缓冲溶液(Buffersolutions)解析

Buffersolutionsoutline1Definition2Classification3Howbufferswork4Buffercalculations5Preparationabuffersolution6UsesofthebuffersAbuffersolutionisonewhichtendtoresistchangesinpHwhensmallamountsofacidorbaseareaddedtoitanditspHisnotaffectedbydilution.AcidicbuffersolutionsBasicbuffersolutions•AnacidicbuffersolutionissimplyonewhichhasapHlessthan7.Acidicbuffersolutionsarecommonlymadefromaweakacidandoneofitssalts-oftenasodiumsalt.•Example:AweakacidanditsconjugatebaseCH3CO2H/CH3CO2-(pH=4.76)WecanchangethepHofthebuffersolutionbychangingtheratioofacidtosalt.•AbasicbuffersolutionhasapHgreaterthan7.Basicbuffersolutionsarecommonlymadefromaweakbaseandoneofitssalts.•Example:AweakbaseanditsconjugateacidNH3/NH4+(pH=9.25)WealsocanchangethepHofthebuffersolutionbychangingtheratioofbasetosalt.Abuffersolutionhastocontainthingswhichwillremoveanyhydrogenionsorhydroxideionsthatyoumightaddtoit-otherwisethepHwillchange.Acidicandbasicbuffersolutionsachievethisindifferentways.AcidicbuffersolutionsBasicbuffersolutionsAcidicbuffersolutionsExample:amixtureofaceticacidandsodiumacetatecontainstheseimportantthings:lotsofun-ionisedaceticacid;lotsofacetateionsfromthesodiumacetate;enoughhydrogenionstomakethesolutionacidic.AddinganacidtothisbuffersolutionThebuffersolutionmustremovemostofthenewhydrogenions,otherwisethepHwoulddropmarkedly.Sincemostofthenewhydrogenionsareremoved,thepHwon’tchangeverymuch——butbecauseoftheequilibriuminvolved,itwillfallalittlebit.AddingabasetothisbuffersolutionRemovalbyreactingwithaceticacidBecausemostofthenewhydroxideionsareremoved,thepHdoesn'tincreaseverymuch.RemovalofthehydroxideionsbyreactingwithhydrogenionsBasicbuffersolutionsExample:amixtureofammoniaandammoniumchloridesolutionscontainstheseimportantthings:lotsofunreactedammonia;lotsofammoniumionsfromtheammoniumchloride;enoughhydroxideionstomakethesolutionbasic.AddinganacidtothisbuffersolutionRemovalbyreactingwithammoniaMost,butnotall,ofthehydrogenionswillberemoved.Theammoniumionisweaklyacidic,andsosomeofthehydrogenionswillbereleasedagain.RemovalofthehydrogenionsbyreactingwithhydroxideionsAddingabasetothisbuffersolutionBecausetheammoniaformedisaweakbase,itcanreactwiththewater-andsothereactionisslightlyreversible.Thatmeansmostofthehydroxideionsareremovedfromthesolution.Henderson-HasselbalchequationExample:Throughcalculation,pleasecomparetheadditionsofacidorbasetoabuffersolutionandtopurewater.oneliterofabuffersolution1Minaceticacidand0.3MinsodiumacetateUponadditionof100mlofHCl1M:[CH3CO2H]=(1+0.1)/1.1=1.0Mand[CH3CO2-]=(0.3-0.1)/1.1=0.18MpH=4.76+log(0.18/1)=4.02Uponadditionof100mlofNaOH1M:[CH3CO2H]=(1-0.1)/1.1=0.82M[CH3CO2-]=(0.3+0.1)/1.1=0.36MpH=4.76+lg(0.36/0.82)=4.40OneliterofneutralwaterUponadditionof100mlofHCl1M:[H3O+]=1/1.1=0.091MpH=-log(0.091)=1.04Uponadditionof100mlofNaOH1M:[OH-]=1/1.1=0.091MpOH=-log(0.091)=1.04pH=14-1.04=12.96UsetheHenderson–Hasselbalchequationinreverse.ChooseweakacidwithpKaclosetorequiredpH.SubstituteintoHenderson–Hasselbalchequation.Solvefortheratioof[conjugatebase]/[acid].CommonbuffersolutionssolutionConcentration(mol/L)pH(25℃)KHC4H4O6Saturation,25℃3.557KHC8H4O40.054.008CH3CO2H-CH3CO2Naequalconcentrations4.760KH2PO4-Na2HPO40.025,0.0256.865KH2PO4-Na2HPO40.008695,0.0304307.413Na2B4O7-10H2O0.019.180NH4+-NH3equalconcentrations9.250Example:PreparationofabuffersolutionwithpH=5.2pKa(CH3CO2H/CH3CO2-)=4.76，sothatthismixtureaceticacid(CH3CO2H)/sodiumacetate(CH3CO2-)canbeused.AccordingtotheHenderson-Hasselbalchrelationship:pH=pKa+log([Ac-]/[HAc])5.2=4.76+log([Ac-]/[HAc])0.44=log([Ac-]/[HAc])[Ac-]/[HAc]=10-0.44=2.75mix2.75molesofacetateand1moleofaceticandcompleteto1literwithdistilledwater.UsesofthebuffersolutionThepHofhumanbloodmuststayinarelativelynarrowrangearoundpH=7.4(7.35-7.45),inordertoensurecellularsurvival.Itcanbemaintainedwithintheselimitsthankstobuffersystems.Usingplasmatic(血浆)carbonatesforexample肺肾Buffersarewidelyusedinourdaily-life.Forexample,allinjectionsandeyedropsarebuffered.Furthermore,buffersarealsoimportantinindustry.Thankyou！