2+

Ni (s) 2Ag (aq) Ni (aq) 2Ag (s)+ 2+

Zn (s) Cd (aq) Zn (aq) Cd (s)2+ 2+

(i) Deducetheorderofreactivityofthefourmetals,cadmium,nickel,silverandzincandlistinorderofdecreasingreactivity. [2]

(ii) Identifythebestoxidizingagentandthebestreducingagent. [2]

(c) (i) Solidsodiumchloridedoesnotconductelectricitybutmoltensodiumchloridedoes.Explainthisdifference. [2]

(ii) Outlinewhathappensinanelectrolyticcellduringtheelectrolysisofmoltensodiumchlorideusing inert electrodes. Deduceequations for the reactionsoccurringateachelectrode. [4]

(d) (i) Astateofequilibriumcanexistwhenapieceofcoppermetalisplacedinasolutionofcopper(II)sulfate.Outlinethecharacteristicsofachemicalsystemindynamicequilibrium. [2]

(ii) ForanexothermicreactionstatehowanincreaseintemperaturewouldaffectbothKcandthepositionofequilibrium. [2]

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6. (a) Inanexperimenttomeasuretheenthalpychangeofcombustionofethanol,astudentheatedacoppercalorimetercontaining100cm3ofwaterwithaspiritlampandcollectedthefollowingdata.

Initialtemperatureofwater: 20.0 DC Finaltemperatureofwater: 55.0 DC Massofethanolburned: 1.78g Densityofwater: 1.00gcm–3

(i) Usethedatatocalculatetheheatevolvedwhentheethanolwascombusted. [2]

(ii) Calculatetheenthalpychangeofcombustionpermoleofethanol. [2]

(iii) Suggest two reasons why the result is not the same as the value in theDataBooklet. [2]

(b) Ethanol is part of the homologous series of alcohols. Describe two features of ahomologousseries. [2]


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(c) (i) Beloware four structural isomersof alcoholswithmolecular formulaC4H10O.StatethenameofeachoftheisomersA,B,CandD. [4]

Key:

Oxygen

Carbon

Hydrogen

A B

C D

(ii) Determinetheisomerthatcannotbeoxidizedbyacidifiedpotassiumdichromate(VI),K2Cr2O7. [1]

(iii) Determinetheisomerwhichcanbeoxidizedtobutanal. [1]

(iv) Determinetheisomerwhichcanbeoxidizedtobutanone. [1]

(v) SuggestthestructuralformulaofanotherisomerofC4H10O. [1]

(d) (i) IsomerA isformedbyreacting1-bromobutanewithaqueoussodiumhydroxide.StatewhetherthereactionwouldproceedviaanSN1orSN2mechanism. [1]

(ii) Explain themechanismnamedinpart(d)(i)usingcurlyarrowstorepresent themovementofelectronpairs. [3]

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SECTION A


1. Thepercentagebymassofcalciumcarbonate ineggshellwasdeterminedbyaddingexcesshydrochloricacidtoensurethatallthecalciumcarbonatehadreacted.Theexcessacidleftwasthentitratedwithaqueoussodiumhydroxide.

(a) Astudentadded27.20cm3of0.200moldm–3HClto0.188gofeggshell.Calculatetheamount,inmol,ofHCladded.

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[1]

(b) The excess acid requires 23.80cm3 of 0.100moldm–3 NaOH for neutralization.Calculatetheamount,inmol,ofacidthatisinexcess.

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[1]

(c) Determine the amount, in mol, of HCl that reacted with the calcium carbonate intheeggshell.

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[1]

(d) StatetheequationforthereactionofHClwiththecalciumcarbonateintheeggshell.

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[2]

(e) Determinetheamount,inmol,ofcalciumcarbonateinthesampleoftheeggshell.

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[2]


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(f) Calculate the mass and the percentage by mass of calcium carbonate in theeggshellsample.

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[3]

(g) Deduceoneassumptionmadeinarrivingatthepercentageofcalciumcarbonateintheeggshellsample.

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[1]

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2. Drawandlabelanenergyleveldiagramforthehydrogenatom.Inyourdiagramshowhowtheseriesoflinesintheultravioletandvisibleregionsofitsemissionspectrumareproduced,clearlylabellingeachseries. [4]

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3. Considerthebondingandstructureoftheperiod3elements.

(a) Explaintheincreaseinthemeltingpointfromsodiumtoaluminium.

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[2]

(b) Explainwhysulfur,S8,hasahighermeltingpointthanphosphorus,P4.

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[2]

(c) Explainwhysiliconhasthehighestmeltingpointandargonhasthelowestmeltingpoint.

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[2]

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4. One important property of a rocket fuel mixture is the large volume of gaseous productsformedwhichprovidethrust.Hydrazine,N2H4,isoftenusedasarocketfuel.Thecombustionofhydrazineisrepresentedbytheequationbelow.

N H g O g N g H O g kJmolc2 4 2 2 212 585( ) ( ) ( ) ( ) H Ö

(a) Hydrazine reacts with fluorine to produce nitrogen and hydrogen fluoride, all in thegaseousstate.Stateanequationforthereaction.

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[2]

(b) DrawtheLewisstructuresforhydrazineandnitrogen. [2]

(c) UsetheaveragebondenthalpiesgiveninTable10oftheDataBooklettodeterminetheenthalpychangeforthereactioninpart(a)above.

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[3]

(d) Basedonyouranswerstoparts(a)and(c),suggestwhetheramixtureofhydrazineandfluorineisabetterrocketfuelthanamixtureofhydrazineandoxygen.

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[2]

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SECTION B


5. Theperiodictableshowstherelationshipbetweenelectronarrangementandthepropertiesofelementsandisavaluabletoolformakingpredictionsinchemistry.

(a) (i) Identifythepropertyusedtoarrangetheelementsintheperiodictable. [1]

(ii) Outlinetworeasonswhyelectronegativityincreasesacrossperiod3intheperiodictableandonereasonwhynoblegasesarenotassignedelectronegativityvalues. [3]

(b) (i) Definethetermfirst ionization energyofanatom. [2]

(ii) Explainthegeneralincreasingtrendinthefirstionizationenergiesoftheperiod3elements,NatoAr. [2]

(iii) Explainwhysodiumconductselectricitybutphosphorusdoesnot. [2]

(c) The word redox comes from a combination of the terms reduction and oxidation.Redoxreactionsaffectourdailylives.

Theoverallreactionthattakesplaceinavoltaiccellisshownbelow.

Pb (s PbO (s 2H SO (aq PbSO (s H O(l2 2 4 4 2) ) ) ) )2 2

(i) DeterminetheoxidationnumberofleadinPb,PbO2andPbSO4. [1]

(ii) Deducetheoxidationandreductionhalf-equationstakingplaceatthenegativeleadelectrode(anode)andthepositivelead(IV)oxideelectrode(cathode).Deducetheoxidizingandreducingagentsandstatethedirectionoftheelectronflowbetweentheelectrodes. [4]

(iii) Inordertodeterminethepositionofthreemetalsinareactivityseries,themetalswere placed in different solutions of metal ions. The table below summarizeswhetherornotareactionoccurred.

Ag+(aq) Cu2+(aq) Pb2+(aq)Ag (s) Noreaction NoreactionCu (s) Reaction NoreactionPb (s) Reaction Reaction

Statetheequationsforthethreereactionsthattakeplace.UsethisinformationtoplacethemetalsAg,CuandPbinareactivityseries,withthestrongestreducingagentfirst,andexplainyourreasoning. [5]

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6. (a) WaterisanimportantsubstancethatisabundantontheEarth’ssurface.Waterdissociatesaccordingtothefollowingequation.

H O(l H aq OH aq2 ) ( ) ( )U

(i) Statetheequilibriumconstantexpressionforthedissociationofwater. [1]

(ii) ExplainwhyevenaveryacidicaqueoussolutionstillhassomeOH–ionspresentinit. [1]

(iii) Stateandexplaintheeffectofincreasingtemperatureontheequilibriumconstantabovegiventhatthedissociationofwaterisanendothermicprocess. [3]

(iv) ThepHofasolutionis2.IfitspHisincreasedto6,deducehowthehydrogenionconcentrationchanges. [2]

(b) In carbonated drinks containing dissolved carbon dioxide under high pressure, thefollowingdynamicequilibriumexists.

CO aq CO g2 2( ) ( )U

Describe the effect of opening a carbonated drink container and outline how thisequilibriumisaffected. [2]

(c) Thegraphbelowshowshowthevolumeofcarbondioxideformedvarieswithtimewhenahydrochloricacidsolutionisaddedtoexcesscalciumcarbonateinaflask.

V(CO2)

00 Time

(i) Explaintheshapeofthecurve. [3]

(ii) Copytheabovegraphonyouranswersheetandsketchthecurveyouwouldobtainifdoublethevolumeofhydrochloricacidsolutionofhalftheconcentrationasintheexampleaboveisusedinstead,withallothervariableskeptconstantfromtheoriginal.Explainwhytheshapeofthecurveisdifferent. [4]


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(iii) Outlineoneotherwayinwhichtherateofthisreactioncanbestudiedinaschoollaboratory. Sketchagraph to illustratehow the selectedvariablewouldchangewithtime. [2]

(iv) Definethetermactivation energyandstateonereasonwhythereactionbetweencalciumcarbonate andhydrochloric acid takesplace at a reasonably fast rate atroomtemperature. [2]

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7. (a) Alkenesareaneconomicallyandchemicallyimportantfamilyoforganiccompounds.

(i) The reaction of alkenes with bromine water provides a test for unsaturationin the laboratory. Describe the colour change when bromine water is addedtochloroethene. [1]

(ii) Deduce the Lewis structure of chloroethene and identify the formula of therepeatingunitofthepolymerpoly(chloroethene). [2]

(iii) Besidespolymerization,statetwocommercialusesofthereactionsofalkenes. [2]

(b) But-2-enecanbeconvertedtobutan-2-oneintwostages.

(i) Drawthestructuralformulasofbut-2-eneandbutan-2-one. [2]

(ii) Deduceareactionpathwayforthetwostagesofthereaction.Youranswershouldincludethefullybalancedequationforeachstageofthereactionandthereagentsandconditionsforthetwostages. [5]

(c) (i) Deduce thestructural formulasof thetwoalcohol isomersofmolecularformulaC3H8O. Nameeachisomerandidentifyeachaseitheraprimaryorasecondaryalcohol. [3]

(ii) Oxidationofthealcoholisomersleadtotheformationofdifferentorganicproducts.Determinethestructuresoftheorganicproductsformedfromtheoxidationofeachalcoholisomerin(c)(i)aboveandlisttheconditionsrequiredtoobtainthedifferentproducts. [5]

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SECTION A


1. The diagram shows the apparatus used to study the rate of reaction between calcium carbonate and hydrochloric acid.

CaCO (s) 2HCl(aq) CaCl (aq) H O(l) CO (g)3 2 2 2

cotton wool

dilute hydrochloric acidcalcium carbonate

(a) The quantities of reactants added to the flask in one experiment carried out at room temperature were:

mass of single piece of CaCO3(s) = 5.00 g

volume of 1.00 mol dm–3 HCl (aq) = 50.0 cm3

The balance was set to zero at the start of the experiment.

The graph shows how the mass of the flask and contents changed during Experiment 1.

Mass of flask

and contents / g

0.00

Time / min


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(i) Explain why the mass decreased.

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[1]

(ii) Calculate the amount, in moles, of each reactant at the start of Experiment 1.

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[2]

(iii) Use your answers to (a) (ii), and the equation for the reaction, to deduce which reactant was added in excess.

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[1]

(iv) The experiment was repeated with small pieces of calcium carbonate. Draw two lines (labelled 2 and 3) on the graph to show how the mass of the flask and contents

changes in the following experiments at the same temperature.

Experiment Mass of small pieces of CaCO3(s) / g

Volume of 1.00 mol dm–3 HCl (aq) / cm3

2 2.50 50.0

3 5.00 25.0 [4]


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(b) Further experiments were carried out using the reaction in part (a), making only one

change to Experiment 1. In Experiment 4, the mass of small pieces of calcium carbonate

used was 5.00 g. In Experiment 5, the temperature of the mixture was increased by 30 C. In both cases, the reaction was faster than in Experiment 1.

(i) Use the collision theory to explain the main reason why Experiment 4 was faster

than Experiment 1.

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[2]

(ii) Use the collision theory to explain the main reason why Experiment 5 was faster

than Experiment 1.

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[2]

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2. (a) Define the term isotopes.

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[2]

(b) A sample of krypton contains these isotopes.

Isotope Percentage abundance82Kr 15.8084Kr 65.4086Kr 18.80

(i) Calculate the relative atomic mass of krypton in this sample. Give your answer to

two decimal places.

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[2]

(ii) Deduce the number of each sub-atomic particle in an atom of 84Kr.

Protons . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

Neutrons . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

Electrons . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

[2]

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3. (a) Three types of covalent bond (single, double and triple) are present in the molecules in the following equation.

2C H (g) 5O (g) 4CO (g) 2H O(l)2 2 2 2 2

(i) Identify one bond in these molecules that is correctly described by the following.

A polar single bond . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

A polar double bond . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

A non-polar double bond . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

A non-polar triple bond . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

[4]

(ii) Identify the shortest bond in these molecules.

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[1]

(b) The equation for the reaction that occurs when ammonia gas dissolves in water is shown below.

NH (g) H O (l) NH (aq) OH (aq)3 2 4+U

(i) State how the equation indicates that ammonia is a base.

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[1]

(ii) State how the equation indicates that ammonia is a weak base.

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[1]

(iii) Identify which pH value is approximately correct for ammonia solution.

pH 1 3 7 11 13

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[1]


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(c) Complete the table to show the Lewis structure of each ion and the name of the shape of each ion.

NH4+ H3O

+

Lewis structure

Name of shape [4]

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SECTION B


4. (a) (i) Define the term average bond enthalpy. [2]

(ii) Explain why the H–H bond cannot be used as an example to illustrate average bond enthalpy. [1]

(iii) The equation for an important reaction of ethene is given below.

CH2|CH2( ) ( )g O g12 2

O

H2C CH2(g)

Use information from Table 10 in the Data Booklet to calculate the enthalpy change

for this reaction. [3]

(iv) Draw a labelled enthalpy level diagram to represent the reaction in part (a) (iii). [2]

(v) Predict the sign of SÖ for the reaction in part (a) (iii) and explain your choice.

(b) The standard enthalpy changes for the following reactions can be found in Table 13 of the Data Booklet.

C(s) O (g) CO (g)2 2

H (g) O (g) H O(l)212 2 2

C H (l) 12 O (g) 8CO (g) 9H O(l)1812 2 2 28

(i) Use this information to determine the standard enthalpy change for the formation of octane from its elements.

8C(s) 9H (g) C H (l)2 8 18 [4]

(ii) Predict which of the following reactions has the most negative enthalpy change, and explain your choice.

I H (g) O (g) H O(g)212 2 2

II H (g) O (g) H O(l)212 2 2 [2]


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(c) (i) State the name of the energy change represented by GÖ. [1]

(ii) The standard enthalpy and standard entropy changes for a reaction are given below.

CH (g) 2H O(g) 4H (g) CO (g)4 2 2 2 H Ö178 kJ

SÖ 174 J K 1

Explain how the spontaneity of this reaction is affected by changes in temperature. [3]

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5. (a) The reaction between chlorine and bromide ions is a redox reaction.

Cl (g) 2Br (aq) Br (aq) Cl (aq)2 2 2

Define the term oxidation in terms of electron transfer and identify the species that is oxidized in this reaction. [2]

(b) The oxidation number of oxygen is –2 in most compounds containing oxygen. Identify the oxidation numbers of all the other elements in both reactants and products in the following equation.

TiO (s) 2Cl (g) C(s) TiCl (l) CO (g)2 2 4 2 [3]

(c) By referring to oxidation numbers, deduce what happens, if anything, in terms of oxidation and reduction, to the named element in each of these reactions.

(i) Chromium in 2K CrO (aq) 2HCl(aq) K Cr O (aq) 2KCl(aq) H O(l)2 4 2 2 7 2 [2]

(ii) Chlorine in Cl (g) H O(l) HCl(aq) HClO(aq)2 2 [2]

(d) The table shows some reactions involving the metals W, X, Y and Z.

Reaction Reactants Products

1 W + Z(NO3)2 Z + W(NO3)2

2 X + YCl2 no reaction

3 Y + ZSO4 no reaction

4 Z + XO X + ZO

(i) Use the information to arrange the four metals in a reactivity series, starting with the most reactive. Explain with reference to each of the metals how you decided

which metal was the least reactive. [4]

(ii) Metal V forms compounds in which it has an oxidation number of +3. It is more

reactive than any of the metals in the table. Predict the equation for the reaction between metal V and the oxide of metal X. [1]


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V


(e) The diagram shows two half-cells connected together by a salt bridge. The metal in the left-hand cell is more reactive than the metal in the right-hand cell. The reading on the voltmeter is 1.6 V.

magnesium

voltmeter

metal Q

solution of compound P solution of zinc sulfate

(i) Describe the purpose of the salt bridge and identify one substance that might be used in it. [2]

(ii) Identify compound P and metal Q. [2]

(iii) Deduce the half-equation for the reaction in the left-hand cell. [1]

(iv) The voltmeter is replaced by a battery with a voltage of 2.0 V so that the reaction in part (e) (iii) is reversed. Deduce the half-equation for the reaction in the right-hand cell when the battery is connected. [1]

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6. Several straight-chain organic compounds have the molecular formula C4H8O2. Compound A is acidic but compounds B, C and D are neutral liquids with characteristic smells. None of the compounds contain C=C bonds.

(a) (i) Deduce the empirical formula for these compounds. [1]

(ii) Deduce the structural formula and name of compound A. [2]

(iii) State the name of the functional group present in compounds B, C and D. [1]

(b) (i) Compound A can be prepared by the oxidation of butan-1-ol. Identify the reagents

used for the oxidation. Predict the name of the organic compound that can be

formed when butan-1-ol is partially oxidized. Suggest how the reaction can be

controlled to give a low yield of this compound formed by partial oxidation and a

high yield of compound A. [4]

(ii) Compound B is formed when ethanol and ethanoic acid are warmed together. Give the equation for this reaction and name compound B. [2]

(iii) Draw the structural formulas of compounds C and D. [2]

(iv) Predict, with reference to the intermolecular forces in each case, which of the compounds A and B has the higher boiling point. [2]

(c) The compound butan-2-ol exists as optical isomers. Describe the molecular feature

responsible for this and draw 3-dimensional structures for each optical isomer, showing the relationship between them. State how separate samples of each isomer could be distinguished using plane polarized light. [4]

(d) A reaction similar to that in part (b) (ii) occurs when the compounds HOOCC6H4COOH and HOCH2CH2OH react together. Deduce the structure of the repeating unit of the polymer formed. [2]

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SECTION A


1. Bromine and methanoic acid react together in aqueous solution as shown below.

Br (aq) HCOOH (aq) 2HBr (aq) CO (g)2 2

The rate of this reaction was investigated by measuring the change in colour as the bromine was used up. The following graph shows the results of a series of experiments in which 0.010 mol dm 3 Br2 (aq) reacted with a large excess of HCOOH(aq).

Experiments 1 and 2 were carried out at different temperatures. Experiment 3 was carried out at the same temperature as Experiment 1 but in the presence of a catalyst.

(a) The term rate of reaction can be defined as the decrease in the concentration of reactants per unit time. State the alternative definition of rate of reaction.

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[1]

(b) Suggest a different measurement that could be made during this reaction that would also allow the rate of reaction to be investigated.

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[1]


0

0.008

0.004

0.006

0.010

0.002

Time

Experiment 1

Experiment 2

Experiment 3

[Br2] / mol dm–3

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(c) The collision theory can be used to explain the effects of changing conditions on the rate of this reaction.

(i) State two reasons why reactant particles may not react together when they collide.

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[2]

(ii) Identify the experiment (1, 2 or 3) in which the rate of reaction was fastest.

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[1]

(iii) The following Maxwell-Boltzmann graph refers to Experiment 1. Draw another line on the graph that refers to Experiment 2. [2]


Number of

molecules

Energy Ea

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(iv) The following Maxwell-Boltzmann graph refers to Experiment 1. Annotate the graph to show the effect of using the catalyst in Experiment 3. [1]

(v) By referring to the graph in part (c)(iv), explain how the catalyst caused the rate to differ in Experiment 3.

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[2]

Number of

molecules

Energy Ea

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2. (a) A chromium compound contains 28.4 % by mass of sodium, 32.1 % by mass of chromium, the rest being oxygen. Determine the empirical formula of the compound.

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[3]

(b) A sample of the element chromium contains four isotopes, as shown in the table below.

Isotope Relative abundance / %50 Cr 4.3052 Cr 83.853Cr 9.5054 Cr 2.40

Calculate the relative atomic mass of chromium in the sample, giving your answer to two decimal places.

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[2]

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3. Ethanol is manufactured by the hydration of ethene according to the equation below.

C H (g) H O (g) C H OH (g)2 4 2 2 5U

(a) State the expression for the equilibrium constant, Kc, for this reaction.

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[1]

(b) Under certain conditions, the value of Kc for this reaction is 3.7 10 3 1 3 mol dm . When the temperature is increased the value is 4.9 10 4 1 3 mol dm .

(i) State what can be deduced about the position of equilibrium at the higher temperature from these values of Kc.

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[1]

(ii) State what can be deduced about the sign of H for the reaction, explaining your choice.

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[3]

(c) The process used to manufacture ethanol is carried out at high pressure. State and explain two advantages of using high pressure.

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[4]

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4. (a) The approximate pH values of six aqueous solutions are shown in the following table.

Solution A B C D E FpH value 0 1 3 10 13 14

The solutions are listed below. Match each of the solutions with the letter (A, B, C, D, E or F) by writing the letter next to the appropriate solution.

1 0 3. mol dm HCl. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

1 0 3. mol dm NaOH. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

0 1 3. mol dm HNO3 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

0 1 3. mol dm KOH. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

0 1 3. mol dm CH COOH3 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

0 1 3. mol dm NH3 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

[3]

(b) The electrical conductivities of the following solutions were measured.

G 0 1 3. mol dm HCl H 0 1 3. mol dm H SO2 4

I 0 1 3. mol dm CH COOH3

Using the letters G, H and I, list these solutions in decreasing order of electrical conductivity (starting with the best conductor), giving reasons for your choice.

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[3]

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SECTION B


5. (a) (i) But-2-ene, CH CH CH CH3 3, reacts with hydrogen bromide to form a halogenoalkane. Deduce the structural formula of the halogenoalkane and state the type of reaction occurring. [2]

(ii) This halogenoalkane can exist as optical isomers. Explain what is meant by this term and identify the structural feature responsible for this type of isomerism. Outline how these isomers can be distinguished from each other. [4]

(iii) Using information from Table 10 of the Data Booklet, calculate the enthalpy change for the following reaction.

CH CH HBr CH CH Br2 2 3 2

[3]

(b) Butan-1-ol can be converted by acidified potassium dichromate(VI) to either butanal or butanoic acid. Identify the type of reaction occurring and describe the colour change seen during the reaction. Outline the experimental technique needed to produce the maximum amount of butanal and the technique needed to produce the maximum amount of butanoic acid. Explain why these techniques work. [6]

(c) In an esterification reaction butanoic acid, CH CH CH COOH3 2 2 , reacts with methanol, in the presence of a few drops of sulfuric acid, to form two products. Deduce the equation for this reaction, showing the structure of the organic product. [2]

(d) Benzene-1,4-dicarboxylic acid and ethane-1,2-diol react to form a polyester. Explain why these reactants form a polymer, while the reactants in (c) do not. Deduce the structure of the polyester formed. [3]

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6. (a) Using the reaction between lithium and fluorine as an example, describe the formation of an ionic bond. In your answer, refer to the electron arrangements of the species involved, and explain why the product of the reaction has a high melting point. [5]

(b) The product of the reaction between gaseous hydrogen and bromine contains a covalent bond. Draw a Lewis structure for a bromine molecule, and for the product of the reaction. Explain why the product of the reaction has a lower boiling point than bromine. [3]

(c) Table 7 of the Data Booklet contains electronegativity values of elements. Use these values to predict the type of bonding in lithium nitride and chlorine(I) oxide. Write the formula of each compound. [2]

(d) The compound ammonium nitrite (NH4NO2) contains both ionic and covalent bonding. Show how the VSEPR theory can be used to predict the shape of, and bond angle in each of the ions NH4 and NO2. [8]

(e) State and explain which of the two ions in ammonium nitrite is polar. [2]

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7. (a) By referring to electron arrangements and using information from Table 8 of the Data Booklet, explain the difference in radius for each of the following pairs.

(i) Na and Na [2]

(ii) Na and F [2]

(b) By referring to atomic structure and using information from Table 6 of the Data Booklet, explain the difference in melting point for each of the following pairs.

(i) Na and Mg [2]

(ii) F2 and Cl2[2]

(c) The conversion of iron(II) chloride to iron(III) chloride using chlorine gas can be used to illustrate the definitions of the terms oxidation and reduction. Write an equation for this reaction and deduce what is oxidized and reduced, by reference to both electron transfer and oxidation numbers. [5]

(d) Draw a diagram of a cell suitable for the electrolysis of molten lead(II) bromide, PbBr2, and describe the two different ways in which current flows during the electrolysis. Write an equation showing the formation of each of the products. [7]

1010

chemistry sl paper 2 tz1 2009 - exam(iii) explain why the following reaction can also be described...

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