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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