电化学的有关概念课件.ppt

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1、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:1.)PotentiometricMethods:basedonmeasurementsofthepotentialofelectrochemicalcellsintheabsenceofappreciablecurrents(i.0)2.)BasicComponents:a)referenceelectrode:givesreferenc

2、eforpotentialmeasurementb)indicatorelectrode:wherespeciesofinterestismeasuredc)potentialmeasuringdeviceB.)ReferenceElectrodes:1.)Needoneelectrodeofsystemtoactasareferenceagainstwhichpotentialmeasurementscanbemaderelativecomparison.DesiredCharacteristics:a)knowno

3、rfixedpotentialb)constantresponsec)insensitivetocompositionofsolutionunderstudyd)obeysNernestEquatione)reversible.2.)CommonReferenceElectrodesusedinPotentiometrya)CalomelElectrode(HgincontactwithHg2Cl2&KCl)i.SaturatedCalomelElectrode(SCE)verywidelyused½cell:Hg/Hg

4、2Cl2(satd),KCl(xM)

5、

6、½reaction:Hg2Cl2(s)+2e-»2Hg++2Cl-Note:responseisdependenton[Cl-]b)Silver/SilverChlorideElectrode-mostwidelyusedreferenceelectrodesystem-AgelectrodeinKClsolutionsaturatedwithAgCl½cell:Ag/AgCl(satd),KCl(xM)

7、

8、½reaction:AgCl(s)+e-»Ag(s)+Cl-Advanta

9、ge–oneadvantageoverSCEisthatAg/AgClelectrodecanbeusedattemperatures>60oCDisadvantage–Agreactswithmoreionsc)PrecautionsintheUseofReferenceElectrodes-needtokeeplevelofsolutioninreferenceelectrodeabovelevelinanalytesolution-needtopreventflowofanalytesolutionintorefe

10、renceelectrode‚canresultinpluggingofelectrodeatjunctionerraticbehaviorC.)IndicatorElectrodes:1.)DetectsorRespondstoPresenceofAnalyteThreeCommonTypes:a)MetallicIndicatorElectrodesb)MembraneIndicatorElectrodesc)MolecularSelectiveElectrode2.)MetallicIndicatorElectr

11、odeFourMainTypes:a)MetallicElectrodesoftheFirstKindi.Involvessinglereactionii.Detectionofcathodederivedfromthemetalusedintheelectrodeiii.Example:useofcopperelectrodetodetectCu2+insolution½reaction:Cu2++2e-»Cu(s)EindgivesdirectmeasureofCu2+:Eind=EoCu–(0.0592/2)log

12、aCu(s)/aCu2+sinceaCu(s)=1:Eind=EoCu–(0.0592/2)log1/aCu2+orusingpCu=-logaCu2+:Eind=EoCu–(0.0592/2)pCuiv.Problems:-notveryselective-manycanonlybeusedatneutralpH