chapter 4 acid-base__ titrimetry

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1、Chapter3TitrimetricAnalysis3.2Acid-BaseTitration3.2.1Acid-BaseEquilibria1)Acid-BaseTheory2)PBE＆pHCalculation3)DistributionCoefficient3.2.2TitrationCurves3.3.3Acid-BaseIndicators3.3.4ApplicationsAcid-BaseTitrationThisisaquickaccuratemethodfordeterminingacidicorbasicsubstancesinmanys

2、amples.SeveralinorganicacidsandbasesHundredsoforganicspeciesThistitrantistypicallyastrongacidorbase.Thesamplespeciescanbeeitherastrongorweakacidorbase.3.2.1Acid-BaseEquilibria1.Acid-BaseTheory★ArrheniusTheory(NobelPrize1903)Acid:anysubstancethationizesinwatertogivehydrogenions(H+).

3、Hydrogenionsassociateswiththesolventtoincreasehydroniumion(H3O+)insolution.Base:ionizesinwatertogivehydroxylions(OH-)★BrØnsted–LowryTheoryAcid=ProtonDonorBase=ProtonAcceptorAcidBaseAcidBaseHCl+H2OH3O++Cl-(Strong)(Weak)H2CO3+H2OH3O++HCO3-(Weak)(Strong)ABrønstedacidisaprotondonor.A

4、Brønstedbaseisaprotonacceptor.Acid=H++BaseTheseareconjugatepairs.A“strong”electrolyteiscompletelydissociated.A“weak”electrolyteispartiallydissociated.AcidDissociationConstantBaseDissociationConstantHA+H2O==H3O++A-A-+H2O==HA+OH-Foranyacid-basepair:KaKb=[H+][A-][HA][HA][OH-][A-]=KwSt

5、rongacid----Ka↑Strongbase----Kb↑Weakacid-----Ka↓Weakbase-----Kb↓H3A=H++H2A-H2A-=H++HA2-HA2-=H++A3-ForPolyproticAcids:A3-+H2O=HA2-+OH-HA2-+H2O=H2A-+OH-H2A-+H2O=H3A+OH-ForitsConjugateBases:Ka1Kb3=Ka2Kb2=Ka3Kb1=KwconclusionForPolyproticAcids:H3PO4H2PO4-HPO42-PO43-Kb2Kb1Kb3Ka1Ka2Ka3

6、3.2.1Acid-BaseEquilibria2.CalculationofpHpH=-lg[H+]pHistheacidityexpressionofanaqueoussolution:25℃◆[H+]=1.0×10-7mol/LpH=7.00◆[OH-]=1.0×10-3mol/L[H+]=1.0×10-11mol/LpH=11.00(1)Protonbalanceequation(PBE)a)[H+]obtained=[H+]lostb)SelectingzerolevelsJudgingthespeciesthatloseprotonsandobt

7、ainprotonsd)WritingthePBEequationExampleWritethePBEfortheacidHAsolutionInthesolution：thespeciesthatarepresentinsufficientamountareHA,H2OHA+H2O==H3O++A-H2O+H2O==H3O++OH-PBE:[H3O+]==[A-]+[OH-]notcontainingHA,H2OAnotherExampleWritethePBEfortheNa2CO3solutionInthesolution：thespeciesthat

8、arepresentinsufficientamou