BUFFER__SOLUTION.ppt

buffersolution,departmentofmedicalchemistryyongxianghu,1.whatisabuffersolution,example:in1literpurewateradd0.01molofhydrochloricacid.calculatethissolutionsphchangevalue.andin1litercontain0.1molaceticacidand0.1acetateionmixturesolutionadd0.01molofhydrochloricacid.calculatethissolutionsphchangevalue.notice:squarebracketwillinsteadofequilibriumconcentrationinfollowingtime.suchash+insteadhydrogenionequilibriumconcentration.,step1.calculatethepurewatersphchangevaluethepurewatershydrogenionexponent(ph)value:ph(purewater)=7.00whenaddthehydrochloricacid:h+=0.01mol/1liter=0.01mol.l-1ph=-log0.01=2.00ph=7.002.00=5.00(phunit),step2.calculatecontainaceticacidanditsconjugatebasesolutionsphvalueinthesolutionaceticacidsconcentrationandacetateionsconcentrationhac=0.10mol.l-1ac-=0.10mol.l-1aceticacidequilibrium-constantka=1.7010-5inthissolutionhasaacid-baseequilibriumhach+ac-starting0.100.10,substitutetheconcentrationsintotheequilibrium-constantequationka=h+ac-/hach+=kahac/ac-=1.7010-50.10/0.10=1.7010-5(mol.l-1)ph=4.77,step3.calculatesolutionsphvaluewhenaddhydrochloricacidhach+ac-starting0.100.10change+0.01-0.01equilibrium0.10+0.010.10-0.01step4.substitutetheequilibriumconcentrationintotheequilibrium-constantequationh+=kahac/ac-=1.7010-50.11/0.09=2.0710-5ph=4.68ph=4.774.68=0.09(phunit),definitionofbuffersolution:abuffersolutionisasolutioncharacterizedbytheabilitytoresistchangesinphwhenlimitedamountsofstrongacidorstrongbaseareaddedtoit.,2.compositionofbuffersolutionbuffersolutionconsistofweakacidanditsconjugatebaseorweakbaseanditsconjugateacid.theconjugateacid-basepairarecalledbuffersystemorbufferpair.importantbufferpairsuchas:hac-ac-nh4+-nh3h2co3-hco3-h3po4-h2po4-h2po4-hpo42-hpo42-po43-,3.calculatethephvalueofbuffersolution,henderson-hasselbalchequation:abuffersolutionmadeupofaweakacidhaanditsconjugatebasea-.theacid-ionizationequilib-riumisha(aq)h+(aq)+a-(aq)andtheacid-ionizationconstantiska=h+a-/ha,accordingtotheconstantequation,wecangetanequationfortheh+concentration.h+=kaha/a-takethenegativelogarithmofbothsidesoftheequation.thatis,-logh+=-logkaha/a-=-logkalogha/a-theleftsideequalstheph.thepkaofaweakacidisdefinedinamannersimilartophandpoh.pka=-logka,thepreviousequationcanbewrittenph=pka-logha/a-=pka+loga-/hamoregenerally,wecanwritebaseph=pka+logacidthisisknownasthehenderson-hasselbalchequation.,bufferratio:base/acid,hendersonhasselbalchequationchangeform:,phpka+lgpka+lg,c(conjugatebase)c(conjugateacid),phpka+lgpka+lg,phpka+lgpka+lg,buffercapacityandbuffereffectiverange,buffercapacity()isdefinitedastheamountofsubstanceofstrongacidorstrongbasewhenthephvaluechangeoneunitofphunitin1literofbuffersolution.withdifferentialcoefficient:,=,2.303hbb-/ctotal,(1),(2)0.1mol.l-1hac+naoh,(3)0.2mol.l-1hac+naoh,(4),ph,max2.303(ct/2)(ct/2)/ct0.576ct,cthb+b-,2.303hbb-/ct2.303(hb/ct)(b-/ct)ct2.303(hb/ct)(1-hb-/ct)ct,2.buffereffectiverange,whenthebufferratiois110or101,wecognizethisbuffersolutionwithoutthebufferability.so,wecandefinitethebuffereffectiverangeas:ph=pka1,preparethebuffersolution,principleandstep,choosecorrespondenceofbuffersystem2.thetotalconcentrationofbuffersolution3.calculatetheamountofbuffersolution4.calibratethebuffersolution,tris:trihydrixymethylaminomethane,(hoch2)3cnh2,standardofbuffersolution,potassiumhydrotartrate(khc4h4o6),potassiumacidphthalate(khc8h4o4),borax(na2b4o710h2o),phosphate(kh2po4-na2hpo4),buffersysteminblood,inplasma:h2co3-hco3-、h2po4-hpo42-、hnp-hn-1p-(hnpinsteadofprotein),inredcell:h2b-hb-(h2binsteadofhaemoglobin)、h2bo2-hbo2-(h2bo2insteadofoxyhemoglobin)、h2co3-hco3-、h2po4-hpo42-,co2(solute)+h2oh2co3h+hco3-,phpka，+lg,hco3-co2solute,hco3-co2solute,6.10+lg,inplasma:hco3-=0.024moll-1co2solute=0.0012moll-1,ph6.10+lg6.10+lg7.40,summa,buffersolutioniscomposedofapairofconjugateacid-basepairwithenoughconcentration.thecomponentofanti-acidisconjugatebase.thecomponentofanti-baseisconjugateacid.whenafewstrongacidorbaseisaddedintothebuffersolution.thecomponentofanti-acidandanti-basewillmovetheequilibriumofdissociationtostabilizephvalue.2.wecanusethehenderson-hasselbalchsequationtocalculatethephvalueofbuffersolution:phpka+lgpka+lgpka+lg,3.buffercapacityisdecidedbypan-concentrationandbufferratio.whenthepan-concentrationofthebufferpairissettled,thebufferratioisthemoreclosewithto1,thebuffercapacitywillbethemorelarge.whenthebufferratioisequalto1,thebuffercapacitywillattainthemaximummax.whenthebufferratioisequalization,thepan-concentrationofthebufferpairisthemorelarge,thebuffercapacitywillbethemorelarge.,4.phpka土1isstipulatedthebuffereffectiverange.overthisrange,thebuffersolutionwillbetolosethebufferabilitytoolowofthebuffercapacity.dispensethebuffersolution.itmaybeaccordingtothetableofthisbook.themethodshavethreekinds.thefirstkindis“weakacidadditsconjugatebase”.thesecondkindis“weakacid(overdose)addstrongbase”.thethirdkindis“strongacidaddweakbase(overdose)”.,5.thebuffersolutionapplytomedicalscienceaboutthebuffersystemandbufferactionprincipleinbloo