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首页 电化学的有关概念

电化学的有关概念.ppt

电化学的有关概念

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2019-06-15 0人阅读 举报 0 0 暂无简介

简介:本文档为《电化学的有关概念ppt》,可适用于综合领域

电化学的有关概念:电池、电极双电层结构液接电位、盐桥传质过程:扩散、迁移、对流极化:浓差极化、电化学极化过电位PotentiometricMethodsA)Introduction:)PotentiometricMethods:basedonmeasurementsofthepotentialofelectrochemicalcellsintheabsenceofappreciablecurrents(i))BasicComponents:a)referenceelectrode:givesreferenceforpotentialmeasurementb)indicatorelectrode:wherespeciesofinterestismeasuredc)potentialmeasuringdeviceB)ReferenceElectrodes:)NeedoneelectrodeofsystemtoactasareferenceagainstwhichpotentialmeasurementscanbemaderelativecomparisonDesiredCharacteristics:a)knownorfixedpotentialb)constantresponsec)insensitivetocompositionofsolutionunderstudyd)obeysNernestEquatione)reversible)CommonReferenceElectrodesusedinPotentiometrya)CalomelElectrode(HgincontactwithHgClKCl)iSaturatedCalomelElectrode(SCE)verywidelyused½cell:HgHgCl(satd),KCl(xM)||½reaction:HgCl(s)e»HgClNote:responseisdependentonClb)SilverSilverChlorideElectrodemostwidelyusedreferenceelectrodesystemAgelectrodeinKClsolutionsaturatedwithAgCl½cell:AgAgCl(satd),KCl(xM)||½reaction:AgCl(s)e»Ag(s)ClAdvantage–oneadvantageoverSCEisthatAgAgClelectrodecanbeusedattemperatures>oCDisadvantage–Agreactswithmoreionsc)PrecautionsintheUseofReferenceElectrodesneedtokeeplevelofsolutioninreferenceelectrodeabovelevelinanalytesolutionneedtopreventflowofanalytesolutionintoreferenceelectrode‚canresultinpluggingofelectrodeatjunctionerraticbehaviorC)IndicatorElectrodes:)DetectsorRespondstoPresenceofAnalyteThreeCommonTypes:a)MetallicIndicatorElectrodesb)MembraneIndicatorElectrodesc)MolecularSelectiveElectrode)MetallicIndicatorElectrodeFourMainTypes:a)MetallicElectrodesoftheFirstKindiInvolvessinglereactioniiDetectionofcathodederivedfromthemetalusedintheelectrodeiiiExample:useofcopperelectrodetodetectCuinsolution½reaction:Cue»Cu(s)EindgivesdirectmeasureofCu:Eind=EoCu–()logaCu(s)aCusinceaCu(s)=:Eind=EoCu–()logaCuorusingpCu=logaCu:Eind=EoCu–()pCuivProblems:notveryselectivemanycanonlybeusedatneutralpHmetalsdissolveinacidssomemetalsreadilyoxidizecertainhardmetals(Fe,Cr,Co,Ni)donotyieldreproducibleresultspXversusactivitydiffersignificantlyandirregularlyfromtheoryb)MetallicElectrodesoftheSecondKindiDetectionofanionderivedfromtheinteractionwithmetalion(Mn)fromtheelectrodeiiAnionformsprecipitateorstablecomplexwithmetalion(Mn)iiiExample:DetectionofClwithAgelectrode½reaction:AgCl(s)e»Ag(s)ClEO=VEindgivesdirectmeasureofCl:Eind=EoCu–()logaAg(s)aClaAgCl(s)sinceaAg(s)andaAgCl(s)=Eo=V:Eind=–()logaClivAnotherExample:DetectionofEDTAion(Y)withHgElectrode½reaction:HgYe»Hg(l)YEo=VEindrespondstoaY:Eind=Eo–()logaHg(l)aYaHgYsinceaHg(l)=andEo=V:Eind=–()logaYaHgYc)MetallicElectrodesoftheThirdKindiMetalelectrodesrespondstoadifferentcationiiLinkedtocationbyanintermediatereactionAlreadysawdetectionofEDTAbyHgelectrode(ndKind)iiCanbemadetodetectothercationsthatbindtoEDTAaffectingaYivExample:DetectCabycomplexwithEDTAequilibriumreaction:CaY»CaYWhere:Kf=ˆEind=–()logaYaHgYacaaYaCaYay=KfacaaCaYNote:aYandEindnowalsochangeswithaCad)MetallicRedoxIndicatorsiElectrodesmadefrominertmetals(Pt,Au,Pd)iiUsedtodetectoxidationreductioninsolutioniiiElectrodeactsasesourcesinkivExample:DetectionofCewithPtelectrode½reaction:Cee»CeEindrespondstoCe:Eind=Eo–()logaCeaCevProblems:electrontransferprocessesatinertelectrodesarefrequentlynotreversibledonotrespondpredictablyto½reactionsintables)MembraneIndicatorElectrodesa)GeneralielectrodesbasedondeterminationofcationsoranionsbytheselectiveadsorptionoftheseionstoamembranesurfaceiiOftencalledIonSelectiveElectrodes(ISE)orpIonElectrodesiiiDesiredpropertiesofISE’s‚minimalsolubility–membranewillnotdissolveinsolutionduringmeasurement–silica,polymers,lowsolubilityinorganiccompounds(AgX)canbeused‚Needsomeelectricalconductivity‚Selectivelybindsionofinterestb)pHElectrodeimostcommonexampleofanISE‚basedonuseofglassmembranethatpreferentiallybindsHiiTypicalpHelectrodesystemisshown‚Tworeferenceelectrodeshere‚oneSCEoutsideofmembrane‚oneAgAgClinsidemembrane‚pHsensingelementisglasstipofAgAgClelectrodeiiipHisdeterminedbyformationofboundarypotentialacrossglassmembraneAteachmembranesolventinterface,asmalllocalpotentialdevelopsduetothepreferentialadsorptionofHontotheglasssurfaceBoundarypotentialdifference(Eb)=E=EwherefromNernstEquation:Eb=c–pHGlassSurfacelogaH(onexteriorofprobeorinanalytesolution)constantivAlkaliError‚HnotonlycationthatcanbindtoglasssurfaceHgenerallyhasthestrongestbinding‚GetweakbindingofNa,K,etc‚MostsignificantwhenHoraHislow(highpH)usuallypH$AtlowaH(highpH),amountofNaorKbindingissignificantincreasesthe“apparent”amountofboundHvAcidError‚ErrorsatlowpH(Aciderror)cangivereadingsthataretoohigh‚ExactcausenotknownusuallyoccursatpH#c)GlassElectrodesforOtherCationsichangecompositionofglassmembrane‚puttingAlOorBOinglass‚enhancesbindingforionsotherthanHiiUsedtomakeISE’sforNa,Li,NHd)CrystallineMembraneElectrodeiFluorideElectrode‚LaFcrystaldopedwithEuF‚mechanismsimilartopHelectrodewithpotentialdevelopingattwointerfacesofthemembranefromthereaction:LaF»LaFFSolid(membranesurface)SolutionˆthesideofthemembranewiththeloweraFbecomespositiverelativetotheothersurface:Eind=c–pFe)LiquidMembraneElectrode‚“Membrane”usuallyconsistsoforganicliquid(notsolubleinsample)heldbyporousdiskbetweenaqueousreferencesolutionandaqueoussamplesolution‚MembranehasabilitytoselectivelybindionsofinterestExample:CalciumdialkylphosphateLiquidmembraneelectrodesAtsolutionmembraneinterfaces:(RO)POOCa»(RO)POOCaOrganic(membrane)Organic(membranesurface)Solution(aqueoussample)ˆthesideofthemembranewiththeloweraCabecomesnegativerelativetotheothersurface:Eind=c–pCae)LiquidMembraneElectrode‚CandesignLiquidMembraneElectrodesforeithercationsoranionscationsusecationexchangersinmembraneanionsuseanionexchangersinmembranef)MolecularSelectiveElectrodesiElectrodesdesignedforthedetectionofmoleculesinsteadofionsiiGassensingelectrodes(orgassensingprobes)‚TypicallybasedonISEsurroundedbyelectrolytesolutionactivityofionmeasuredisaffectedbydissolvedgasgasentersinteriorsolutionfromsamplebypassingthroughagaspermeablemembraneGaseffusesthroughmembrane:CO(aq)»CO(g)»CO(aq)externalmembraneinternalsolutionporessolutionIninternalsolution,pHchanges:CO(aq)HO»HCOHwhichisdetectedbyISEprobeOverallreaction:CO(aq)HO»HHCOexternalinternalsolutionsolutionEind=clogCOextiiiEnzymeelectrodes(orBiocatalyticMembraneElectrodes)‚Generalapproachistouseanimmobilizedenzymeenzymeconvertsagivenmolecularanalyteintoaspeciesthatcanbemeasuredelectrochemically<enzymesubstrateExamples:HpHelectrodeCOCOgassensingelectrodeNHNHISE‚Example–UreaEnzymeElectrodePrincipal:Inpresenceofenzymeurease,urea(NH)COishydrolyzedtogiveNHandHMonitoramountofNHproducedusingNHgassensingelectrodeApplicationsDirectpotentiometryPotentiometricTitrationsDirectpotentiometryPotentiometricTitrationsDeterminationofacidwithNaOH(pH)DeterminationofCl–withAgNO(AgCl,AgISE)DeterminationofAlwithNaF(AlF–,F–ISE)DeterminationofFewithKCrO(Fe,Pt)WhatwouldEvsVolumecurveslooklike思考题推导式子:Eb=c–pH直接电位法的校正曲线法、标准加入法为什么要使用总离子强度调节液电位滴定法的滴定曲线及终点的确定实验水中氟离子的测定--离子选择性电极法

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