ap chem week 11 ch 4 part c 2018

Recall

Overview• Wecancategorizereactionsintosomegeneraltypes:– Combination/Synthesis– Decomposition– Combustion– RedoxReactions– Singledisplacement/replacement– Doubledisplacement/replacement• PrecipitationReaction• Acid-Base/Neutralization

Acids&Bases

Acids&Bases•  Acids•  AccordingtoArrhenius,acidsionizeinwaterandproduceH+ions

•  AccordingtoBrønsted-Lowry,acidsdonateprotons– Inwater,thisprotonexistsasitshydratedform,hydronium(H3O+)

HClàH++Cl-

HCl(aq)+H2O(l)àH3O+(aq)+Cl-(aq)

Acids&Bases•  PropertiesofAcids:– Sourtaste(ex/vinegar,citrus)– Changethecolorofindicators(ex/litmuspaper)– Areelectrolytes– Reactwithcertainmetalstoproducehydrogengas

2HCl+MgàMgCl2+H2– ReactwithcarbonatestoproduceCO2gas

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

Acids&Bases•  PropertiesofAcids:– Notethatdiprotic(H2SO4)andtriproticacids(H3PO4)havemultipleionizationsteps

– Ex/H3PO4(aq)ßàH+

(aq)+H2PO4-(aq)

H2PO4-(aq)ßàH+

(aq)+HPO42-(aq)

HPO42-(aq)ßàH+

(aq)+PO43-(aq)

Acids&Bases•  Bases•  AccordingtoArrhenius,basesionizeinwaterandproduceOH-ions

•  AccordingtoBrønsted-Lowry,basesacceptprotons

HCl(aq)+H2O(l)àH3O+(aq)+Cl-(aq)

•  Intheequationabove,whatisourbase?

Acids&Bases•  PropertiesofBases:– Bittertaste– Changethecolorofindicators– Areelectrolytes– Feelslippery

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Acid/BaseStrength

Acid/BaseStrength•  Strongacidsarestrongelectrolytes

•  Strongbasesarestrongelectrolytes

•  Thismeansthatweakacidsandweakbasesonlypartiallyionizeinsolution

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Acid-BaseReactions

Neutralization•  Acid-basereactionsareoftencalledneutralizationreactions

•  Generally,aqueousacid-basereactionsproducewaterandasalt:

HCl(aq)+NaOH(aq)àNaCl(aq)+H2O(l)

H+(aq)+Cl-(aq)+Na+(aq)+OH-

(aq)àNa+(aq)+Cl-(aq)+H2O(l)H+

(aq)+OH-(aq)àH2O(l)

•  Whenjustenoughbaseisaddedtoreactexactlywiththeacidinasolution,wesaytheacidhasbeenneutralized

Neutralization•  Warning:weakacidsandbasesdoNOTionizecompletely,thereforetheirnetionicequationslookdifferent:

•  Ex/HCN(aq)+NaOH(aq)àNaCN(aq)+H2O(l)

HCN(aq)+Na+(aq)+OH-(aq)àNa+(aq)+CN-

(aq)+H2O(l)HCN(aq)+OH-

(aq)àCN-(aq)+H2O(l)

Neutralization•  Ex/Whatvolumeofa0.100MHClsolutionisneededtoneutralize25.0mLof0.350MNaOH?

1.  First,writeyourknowns:M=0.350MNaOHV=25.0mLx(1L/1000mL)=0.0250LM=0.100MHClV=?

2.  Second,writeyourbalancedequation:HCl(aq)+NaOH(aq)àNaCl(aq)+H2O(l)

H+(aq)+Cl-(aq)+Na+(aq)+OH-

(aq)àNa+(aq)+Cl-(aq)+H2O(l)H+

(aq)+OH-(aq)àH2O(l)

Neutralization•  Ex/Whatvolumeofa0.100MHClsolutionisneededtoneutralize25.0mLof0.350MNaOH?

3.Usestoichiometry

Neutralization•  Sometimesyou’llneedtofindyourlimitingreactantfirst.

•  Trythis:Inacertainexperiment,28.0mLof0.250MHNO3and53.0mLof0.320MKOHaremixed.WhatistheconcentrationofH+orOH-ionsinexcessafterthereactiongoestocompletion?

Neutralization•  Trythis:Inacertainexperiment,28.0mLof0.250MHNO3and

53.0mLof0.320MKOHaremixed.WhatistheconcentrationofH+orOH-ionsinexcessafterthereactiongoestocompletion?

•  Solution:1.  Writebalancedequation2.  FindmolesofbothH+andOH-thenfindLRtobeH+

3.  FindtheamountofOH-thatreactswithH+is7.00x10-3molOH-

4.  OriginalAmountOH--ConsumedOH-=ExcessOH-1.70x10-2molOH--7.00x10-3molOH-=1.00x10-2molOH-5.  [OH-]=(1.00x10-2molOH-)/(0.0280L+0.0530L)6.  [OH-]=0.123M

Titrations

Titrations•  Anothervolumetricanalysiswecanusetodeterminetheamountofacertainsubstanceisatitration.

•  Inatitration,astandardsolution(ofKNOWNconcentration)isaddedgraduallytoasolutionofunknownconcentrationuntilthechemicalreactioniscomplete.

•  Sinceweknowtheconcentrationandthevolumeaddedofthestandardsolution,aswellasthevolumeoftheunknownsolution,wecancalculatetheconcentrationoftheunknownsolution.

Titrations•  EquipmentRequired:•  Beaker/flask•  Measuringpipetteorburet

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Titrations•  Termstoknow:– Titrant=standardsolution(knownM)– Analyte=substancebeinganalyzed(unknownM)– Equivalencepoint=WhenmolesofOH==molesofH3O+(neutralizationhasoccurred)

–  Indicator=Substanceaddedthatwillundergoacolorchangeneartheequivalencepoint

– Endpoint=Whentheindicatorchangesthecolorofthesolution.Thismaynotmatchtheequivalencepoint,dependingontherangeofpHvalueswheretheindicatorchangescolor

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Titrations•  Acid-BaseTitrationMethod:1.  Analytesolution(ofunknownM)isplacedina

flaskorbeaker2.  Asmallamountofindicatorisadded3.  Titrantisplacedinaburetteandslowlyaddedto

theanalyteandindicatormixture4.  Theprocessisstoppedwhentheindicatorcauses

achangeinthecolorofthesolution5.  Thechangeinvolumeisusedtodeterminethe

volumeoftheanalytesolution

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Titrations•  Note:SometitrationsrequireboilingtogetridofCO2produced,whichwillformcarbonicacid,bufferthesolution,andleadtoinaccuratedata

Titrations•  Ex/Inatitrationexperiment,astudentfindsthat23.48mLofaNaOHsolutionareneededtoneutralize0.5468gofKHP(potassiumhydrogenphthalate,KHC8H4O4).Whatistheconcentration(inmolarity)oftheNaOHsolution?

•  Steps:– Writeyourbalancedequation

KHC8H4O4(aq)+NaOH(aq)àKNaC8H4O4(aq)+H2O(l)– Usestoichiometry

Titrations•  Trythis:HowmanymLofa0.610MNaOHsolutionareneededtoneutralize20.0mLofa0.245MH2SO4solution?

CW•  BookProblems:– Pg.163#17,39,51,53,72,74,77,81,83– ShowallworkJ