缓冲溶液(Buffersolutions)解析课件.ppt

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1、Buffersolutionsoutline1Definition2Classification3Howbufferswork4Buffercalculations5Preparationabuffersolution6UsesofthebuffersAbuffersolutionisonewhichtendtoresistchangesinpHwhensmallamountsofacidorbaseareaddedtoitanditspHisnotaffectedbydilution.Acidic

2、buffersolutionsBasicbuffersolutionsAnacidicbuffersolutionissimplyonewhichhasapHlessthan7.Acidicbuffersolutionsarecommonlymadefromaweakacidandoneofitssalts-oftenasodiumsalt.Example:AweakacidanditsconjugatebaseCH3CO2H/CH3CO2-(pH=4.76)WecanchangethepHofth

3、ebuffersolutionbychangingtheratioofacidtosalt.AbasicbuffersolutionhasapHgreaterthan7.Basicbuffersolutionsarecommonlymadefromaweakbaseandoneofitssalts.Example:AweakbaseanditsconjugateacidNH3/NH4+(pH=9.25)WealsocanchangethepHofthebuffersolutionbychanging

4、theratioofbasetosalt.Abuffersolutionhastocontainthingswhichwillremoveanyhydrogenionsorhydroxideionsthatyoumightaddtoit-otherwisethepHwillchange.Acidicandbasicbuffersolutionsachievethisindifferentways.AcidicbuffersolutionsBasicbuffersolutionsAcidicbuffe

5、rsolutionsExample:amixtureofaceticacidandsodiumacetatecontainstheseimportantthings:lotsofun-ionisedaceticacid;lotsofacetateionsfromthesodiumacetate;enoughhydrogenionstomakethesolutionacidic.AddinganacidtothisbuffersolutionThebuffersolutionmustremovemos

6、tofthenewhydrogenions,otherwisethepHwoulddropmarkedly.Sincemostofthenewhydrogenionsareremoved,thepHwon’tchangeverymuch——butbecauseoftheequilibriuminvolved,itwillfallalittlebit.AddingabasetothisbuffersolutionRemovalbyreactingwithaceticacidBecausemostoft

7、henewhydroxideionsareremoved,thepHdoesn'tincreaseverymuch.RemovalofthehydroxideionsbyreactingwithhydrogenionsBasicbuffersolutionsExample:amixtureofammoniaandammoniumchloridesolutionscontainstheseimportantthings:lotsofunreactedammonia;lotsofammoniumions

8、fromtheammoniumchloride;enoughhydroxideionstomakethesolutionbasic.AddinganacidtothisbuffersolutionRemovalbyreactingwithammoniaMost,butnotall,ofthehydrogenionswillberemoved.Theammoniumionisweaklyacidic,andsosomeofthehydrogenionswillberel