FLT•  Iwillbeableto:–  Explaintherelativestrengthsofacidsandbasesbasedonmolecularstructure,

interparticleforces,andsolutionequilibrium–  IdentifycompoundsasBrønsted-Lowryacids,bases,and/orconjugateacid-

basepairs,usingproton-transferreactionstojustifytheidentification–  Generateoruseaparticulaterepresentationofanacid(strongorweakor

polyprotic)andastrongbasetoexplainthespeciesthatwillhavealargeversussmallconcentrationsatequilibrium

–  ReasonaboutthedistinctionbetweenstrongandweakacidsolutionswithsimilarvaluesofpH,includingthepercentionizationoftheacids,theconcentrationsneededtoachievethesamepH,andtheamountofbaseneededtoreachtheequivalencepointinatitration

–  Reasonthatneutrality,basedonthedependenceofKWontemperature,requires[H+]=[OH-]asopposedtorequiringpH=7,includingespeciallytheapplicationstobiologicalsystems

–  Identifyagivensolutionasbeingthesolutionofamonoproticweakacidorbase(includingsaltsinwhichoneisaweakacidorbase),calculatethepHandconcentrationofallspeciesinthesolution,and/orinfertherelativestrengthsoftheweakacidsorbasesfromgivenequilibriumconcentrations

bycompletingCh.14NotesA

Ch.14:AcidsandBases

Recall

8

Electrolytes

9

Electrolytes and Nonelectrolytes •  Electrolytes=Dissolveintoions&conductelectricityinaq.soln.

Electrolytes and Nonelectrolytes • Nonelectrolytes=Donotconductelectricityinaq.soln.

• Mostaremolecular/covalent(noions)

Electrolytes and Nonelectrolytes • Notallelectrolytesconducttothesamedegree

•  Thereareweakelectrolytes,andstrongelectrolytes

•  Dependson:thedegreeofionization• Weakelectrolytesonlypartiallyionize.

Electrolytes and Nonelectrolytes •  Weakelectrolytes=onlypartiallyionizeWeakelectrolyteshaveonlyafractionofthesolutethatexistsasions(about1%)– Weakacidsandbases;ammonia,aceticacid

Acids&Bases

Acids&Bases•  PropertiesofAcids:

– Sourtaste(ex/vinegar,citrus)– Changethecolorofindicators

•  Turnbluelitmuspaperred

– Electrolytes– Candissolvemanymetals– Reactwithcertainmetalstoproducehydrogengas

2HCl+MgàMgCl2+H2– ReactwithcarbonatestoproduceCO2gas

2HCl+CaCO3àCaCl2+H2O+CO2– Reactwithbases(neutralizationreactions)

Tro,Chemistry:AMolecularApproach 16

CommonAcidsChemical Name Formula Uses Strength

Nitric Acid HNO3 explosive, fertilizer, dye, glue Strong

Sulfuric Acid H2SO4 explosive, fertilizer, dye, glue,

batteries Strong

Hydrochloric Acid HCl metal cleaning, food prep, ore refining, stomach acid Strong

Phosphoric Acid H3PO4 fertilizer, plastics & rubber,

food preservation Moderate

Acetic Acid HC2H3O2 plastics & rubber, food preservation, Vinegar Weak

Hydrofluoric Acid HF metal cleaning, glass etching Weak

Carbonic Acid H2CO3 soda water Weak

Boric Acid H3BO3 eye wash Weak

Tro,Chemistry:AMolecularApproach 17

StructureofAcids•  oxyacidshaveacidhydrogensattachedtoanoxygenatom– H2SO4,HNO3

Tro,Chemistry:AMolecularApproach 18

StructureofAcids•  carboxylicacidshaveCOOHgroup–  HC2H3O2,H3C6H5O7

•  onlythefirstHintheformulaisacidic–  theHisontheCOOH

Acids&Bases•  PropertiesofBases:

– Bittertaste– Slipperyfeel– Changethecolorofindicators

•  Turnredlitmuspaperblue

– Areelectrolytes– Canneutralizeacids

Acids&Bases•  Alkaloidsarenaturallyoccurringorganicbases,suchasthosefoundinplants,thatoftenhaveasignificantphysiologicalaffectonhumans

Tro,Chemistry:AMolecularApproach 21

CommonBasesChemical

Name Formula Common Name Uses Strength

sodium hydroxide NaOH lye,

caustic soda soap, plastic,

petrol refining Strong

potassium hydroxide KOH caustic potash soap, cotton,

electroplating Strong

calcium hydroxide Ca(OH)2 slaked lime cement Strong

sodium bicarbonate NaHCO3 baking soda cooking, antacid Weak

magnesium hydroxide Mg(OH)2

milk of magnesia antacid Weak

ammonium hydroxide

NH4OH, {NH3(aq)}

ammonia water

detergent, fertilizer,

explosives, fibers Weak

Acids&Bases•  Canwerecognizethestructureofbases?

• MostionicbasescontainOH-ions– NaOH,Ca(OH)2

•  SomecontainCO32-ions

– CaCO3,NaHCO3• MolecularbasescontainstructuresthatreactwithH+– Mostlyaminegroups

DefinitionsofAcidsandBases

DefinitionsofAcids&Bases1.  Arrhenius2.  Brønsted-Lowry3.  Lewis“Thedifferencesbetweenthevariousacid-baseconceptsarenotconcernedwithwhichisright,

butwhichismostconvenienttouseinaparticularsituation.”

-JamesHuheey

TheArrheniusDefinition

TheArrheniusDefinition•  SvanteArrhenius(1880s)•  Acid

– AsubstancethatproducesH+ionsinaqueoussolution

•  Base– AsubstancethatproducesOH-ionsinaqueoussolution

ArrheniusTheory

HClionizesinwater,producingH+andCl–ions

NaOHdissociatesinwater,producingNa+andOH–ions

TheArrheniusDefinition•  Note:•  TheH+ionsarehighlyreactiveinaqueoussolution,andtheybondtowatertoformH3O+

•  Consequently,H+(aq)andH3O+

(aq)aresometimesusedinterchangeablywhendiscussingaqueoussolutions

Brønsted-LowryDefinition

TheBrønsted-LowryDefinition•  1923•  Morewidelyapplicabledefinition•  Looksatthetransferofprotons(H+)inanacid-basereaction

•  Acid=protondonor•  Base=protonacceptor•  Inthisdefinition,acidsandbasesalwaysoccurtogether

TheBrønsted-LowryDefinition•  Wecanlabelouracid-basereactionsusingproton-transfer

•  Ex1:

HCl(aq)+H2O(l)àH3O+(aq)+Cl-(aq)

•  Ex2:

NH3(aq)+H2O(l)ßàNH4+(aq)+OH-

(aq)

Donated(Lost)H+

Donated(Lost)H+

Accepted(gained)H+

Accepted(gained)H+

Acid

Acid

Base

Base

TheBrønsted-LowryDefinition•  AmphotericSubstances

– Substancesthatcanactasacidsorbases– Example:H2O

TheBrønsted-LowryDefinition•  ConjugateAcid-BasePairs

– Twosubstancesrelatedtoeachotherbythetransferofaproton

•  ConjugateAcid– Speciesformedafterabasehasacceptedaproton– Functionsastheacidinthebackreaction

•  ConjugateBase– Speciesformedafteranaciddonatesaproton– Functionsasthebaseinthebackreaction

HCl(aq)+H2O(l)àH3O+(aq)+Cl-(aq)

TryThis:•  IdentifyandLabelallspecies:

HCO3-(aq)+H2O(l)ßàH2CO3(aq)+OH-

(aq)

H2SO4(aq)+H2O(l)ßàHSO4-(aq)+H3O+

(aq)

AcidStrength&theAcidIonizationConstant(Ka)

AcidStrengthandKa•  Recall:– Astrongacidisastrongelectrolyte,andaweakacidisaweakelectrolyte

•  Inotherwords,thestrengthofanaciddependsontheequilibrium

HA(aq)+H2O(l)ßàH3O+(aq)+A-

(aq)•  Iftheequilibriumliesfartotheright,theacidisstrongbecauseitcompletelyionizes.Iftheequilibriumliestotheleft,theacidisweakbecauseonlyasmall%oftheacidmoleculesionize

ArrowConventions•  chemistscommonlyusetwokindsofarrowsinreactionstoindicatethedegreeofcompletionofthereactions

•  asinglearrowindicatesallthereactantmoleculesareconvertedtoproductmoleculesattheend

•  adoublearrowindicatesthereactionstopswhenonlysomeofthereactantmoleculeshavebeenconvertedintoproducts

AcidStrengthandKa•  StrongacidsaremorewillingtodonateH•  StrongacidsdonatepracticallyalloftheirH’s

– 100%ionizedinwater•  [H3O+]=[strongacid]•  Examples:•  HCl•  HBr•  HI•  HNO3•  HClO4

•  H2SO4

HCl→H++Cl-

HCl+H2O→H3O++Cl-

AcidStrengthandKa•  WeakacidsdonatesmallfractionofH’s•  Lessthan1%ionizedinwater•  [H3O+]<<[acid]

•  Examples:•  HF•  HC2H3O2(acetic)•  HCHO2(formic)•  H2SO3(sulfurous)•  H2CO3(carbonic)•  H3PO4(phosphoric)

HF⇔H++F-HF+H2O⇔H3O++F-

Tro,Chemistry:AMolecularApproach 40

Acids Conjugate Bases HClO4 ClO4

-1 H2SO4 HSO4

-1 HI I-1

HBr Br-1 HCl Cl-1

HNO3 NO3-1

H3O+1 H2O HSO4

-1 SO4-2

H2SO3 HSO3-1

H3PO4 H2PO4-1

HNO2 NO2-1

HF F-1 HC2H3O2 C2H3O2

-1 H2CO3 HCO3

-1 H2S HS-1

NH4+1 NH3

HCN CN-1 HCO3

-1 CO3-2

HS-1 S-2 H2O OH-1

CH3-C(O)-CH3 CH3-C(O)-CH2-1

NH3 NH2-1

CH4 CH3-1

OH-1 O-2

Increasin

gAcidity

IncreasingBasicity

AcidStrengthandKa•  Thedegreetowhichanacidisstrongorweakdependsontheattractionbetweentheanionoftheacid(conjugatebase)andthehydrogenion,relativetotheattractionsoftheseionstowater

HA(aq)+H2O(l)ßàH3O+(aq)+A-

(aq)•  IftheattractionsbetweenH+andA-isweak,thentherxnfavorstheforwarddirection,andtheacidisstrong

•  Iftheattractionb/tH+andA-isstrong,thentherxnfavorsthebackdirection,andtheacidisweak

AcidStrengthandKa•  Generallyspeaking,thestrongertheacid,theweakertheconjugatebaseandviceversa

•  Iftheforwardreactionhasahightendencytooccur,thenthereversereactionhasalowtendencytooccur

GeneralTrendsinAcidity•  ThestrongeranacidisatdonatingH,theweakertheconjugatebaseisatacceptingH

•  higheroxidationnumber=strongeroxyacid– H2SO4>H2SO3;HNO3>HNO2

•  cationstrongeracidthanneutralmolecule;neutralstrongeracidthananion– H3O+1>H2O>OH-1;NH4

+1>NH3>NH2-1

– basetrendopposite

AcidStrengthandKa•  Awordofwarning…•  Donotconfusetheterms“strong”and/or“weak”with“concentrated”and“diluted”.

TheAcidIonizationConstant(Ka)

TheAcidIonizationConstant(Ka)•  Ka=Acidionizationconstant=theequilibriumconstantfortheionizationreactionofaweakacid

•  GivenHA(aq)+H2O(l)ßàH3O+

(aq)+A-(aq)

or

HA(aq)ßàH+(aq)+A-

(aq)•  Then

Ka= =

[H3O+][A-]

[HA]

[H+][A-]

[HA]

TheAcidIonizationConstant(Ka)•  Forweakacids,Kashouldberelativelysmall