医用基础化学英文版PPT课件

Chapter4,BufferSolution,solutionsthatresistchangeinhydroniumion,H+,andthehydroxideion,OH-,concentration(andconsequentlypH)uponadditionofsmallamountsofacidorbase,orupondilution.,4.1.1TheEssentialFeatureofaBuffer,BufferSolution:,4.1CompositionandActionofBufferSolutions,Buffersaremixturescontainingacommonion:eitherweakacidsandtheirconjugatebasesorweakbasesandtheirconjugateacid.Twocommonbuffers:ammonium-ammonia,carbonate-bicarbonateNH4+(aq)H+(aq)+NH3(aq)CO3-2(aq)+H2O(l)HCO3-1(aq)+OH-1(aq),BuffersystemsthatareusefulatvariouspHvalues,Tris:Tris(Hydroxymethy)methanamin,三羟甲基氨基甲烷,ABufferedSolution,resistschangeinitspHwheneitherH+orOHareadded.1.0Lof0.50MCH3COOH+0.50MCH3COONapH=4.74Adding0.010molsolidNaOHraisesthepHofthesolutionto4.76,averyminorchange.,Theeffectofadditionofacidorbaseto,anunbufferedsolution,abufferedsolution,Bufferwithequalconcentrationsofconjugatebaseandacid,OH-,H3O+,BufferafteradditionofH3O+,H2O+CH3COOHH3O+CH3COO-,BufferafteradditionofOH-,4.1.2HowaBufferWorks,HAc+H2O,H3O+Ac,H+,+,Shiftleft,+,OH,H2O,Shiftright,Anti-acid,Anti-base,anti-acidmechanism,anti-basemechanism,TheamountsofweakacidandweakbaseinthebuffermustbesignificantlylargerthantheamountsofH3O+orOH-thatwillbeadded,otherwisethepHcannotremainapproximatelyconstant.Thusadditionoflimitedamountsofastrongacidorbaseiscounteractedbythespeciespresentinthebuffersolution,andthepHchangesverylittle.NosolutioncankeepthepHapproximatelyconstantifyouaddlargeramountsofeitheracidorbasethatarepresentintheoriginalbuffer.,ForaHB-NaBbuffersystem,HB+H2O,H3O+B,NaB,Na+B,Ka=,H+B,HB,H+=Ka,HB,B,Applylogonbothsidesofaboveequation,TheHenderson-HasselbalchEquation,4.2TheHenderson-HasselbalchEquation,ThepHofbuffersolution,pH=pKa+lg,B,HB,=pKa+lg,conjugatebase,conjugateacid,pKa：thelogofKaoftheconjugateacid,B、HB：equilibriumconcentration,B/HB：bufferratio,B+HB：totalconcentration,HB=cHBcHB(dissociated),B=cNaB+cHB(dissociated),cHB,cNaB,TheHenderson-HasselbalchEquation,=pKa+lg,nB/V,nHB/V,Iftheconcentrationsofconjugateacidandbaseusedareequal,i.e.cB=cHB.,pH=pKa+lg,cBVB,cHBVHB,=pKa+lg,VB,VHB,threedifferenttypesofofHenderson-HasselbalchEquation,Fightdilution,CalculatingthepHofaBufferSolution-1,PROBLEM,SampleProblem4-1,Abufferispreparedbymixingequalvolumesof0.1molL-1NaAcand0.2molL-1HAc.WhatisthepHofthefinalsolution?ThepKaofHAcis4.74.WhatwillthepHbeaftertheadditionof0.005molofNaOH(s)to500mLofthebuffersolutiondescribedabove?,SOLUTION,Beforetheadditionof0.005molofNaOH(s)to500mLofthebuffersolution,CalculatingthepHofaBufferSolution-1,SampleProblem4-1,SOLUTION,Aftertheadditionof0.005molofNaOH(s)to500mLofthebuffersolution,CalculatingthepHofaBufferSolution-1,SampleProblem4-1,CalculatingthepHofaBufferSolution-2,PROBLEM,SampleProblem4-2,CalculatethepHofabufferpreparedbymixingHAwithNaA.ThebuffercontainsHAataconcentrationof0.25molL-1.After0.20gNaOHisaddedto100mLofthisbuffer,thepHoftheresultingsolutionis5.60.Theacid-ionizationconstantofHAis5.010-6(pKa=5.3).,SOLUTION,Step1:calculatetheconcentration()ofconjugatebase,MA,inthebufferbeforetheadditionofNaOH,CalculatingthepHofaBufferSolution-2,SampleProblem4-2,SOLUTION,Step2:calculatethepHoftheoriginalbuffer,CalculatingthepHofaBufferSolution-2,SampleProblem4-2,4.3.1TheConceptsofBufferCapacity,BuffercapacityisdefinedastheamountofstrongacidorbaseneededtochangethepHofoneliterofbufferby1unit.,BuffercapacityistheabilitytoresistpHchange.,Or,morespecifically,4.3BufferCapacityandBufferRange,whereisthebuffercapacityandhasunitsofmolesperliterperpH(molL-1pH-1);dna(orb)standsformolesofstrongacidorstrongbasewhichareaddedtoabuffersolutiontocausethechangeinpH,dpH.,Thefollowingcanbederivedfromaboveone：,=2.303HBB/ctotal,unit：molL1pH1,Themagnitudeofindicatestherelativestrengthofbuffercapacity.Thelargerthevalueof,thegreaterthecapacityofthebuffertoresistchangesinpH.,4.3.2FactorsAffectingBufferCapacity,Buffercapacitydependsontwofactor:Relativeone:bufferratio,B/HB.Absoluteone:totalconc.ofbuffer,B+HB,WhenCtotaliffixed：,cB,cHB,=,1,1,(max),cB,cHB,=,10,1,min,cB,cHB,=,1,10,decrease,min,Foragivenbufferpair,themorethebufferratioapproach1,thestrongerthecapacity;whenthebufferratioequals1,thecapacityreachesitsmaximum.,decrease,max=0.576ctotal,Whenthebufferratio,c(B-)/c(HB),isfixed,themoreconcentratedthecomponentsofabuffer,thegreaterthebuffercapacity.,ThepHofabufferisdistinctfromitsbuffercapacity.,Whenthetotalconcentrationofbufferisfixed,themoretheratioofc(B-)/c(HB)approaches1,themorethebuffercapacity.Whenc(B-)/c(HB)=1,thebufferhasthehighestcapacity.,Conclusion:,BufferrangethepHrangeoverwhichthebufferactseffectively.,Buffershaveausablerangewithin1pHunitofthepKaofitsacidcomponent.,4.3.3BufferRange,(max),min,decrease,min,decrease,pH=pKa1,buffereffectiverange,1.Choosetheconjugateacid-basepair.,Calculatetheratioofbuffercomponentconcentrations.,3.Determinethebufferconcentration.,4.MixthesolutionandadjustthepH.,4.4PreparingaBuffer,Generalstepsforabufferpreparation:,AnenvironmentalchemistneedsacarbonatebufferofpH10.00tostudytheeffectsoftheacidrainonlimestone-richsoils.HowmanygramsofNa2CO3mustbeaddedto1.5Loffreshlyprepared0.20MNaHCO3tomakethebuffer?KaofHCO3-is4.7x10-11.,PLAN,WeknowtheKaandtheconjugateacid-basepair.ConvertpHtoH3O+,findthenumberofmolesofcarbonateandconverttomass.,Preparingabuffer-1,PROBLEM,SampleProblem4-3,SOLUTION,HCO3-(aq)+H2O(l)CO32-(aq)+H3O+(aq),pH=10.00;H3O+=1.0 x10-10,CO32-=0.094M,molesofNa2CO3=(1.5L)(0.094mols/L),=0.14,=15gNa2CO3,Preparingabuffer-1,SampleProblem4-3,Method1:,Method2:,WeknowthepHofthebufferis10.0.Theconc.ofNaHCO3is0.20M,UsingHenderson-HasselbalchEquationwecanfindouttheconc.ofCO32-inthebuffer.KaofHCO3-is4.7x10-11.,CO32-=0.094M,molesofNa2CO3=(1.5L)(0.094mols/L),=0.14,=15gNa2CO3,PROBLEM,Preparingabuffer-2,SampleProblem4-4,Thereis2literof0.50molL-1NH3H2Oand2literof0.50molL-1HCl(hydrochloricacid)inalaboratory.AtechnicianwantstousethemtoprepareabufferwithpH=9.00withouttheadditionofwater.Howmanylitersofbuffercanthetechnicianprepareatmost?WhataretheconcentrationsofNH3H2OandNH4+inthebuffer?Thepkb(NH3H2O)=4.74.,SOLUTION,Topreparethebufferwiththevolumeasmoreaspossible,2literof0.500molL-1NH3H2Omustbeutilizedcompletely,whileonlyapartoftheHClcanbeused.,LetthevolumeofHClusedbexL,so,thetotalvolumeofthebufferpreparedis(2.00+x)L.Aftertheneutralization,Preparingabuffer-2,SampleProblem4-4,NH3(aq)+HCl(aq)NH4+(aq)+Cl-(l),Initial(mol)1.00.5V0,change(mol)-0.5V-0.5V+0.5V,Equil-(mol)1.0-0.5V00.5V,V=1.3L,sothebiggestvolumeofbufferis3.3L.,Preparingabuffer-2,SampleProblem4-4,4.5BufferingActioninHumanBlood,ThepHofthebloodinahealthyindividualremainsremarkablyconstantat7.35to7.45.ThisisbecausethebloodcontainsanumberofbuffersthatprotectagainstpHchangeduetothepresenceofacidicorbasicmetabolites.Fromaphysiologicalviewpoint,achangeof0.3pHunitisextreme.Acidmetabolitesareordinarilyproducedingreaterquantitiesthanbasicmetabolites,andcarbondioxideistheprincipalone.昆明癫痫病医院,ThebuffercapacityofbloodforhandlingCO2isestimatedtobedistributedamongvariousbuffersystemsasfollows:hemoglobinandoxyhemoglobin,62%;H2PO4-/HPO42-,22%;plasmaprotein,11%;bicarbonate,5%.Proteinscontaincarboxylic(羧基)andaminogroups,whichareweakacidsandbases,respectively.Theyare,therefore,effectivebufferagents.Thecombinedbuffercapacityofbloodtoneutralizeacidsisdesignatedbycliniciansasthealkalireserve,andthisisfrequentlydeterminedintheclinicallaboratory.Certaindiseasescausedisturbancesintheacidbalanceofthebody.,Forexample,diabetesmaygiveriseto:acidosis,whichcanbefatal.,AnimportantdiagnosticanalysisistheCO2/HCO3-balanceinblood.ThisratioisrelatedtothepHofthebloodbytheHenderson-Hasselbalchequation:,whereH2CO3canbeconsideredequaltotheconcentrationofdissolvedCO2intheblood;6.10ispKa1ofcarbonicacidinbloodatbodytemperature(37).Normally,thebicarbonateconcentrationinbloodisabout26.0mmolL-1,whiletheconcentrationofcarbondioxideis1.3mmolL-1.Accordingly,fortheblood,IfthepHoftheblooddropsbelow7.35,apotentiallyfatalconditioncalledacidosisresults.IfthepHofthebloodincreasestoover7.45,anotherseriousconditionknownasalkalosisresults.,TheHCO3-/H2CO3buffersystemisthemostimportantoneinbufferingbloodinthelung(alveolarblood).Asoxygenfrominhaledaircombineswithhemoglobin,theoxygenatedhemoglobinionizes,releasingaproton.ThisexcessacidisremovedbyreactingwithHCO3-:,Youknowthatcarbonicacidalsobreaksdo