北京大学分析化学04络合

PartIVComplexationReactionsandTitration4.1Introduction4.2ComplexationEquilibria4.3PrincipleforComplexationTitration4.4SelectiveTitration4.5ApplicationofComplexationTitrationWhatAreWeGoingtoLearninThisChapter?zTheformsandreactionsthatametalionmaytakezThe“realreal”formationconstantofcomplexationConditionalConstantConditionalConstantSidereactioncoefficientSidereactioncoefficient--AnalternativeapproachtotacklechemicalAnalternativeapproachtotacklechemicalequilibriaequilibriazComplexationtitrationcurve,Metallochromeindicator,andestimationoftitrationerrorszSelectivelytitrationofonetypemetalioninamixtureofseveraltypesofmetalionszWaysofcomplexationtitrationandapplicationRecommendedReferenceBooks•AndersRingbom.ComplexationinAnalyticalChemistry-AGuidefortheCriticalSelectionofAnalyticalMethodsBasedonComplexationReactions.InterSciencePublishers,aDivisionofJohnWiley&Sons,1963.•A.林邦著，戴明译，杨麒校.分析化学中的络合作用.高等教育出版社,1987.4.1Introduction–InorganicLigandsNH3:Cu2+,Co2+,Ni2+,Zn2+,Ag+,Cd2+CN－:Cu2+,Co2+,Ni2+,Zn2+,Ag+,Cd2+,Hg2+,Fe2+,Fe2+OH－:Cu2+,Co2+,Ni2+,Zn2+,Ag+,Cd2+,Fe2+,Fe3+,Bi3+,Al3+F－:Al3+,Fe3+Cl－:Ag+,Hg2+NotstableenoughforapplicationoftitrimetryButusefulformaskingpurposeComplexesStoichiometryNo.HeterocyclicRingsFormationConstant1:40lgβ4=12.61:22lgβ2=19.61:13lgK=20.6CH2CH2H2NNH2CuH2CH2CH2NNH2CH2CH2H2NNHCuH2CH2CH2NNHH2CCH2CuNH3NH3H3NH3NRelationbetweenFormationConstantandtheNumberofHeterocyclicRingsWhyEDTA?乙二胺四乙酸(H4Y)EthyleneDiamineTetraAceticacid乙二胺四乙酸二钠盐(Na2H2Y·2H2O)HOOCH2C-OOCH2CCH2COO-CH2COOHNH+-CH2-CH2-NH+Ca-EDTAComplexOCaOONONCOH2CH2CCH2CH2CCCH2CH2COOOEDTADistributionDiagram0.00.20.40.60.81.002468101214pHxH6Y2+H5Y+H4YH3Y-H2Y2-HY3-Y4-FormationConstantforM-EDTAlgKlgKlgKlgKNa+1.7Mg2+8.7Ca2+10.7Fe2+14.3La3+15.4Al3+16.1Zn2+16.5Cd2+16.5Pb2+18.0Cu2+18.8Hg2+21.8Th4+23.2Fe3+25.1Bi3+27.9ZrO2+29.94.2ComplexationEquilibria4.2.1StabilityConstant(K,β)andDistributionCoefficients(x0～xn)instabilitydissM+Y=MY[MY][M][Y]1()KKKK==StepwiseStabilityKi=1[ML][M][L]K=-1[ML][ML][L]nnnK=22[ML][ML][L]K●●●diss11nK=Kdiss121−=nKK11=nKKdiss●●●●●●K–definetherelationbetweentwocomplexeswithadjacentnumberofligandsM+L=MLML+L=ML2MLn-1+L=MLnComplexes2+2+331Cu+NH=Cu(NH)K2+2+33322Cu(NH)+NH=Cu(NH)KK2+2+323333Cu(NH)+NH=Cu(NH)K2+2+333344Cu(NH)+NH=Cu(NH)Predominance-areaDiagrampL=lgK1[M]=[ML]pL=lgK2[ML]=[ML2]pL=lgK3[ML2]=[ML3]pL=lgK4[ML3]=[ML4]Cu2+Cu(NH3)2+Cu(NH3)22+Cu(NH3)32+Cu(NH3)42+lgK1lgK2lgK3lgK44.13.52.92.1pL3-+ConsideringPOwithHasligand,whatwouldyouget?4StepwisestabilityconstantnotcumulativeconstantCumulativeConstantβ(1)==11[ML][M][L]KβM+L=ML1=i22222[ML][ML][ML][M][L][ML][L][M][L]KKβ==M+2L=ML2●●●β==12[ML][M][L]nnnnKKKM+nL=MLnCumulativeConstantβ(2)[ML]=[M][L]β1[ML2]=[M][L]2β2[MLn]=[M][L]nβn●●●DistributionCoefficientsofComplexes0[M]=[M]+[ML][M]=+[(ML])Mnxcβββ212[M]=[M](1+[L]+[L]++[L])nnβββ2121=1+[L]+[L]++[L]nnDistributionCoefficientsofComplexes11212[L]=1+[L][ML]=(M)+[L]++[L]nnxcββββ⋅⋅⋅●●●=1[L][ML]==(M)1+[L]nnnnniiixcββ∑2222122[L]=1+[L]+[L[ML]=(]++[)]MLnnxcββββ⋅⋅⋅xvariesonlywhen[L]changesDistributionDiagramforCu-MH3Complexes00.510246p[NH3]xCu2+Cu(NH3)2+Cu(NH3)22+Cu(NH3)42+Cu(NH3)32+DistributionDiagramofHg-ClComplexationSideReactionCoefficientM+Y=MYM′Y′MY′（）[(MY)](MY)=[M][Y]K′′′′ConditionalFormationConstantOH-MOH●●●M(OH)pAMA●●●MAqH+HY●●●H6YNNYH+OH-MHYMOHYH+4.2.2SideReactionCoefficients[M′]:ConcentrationoffreemetalionplusallthemetalinsolutionthathasnotreactedwithY未与Y反应的所有含M形式的浓度之和[Y′]:ConcentrationoffreeligandplusallspeciesofthecomplexingagentnotboundtoM未与M反应的所有含Y形式的浓度之和[(MY)′]:SumofconcentrationsofallspeciescontainingMandLinthemolarration1:1滴定产物所有形式浓度之和Y[Y][Y]α′=Zn[Zn][Zn]α′=ZnY[(ZnY)][ZnY]α′=Example:ThefollowingreactionsmayoccurduringtitrationofZn2+usingEDTAinthepresenceofCa2+andNH3.MYMY[(MY)](MY)==(MY)[M][Y]KKααα′′⋅′′SideReactionCoefficients[(MY)](MY)=[M][Y]KSideReactionCoefficients+243)Zn(NH−24Zn(OH)H+…H+HY●●●Ca2+CaYαY(H)αY(Ca)Y[Y][Y]α′=Zn[Zn][Zn]α′=Zn+Y=ZnYOH-Zn(OH)+●●●NH3Zn(NH3)2+●●●αZn(OH)H6YH+OH-ZnHYZnOHYαZnY(H)αZnY(OH)ZnY[(ZnY)][ZnY]α′=3Zn(NH)αWhenThereAreMoreThan2SideReactionsPresent22M[M]+[MOH]+M(OH)]+++=[[MA]+[MMA]]α⋅⋅⋅⋅⋅⋅22[M[M]+[MOH]+M(OH)]+++[MA]+[+-=[MA]M]][M]⋅⋅⋅⋅⋅⋅M(OH)M(A)=+-1ααFornsidereactions：αM=αM(A1)+αM(A2)+…+αM(An)-(n-1)SideReactionCoefficientsforEDTA26Y(H)[Y'][Y][HY][HY][HY][Y][Y]α⋅⋅⋅++++==26126[Y][Y][H][Y][H][Y][H][Y]βββ++++++⋅⋅⋅+=261261[H][H][H]βββ+++=+++⋅⋅⋅+Y(H)]Y'[]Y[α=α=⋅Y(H)[Y'][Y]1Y(H)≥αSideReactionCoefficientsforEDTAProcedureforcalculatinglogαY(H)KaiKiHβiHαY(H)logαY(H)pHSortbackwardsandcalculateforwardsExample1：CalculateαY(H)atpH=5.00βββαY(H)+++26126=1+[H]+[H]++[H]-5.00+10.34-10.00+16.58-15.00+19.33=1+10+10+10-20.00+21.40-25.00+23.0-30.00+23.9+10+10+105.346.584.331.40-2.0-6.16.60=1+10+10+10+10+10+10=10Y(H)log6.60α=logαY(H)asaFunctionofpH04812162024024681012pHLogαY(H)SideReactionCoefficientsforMetalIonsαM(NH3)=1+[NH3]β1+[NH3]2β2+[NH3]3β3+[NH3]4β4αM(OH)=1+[OH]β1+[OH]2β2+…+[OH]nβnlogαM(OH)–教程p743logαM(NH3)vs.log[NH3]forSelectedMetalIons02468101214-3-2-10log[NH3]CuAgNiZnCdCologαM(NH3)lgαM(OH)vs.pHforSelectedMetalIon02468101214161802468101