资源描述：
《APChemistryLab-Edline：AP化学实验室Edline》由会员上传分享，免费在线阅读，更多相关内容在工程资料-天天文库。
1、Purpose:DeterminationoftheKaofWeakAcids-TodeterminetheKaforaknownmonoproticweakacidfromitspHvalue・TodeterminetheKaforanunknownmonoproticweakacidbytitrationBackgroundInformation:Acidsandbasesareimportantclassesofchemicalcompounds.TheycontrolthepHofbiologicalsyste
2、msandparticipateinmanyindustrialreactions.Inaddition,theyacttoexacerbatemanyunwantedreactions,resultinginsubstantialfinanciallosestoconsumers.Anunderstandingofacidsandbasesisthereforeparamounttounderstandingchemistry.Weakacidsarethosethatdissociatepartiallyaccor
3、dingtothefollowing:TheaciddissociationconstantKaisanexpressionfortheamountofdissociatiori・ItcanbefoundbyKa=[H+][A][HA]Thus,ifyouknowtheoriginalconcerttrationoftheweakacidandcandeterminethe[H+],thenKacanbedetermined.The[H]canbeascertainedwiththeuseofapHmeterwhich
4、worksontheprincipalofavoltagedifferencebetweentheinsideoftheprobeandthesolution.Theacidequilibriumconstantforthereaction,Ka,providesaquantitativemeasureofthedegreetowhichanaciddissociates.Asma11valueforKa(<<1)indicatesthattheacidremainsmostlyasmoleculesinsolutio
5、n.Ontheotherhand,aIargevalueforKa(>>1)indicatesthattheacidhasdissociatedtoagreaterextent.Infact」nthecaseofastrongacidsuchasHCIthereisessentiallynomolecularacidremaininginsolution,andKaisinfinite.WhenaweakacidisIabeled,forexampie,as0.1OOM,thisreferstotheinitiaImo
6、larityoftheacid,beforeanyofitdissociates・Thustheactualconcentrationofundissociatedacidwi11alwaysbelessthanthestatedvalue・TheamountthathasdissociatedcanbedeterminedbymeasuringthepHofthesolution.Asoutlinedinyouracidbackgroundreading,ifonetitrateshalfoftheunknownac
7、idsolutiontocompletion,thenthereisnoremainingHAspeciesinsolution;onlyA'salttitrated.Byaddingthisbacktothehalfnottitrated,theA'saltfromtitration=HAaciduntitrated・TheKoftheunknownsolutioncanbeeasilydeterminedatthispoint,as[H1]=K.The[H*]concentrationofthemixturecan
8、bedeterminedusingapHprobe・Materials:pHmeter,labprodevice,loggerpro,unknownmonoproticacid,buffersolutionsofpH4,7,10,distilledwater,100mLgraduatedcyIinders,standardized
