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GECH119GECH119SolutionsSolutions

Dr. Ralph C. GatroneDr. Ralph C. GatroneVirginia State UniversityVirginia State University

Department of Chemistry and PhysicsDepartment of Chemistry and Physics

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Chapter ObjectivesChapter Objectives

Ionic BehaviorIonic Behavior Polyatomic IonsPolyatomic Ions Intermolecular InteractionsIntermolecular Interactions SolubilitySolubility ElectrolytesElectrolytes OsmosisOsmosis What is an acid?What is an acid? What is a base?What is a base? Acids react with basesAcids react with bases Acid strengthAcid strength The pH scaleThe pH scale Buffer SolutionsBuffer Solutions

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AssignmentAssignment

Read Chapters 6 and 7 in Read Chapters 6 and 7 in Investigating Investigating Chemistry: A Forensic Science PerspectiveChemistry: A Forensic Science Perspective

For future tests and quizzes you should be For future tests and quizzes you should be able to do problems: 1 – 33 in Chapters 6 able to do problems: 1 – 33 in Chapters 6 and 1 – 16 and 28 in Chapter 7.and 1 – 16 and 28 in Chapter 7.

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Pure SubstancesPure Substances

Pure SubstancesPure Substances– ElementsElements

Consist of atomsConsist of atoms

– Covalent CompoundsCovalent Compounds Consist of moleculesConsist of molecules

– Ionic CompoundsIonic Compounds Consist of IonsConsist of Ions

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Chemical BondingChemical Bonding

Ionic BondingIonic Bonding electromagnetic attraction between ions of electromagnetic attraction between ions of

opposite chargeopposite charge Covalent BondingCovalent Bonding Sharing of electrons between nucleiSharing of electrons between nuclei Polar Covalent BondingPolar Covalent Bonding Unequal sharing of electrons between nucleiUnequal sharing of electrons between nuclei

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Ionic compoundsIonic compounds

Metals on left side form cationsMetals on left side form cations Elements from right side form anionsElements from right side form anions Cations and anions attract forming ionic Cations and anions attract forming ionic

compoundscompounds The charges in ionic compounds must equal The charges in ionic compounds must equal

zero (0)zero (0)

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MummificationMummification

Egyptian process used Egyptian process used NatronNatron to dry body to dry body NatronNatron: sodium carbonate, sodium chloride, : sodium carbonate, sodium chloride,

sodium bicarbonate and sodium sulfatesodium bicarbonate and sodium sulfate

Salt is used to dry (preserve) protein.Salt is used to dry (preserve) protein.

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Salt Dried FishSalt Dried Fish

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QuestionsQuestions

How does salt dry a body?How does salt dry a body?

How does salt absorb water?How does salt absorb water?

Salts behave as desiccants.Salts behave as desiccants.

Desiccants absorb water from surroundings.Desiccants absorb water from surroundings.

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Polarity of WaterPolarity of Water Water has bent structureWater has bent structure Electrons are on one side.Electrons are on one side. Oxygen atom is electronegative.Oxygen atom is electronegative. Forms a dipole with partial charges on each end.Forms a dipole with partial charges on each end.

OH H

positive end

negative end

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NaCl dissolves in waterNaCl dissolves in water Why?Why? NaNa++ attracted to negative end of water (O) attracted to negative end of water (O) ClCl-- attracted to positive end of water (H) attracted to positive end of water (H) Ion – dipole attractionIon – dipole attraction Ions are hydratedIons are hydrated

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Ion Dipole InteractionsIon Dipole Interactions

Weaker than ionic bondsWeaker than ionic bonds Large number of these interactionsLarge number of these interactions Disrupts the ionic bondDisrupts the ionic bond Causes sodium chloride to dissolve in waterCauses sodium chloride to dissolve in water Produces an Produces an aqueous solutionaqueous solution

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NaCl DissolvingNaCl Dissolving

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Molecular InteractionsMolecular Interactions

Before full discussion of solutionsBefore full discussion of solutions Need to discuss molecular interactionsNeed to discuss molecular interactions What are they?What are they? Where do they come from?Where do they come from?

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Attractions Between ParticlesAttractions Between Particles

All attractions are weaker than chemical All attractions are weaker than chemical bondsbonds

What are these attractions?What are these attractions?

How do they arise?How do they arise?

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Attractions Between ParticlesAttractions Between Particles(strength decreases down list)(strength decreases down list)

Ion-dipoleIon-dipole

Dipole – DipoleDipole – Dipole

Dipole – Induced dipoleDipole – Induced dipole

Induced dipole – induced dipoleInduced dipole – induced dipole

Decreasing

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Dipole – Dipole AttractionDipole – Dipole Attraction

Attraction between two polar moleculesAttraction between two polar molecules Hydrogen bondHydrogen bond Occurs between moleculesOccurs between molecules Contain N, O, FContain N, O, F Electronegative atomsElectronegative atoms Greater negativity causes electrons to be Greater negativity causes electrons to be

pulled closer to the atompulled closer to the atom

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Hydrogen BondingHydrogen Bonding

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Strength of H-BondStrength of H-Bond

Variable strengthVariable strength Depends on strength of dipolesDepends on strength of dipoles How strongly nonbonding electrons can attract a How strongly nonbonding electrons can attract a

hydrogenhydrogen Weaker than any covalent bondWeaker than any covalent bond Very pronounced effectVery pronounced effect Structure of waterStructure of water Structure of the DNA moleculeStructure of the DNA molecule

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Induced DipolesInduced Dipoles Nonpolar molecules induced into a dipole Nonpolar molecules induced into a dipole when it approaches a polar moleculewhen it approaches a polar molecule Electrons are pushed by negative end of water moleculeElectrons are pushed by negative end of water molecule Induced dipole dipole attractionInduced dipole dipole attraction Temporary and are very weakTemporary and are very weak Responsible for oxygen dissolving into waterResponsible for oxygen dissolving into water Responsible for COResponsible for CO22 dissolving into water (soda industry) dissolving into water (soda industry)

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Temporary DipolesTemporary Dipoles Randomness of electron motionRandomness of electron motion Can have electrons on one side of a nonpolar Can have electrons on one side of a nonpolar

moleculemolecule Results in a temporary dipoleResults in a temporary dipole

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Induced dipole – induced dipoleInduced dipole – induced dipole

Attraction is the weakest of particle to particle Attraction is the weakest of particle to particle attractionattraction

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Induced dipole – induced dipoleInduced dipole – induced dipole Important in large moleculesImportant in large molecules More space availableMore space available Methane (small molecule) is a gasMethane (small molecule) is a gas Octane (larger molecule) is a liquidOctane (larger molecule) is a liquid

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SolutionsSolutions

Dissolve sucrose Dissolve sucrose molecules into watermolecules into water

Sucrose is pulled into Sucrose is pulled into water by forming water by forming hydrogen bondshydrogen bonds

Homogeneous mixture Homogeneous mixture is producedis produced

single phase (liquid)single phase (liquid) solutionsolution

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SolutionsSolutions

Solid solutionsSolid solutions– Gems, alloysGems, alloys

Liquid solutionsLiquid solutions– Salt water, sugar waterSalt water, sugar water

Gaseous solutionsGaseous solutions– Air (mixture of nitrogen, oxygen, other gases)Air (mixture of nitrogen, oxygen, other gases)

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Solutions – Important TermsSolutions – Important Terms

SolventSolvent – component in the largest amount (water) – component in the largest amount (water) SoluteSolute – the other lesser amount component – the other lesser amount component

(sugar)(sugar) DissolveDissolve ( (DissolvingDissolving) – process of the solute ) – process of the solute

dispersing into the solventdispersing into the solvent SaturatedSaturated – a solution which contains the – a solution which contains the

maximum amount of solutemaximum amount of solute UnsaturatedUnsaturated – a solution which contains less than – a solution which contains less than

the maximum amount of solutethe maximum amount of solute

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Solutions – More TermsSolutions – More Terms

ConcentrationConcentration – the amount of solute – the amount of solute dissolved in an amount of solventdissolved in an amount of solvent

Units of concentrationUnits of concentration can be can be– grams/liter (mass per volume)grams/liter (mass per volume)– moles/liter (number of particles per volume)moles/liter (number of particles per volume)– moles/liter given by the term molarity (M)moles/liter given by the term molarity (M)

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SolubilitySolubility

Ability of a solute to dissolveAbility of a solute to dissolve Solute dissolves easily – solubleSolute dissolves easily – soluble Solute dissolves with difficulty or not at all it Solute dissolves with difficulty or not at all it

is insolubleis insoluble Solubility – determined by interactions Solubility – determined by interactions

between solute particles and solute particles between solute particles and solute particles with the solventwith the solvent

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ExampleExample

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Infinitely SolubleInfinitely Soluble

Ethanol in WaterEthanol in Water Interactions are very similarInteractions are very similar Hydrogen bondsHydrogen bonds Ethanol will dissolve into water in all Ethanol will dissolve into water in all

proportionsproportions Can reach a point where ethanol is the Can reach a point where ethanol is the

solventsolvent

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Effect of TemperatureEffect of Temperature

As T increases solubility generally increasesAs T increases solubility generally increases Increase the motion of moleculesIncrease the motion of molecules Disrupts solute interactionsDisrupts solute interactions Not always the caseNot always the case T has little effect on NaCl dissolvingT has little effect on NaCl dissolving

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Saturated SolutionsSaturated Solutions

Maximum amount of soluteMaximum amount of solute On cooling the solute frequently comes out On cooling the solute frequently comes out

of solutionof solution Solid coming out of solution is called a Solid coming out of solution is called a

precipitateprecipitate We state that the solidWe state that the solid has precipitated has precipitated from from

solventsolvent

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Oxygen in waterOxygen in water

Attraction of molecules is weakAttraction of molecules is weak Dipole – induced dipoleDipole – induced dipole Water hydrogen bonds to waterWater hydrogen bonds to water Strong attractionStrong attraction Oxygen is excludedOxygen is excluded Oxygen is nearly insolubleOxygen is nearly insoluble Sand and water are insolubleSand and water are insoluble Glass and water are insolubleGlass and water are insoluble

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Solutions of GasesSolutions of Gases

Solubility of gases decreases as T Solubility of gases decreases as T increasesincreases

Warm soda loses carbonation faster than Warm soda loses carbonation faster than cold sodacold soda

Observed when you open a warm bottle of Observed when you open a warm bottle of soda – gas escapes more quicklysoda – gas escapes more quickly

Solubility of gases increases with pressureSolubility of gases increases with pressure

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Sudden Sudden release of release of pressure pressure from a from a

carbonated carbonated beverage.beverage.

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Salts in WaterSalts in Water

Salts + water yields ions in waterSalts + water yields ions in water Solution can conduct electricitySolution can conduct electricity Salts and ions called electrolytesSalts and ions called electrolytes Dissolved salts in body fluids maintainDissolved salts in body fluids maintain Blood pressure, neural functions, healthy Blood pressure, neural functions, healthy

cellscells

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Consider the TomatoConsider the Tomato

Growth requiresGrowth requires SunshineSunshine FertilizerFertilizer WaterWater SoilSoil Salt concentration is criticalSalt concentration is critical Too much salt – water is removed from the Too much salt – water is removed from the

tomato leading to deathtomato leading to death

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Tomato PicturesTomato Pictures

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How is water removed?How is water removed?

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OsmosisOsmosis

Movement of water across a semipermeable Movement of water across a semipermeable membrane from a region of low ion concentration membrane from a region of low ion concentration to a region of high ion concentrationto a region of high ion concentration

Semipermeable membrane – permits certain Semipermeable membrane – permits certain molecules to pass throughmolecules to pass through

Ions are surrounded by water and are too large to Ions are surrounded by water and are too large to pass throughpass through

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Cell MembranesCell Membranes

SemipermeableSemipermeable

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The TomatoThe Tomato

High salt concentration in soilHigh salt concentration in soil

Water passes out of tomato into soilWater passes out of tomato into soil

Tomato dries and diesTomato dries and dies

Genetically engineering a salt tolerant Genetically engineering a salt tolerant tomato planttomato plant

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SoapsSoaps

Molecule that has a Molecule that has a polar and nonpolar endpolar and nonpolar end

Polar end dissolves Polar end dissolves into water (polar)into water (polar)

Nonpolar end Nonpolar end dissolves grease dissolves grease (nonpolar)(nonpolar)

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SoapSoap

Polar end interacts with waterPolar end interacts with water Non-polar end interacts with dirtNon-polar end interacts with dirt Combination pulls dirt into waterCombination pulls dirt into water

Polar end must be water solublePolar end must be water soluble Favorable cation is NaFavorable cation is Na+1+1

Water often has lots of CaWater often has lots of Ca+2+2

This soap salt is not soluble in waterThis soap salt is not soluble in water Leads to soap scumLeads to soap scum

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Soap ScumSoap Scum

Hard waterHard water CaCa+2+2 and Mg and Mg+2+2 present present Forms an insoluble salt with soapForms an insoluble salt with soap Soap ScumSoap Scum Bind other anions to form insoluble saltsBind other anions to form insoluble salts Block up pipesBlock up pipes

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Picture of soap scumPicture of soap scum

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Hard water to Soft WaterHard water to Soft Water

Remove CaRemove Ca+2+2 and Mg and Mg+2+2 ionsions

Softens the waterSoftens the water Add CaCOAdd CaCO33: :

done with detergentsdone with detergents

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Water SoftenersWater Softeners

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WaterWater

Autoionization reactionAutoionization reaction HH22O HO H++ + HO + HO--

Concentrations are small in pure waterConcentrations are small in pure water pH used to determine [HpH used to determine [H++]] pH = 7, water is neutralpH = 7, water is neutral Add acid pH decreases Add acid pH decreases (value less than 7)(value less than 7) Add base pH increases Add base pH increases (value greater than 7)(value greater than 7)

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What are Acids?What are Acids?

Bronsted – Lowry definitionBronsted – Lowry definition Acids donate the hydrogen ionAcids donate the hydrogen ion Hydrogen ion (HHydrogen ion (H++) = a proton) = a proton Acids are sour tastingAcids are sour tasting

Common AcidsCommon Acids

Vinegar (acetic acid)Vinegar (acetic acid) Lemons (citric acid)Lemons (citric acid) Vitamin C (ascorbic acid)Vitamin C (ascorbic acid) Bile (hydrochloric acid)Bile (hydrochloric acid)

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What are Bases?What are Bases?

Bronsted – Lowry definitionBronsted – Lowry definition Bases accept the hydrogen ion (HBases accept the hydrogen ion (H++)) Bases taste bitterBases taste bitter Bases have a slippery feelingBases have a slippery feeling Common bases:Common bases: Baking soda (NaHCOBaking soda (NaHCO33))

Drain cleaners (NaOH)Drain cleaners (NaOH)

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Common BasesCommon Bases

NaOH – sodium hydroxideNaOH – sodium hydroxide KOH – potassium hydroxideKOH – potassium hydroxide NHNH33 – ammonia – ammonia

CaO – calcium oxideCaO – calcium oxide

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Acid Base ReactionsAcid Base Reactions

Acids react with basesAcids react with bases Generally acids do not react with acidsGenerally acids do not react with acids Bases do not react with basesBases do not react with bases HH++ is transferred to the base is transferred to the base Example,Example, HCl + HHCl + H22O HO H33OO++ + Cl + Cl--

Water accepts the proton becoming Water accepts the proton becoming Hydronium ionHydronium ion

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Acid – Base BehaviorAcid – Base Behavior

Water can behave as an acid – donates HWater can behave as an acid – donates H++

Water can behave as a base – accepts HWater can behave as a base – accepts H++

Products of acid – base reactionsProducts of acid – base reactions Behave as acids or bases as wellBehave as acids or bases as well HH22O + NHO + NH33 HO HO-- + NH + NH44

++

Reactions are often reversibleReactions are often reversible

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Water acts like an acidWater acts like an acid

HH22O + NHO + NH33 HO HO-- + NH + NH44++

Non-bonding electrons on N accept protonNon-bonding electrons on N accept proton Hydroxide ion formsHydroxide ion forms Ammonium ion formsAmmonium ion forms

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Water acts like a baseWater acts like a base

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The hydroxide ionThe hydroxide ion

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Product from Acid Base ReactionsProduct from Acid Base Reactions

HCl + NaOHHCl + NaOH HCl donates proton to hydroxideHCl donates proton to hydroxide Hydroxide accepts protonHydroxide accepts proton Proton + hydroxide = HOH (water)Proton + hydroxide = HOH (water) Chloride does nothingChloride does nothing Sodium does nothingSodium does nothing NaCl is a saltNaCl is a salt

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SaltsSalts

Salts are less corrosive than the acids and bases Salts are less corrosive than the acids and bases they come fromthey come from

Corrosive chemicalsCorrosive chemicals Property to disintegrate or wear away a surfaceProperty to disintegrate or wear away a surface There are many saltsThere are many salts NaCN – toxic saltNaCN – toxic salt KNOKNO33 – fertilizer (salt peter) and in gun powder – fertilizer (salt peter) and in gun powder

formulationsformulations CaClCaCl22 – de-ice highways – de-ice highways NaF – prevents tooth decayNaF – prevents tooth decay

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Neutralization ReactionsNeutralization Reactions

Acid + baseAcid + base Equal proportionsEqual proportions Yields salt and waterYields salt and water Water is not always the productWater is not always the product HCl + NHHCl + NH33 NH NH44

+ + ClCl--

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Strength of Acids and BasesStrength of Acids and Bases

Stronger acids donate proton easilyStronger acids donate proton easily Stronger bases accept proton easilyStronger bases accept proton easily Add acid to waterAdd acid to water If acid remains, considered weakIf acid remains, considered weak If no acid remains, considered strongIf no acid remains, considered strong Figures show these propertiesFigures show these properties

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Strong AcidStrong Acid

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Weak AcidWeak Acid

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CorrosionCorrosion

How corrosive something dependsHow corrosive something depends Amount of hydronium ion presentAmount of hydronium ion present Dilute solutions of strong acidsDilute solutions of strong acids Less corrosive than more concentratedLess corrosive than more concentrated Fewer hydronium ions presentFewer hydronium ions present True for hydroxide ions from basesTrue for hydroxide ions from bases

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WaterWater

Water behaves as an acidWater behaves as an acid Water behaves as a baseWater behaves as a base Property is called amphotericProperty is called amphoteric Water reacts with itselfWater reacts with itself Gives hydronium and hydroxide ionsGives hydronium and hydroxide ions In pure waterIn pure water [hydronium ion] = [hydroxide ion][hydronium ion] = [hydroxide ion]

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AcidsAcids

What happens when we add an acid to water?What happens when we add an acid to water?

The hydronium ion (HThe hydronium ion (H33OO++) forms.) forms.

Hydroxide ion concentration must decreaseHydroxide ion concentration must decrease

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BasesBases

What happens when we add base?What happens when we add base?

Form hydroxide ionForm hydroxide ion

Hydronium ion concentration must decreaseHydronium ion concentration must decrease

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ConsequenceConsequence

Adding acid, [HAdding acid, [H33OO++] increases] increases

Solution is described as acidicSolution is described as acidic

Adding base, [HOAdding base, [HO--] increases] increases Solution is described as basicSolution is described as basic

Equal amounts, solution is neutralEqual amounts, solution is neutral Adding base to acid is neutralizationAdding base to acid is neutralization

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Measuring AcidityMeasuring Acidity

pH is used to measure aciditypH is used to measure acidity Acidic solutionsAcidic solutions pH is < 7pH is < 7 Basic solutionsBasic solutions pH is > 7pH is > 7 Neutral solutionsNeutral solutions pH = 7pH = 7

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BuffersBuffers

BuffersBuffers Solutions that are resistant to changes in pHSolutions that are resistant to changes in pH Can absorb acid – no pH changeCan absorb acid – no pH change Can absorb base – no pH changeCan absorb base – no pH change Vital to life processesVital to life processes pH of blood kept between 7.35 – 7.45pH of blood kept between 7.35 – 7.45 Proteins denature slightly below and above this pH Proteins denature slightly below and above this pH

valuevalue