无机及分析化学第三版市公开课一等奖百校联赛优质课金奖名师赛课获奖课件.ppt

,单击此处编辑母版标题样式,单击此处编辑母版文本样式,第二级,第三级,第四级,第五级,*,本资料仅供参考，不能作为科学依据。谢谢。本资料仅供参考，不能作为科学依据。本资料仅供参考，不能作为科学依据。谢谢。本资料仅供参考，不能作为科学依据。,单击此处编辑母版标题样式,单击此处编辑母版文本样式,第二级,第三级,第四级,第五级,*,本资料仅供参考，不能作为科学依据。谢谢。本资料仅供参考，不能作为科学依据。本资料仅供参考，不能作为科学依据。谢谢。本资料仅供参考，不能作为科学依据。,第10.2章 络合平衡和络合滴定法,10.2.1 概述,10.2.2 络合平衡,10.2.3 络合滴定基本原理,10.2.4 络合滴定条件选择,10.5.5 络合滴定方式和应用,1/109,10.2.1 概述,以,络合反应,和,络合平衡,为基础滴定分析方法,金属离子,络合剂,2/109,lg,K,1,K,4,:,4.1、3.5、2.9、2.1,lg,K,总,=12.6,2+,Cu,2+,-NH,3,络合物,简单络合剂:,NH,3,Cl,-,CN,-,F,-,OH,-,3/109,螯合剂,乙二胺-Cu,2+,三乙撑四胺-Cu,2+,lg,K,1,=10.6,lg,K,2,=9.0,lg,K,总,=19.6,lg,K,=20.6,4/109,EDTA,乙二胺四乙酸,(H,4,Y),E,thylene,D,iamine,T,etra,A,cetic acid,乙二胺四乙酸二钠盐,(Na,2,H,2,Y),：,：,：,：,5/109,EDTA,H,6,Y,2,H,+,+H,5,Y,+,H,5,Y,H,+,+H,4,Y,H,4,Y H,+,+H,3,Y,-,H,3,Y,-,H,+,+H,2,Y,2-,H,2,Y,2-,H,+,+HY,3-,HY,3-,H,+,+Y,4-,K,a1,=,10,-0.90,H,+,H,5,Y,H,6,Y,K,a2,=,10,-1.60,H,+,H,5,Y,H,5,Y,K,a3,=,10,-2.00,H,+,H,3,Y,H,4,Y,K,a6,=,10,-10.26,H,+,HY,Y,K,a5,=,10,-6.16,H,+,HY,H,2,Y,K,a4,=,10,-2.67,H,+,H,2,Y,H,3,Y,6/109,EDTA:,-pH,图,H,6,Y,2+,H,5,Y,+,H,4,Y,H,3,Y,-,H,2,Y,2-,HY,3-,Y,4-,7/109,Ca-EDTA螯合物立体构型,EDTA 通常与金属离子形成,1:1,螯合物,多个,五元环,8/109,一些金属离子与,EDTA,形成常数,Hg,2+,21.8,Th,4+,23.2,Fe,3+,25.1,Bi,3+,27.9,ZrO,2+,29.9,Fe,2+,14.3,La,3+,15.4,Al,3+,16.1,Zn,2+,16.5,Cd,2+,16.5,Pb,2+,18.0,Cu,2+,18.8,Mg,2+,8.7,Ca,2+,10.7,Na,+,1.7,lg,K,lg,K,lg,K,lg,K,9/109,10.2.2,络合平衡(p181,5.5),1 络合物稳定常数,(,K,),M+Y=MY,K,MY,=,K,不稳,=,10/109,多配位金属络合物,11/109,络合物逐层稳定常数,K,i,K,表示,相邻,络合物之间关系,M+L=ML,ML+L=ML,2,ML,n-1,+L=ML,n,12/109,累积稳定常数,ML=,1,M L,ML,2,=,2,M L,2,ML,n,=,n,M L,n,13/109,溶液中各级络合物分布,ML=,1,M L,ML,2,=,2,M L,2,ML,n,=,n,M L,n,M+L=ML,ML+L=ML,2,ML,n-1,+L=ML,n,C,M,=M+ML+ML,2,+ML,n,=M(1+,1,L+,2,L,2,+,n,L,n,),14/109,溶液中各级络合物分布分数,M,=M/C,M,=,1/(,1+,1,L+,2,L,2,+,n,L,n,),ML,=ML/C,M,=,1,L,/(,1+,1,L+,2,L,2,+,n,L,n,),=,M,1,L,MLn,=ML,n,/C,M,=,n,L,n,/(,1+,1,L+,2,L,2,+,n,L,n,),=,M,n,L,n,15/109,酸可看成质子络合物,Y,4-,+H,+,HY,3-,HY,3-,+H,+,H,2,Y,2-,H,2,Y,2-,+,H,+,H,3,Y,-,H,3,Y,-,+H,+,H,4,Y,H,4,Y +H,+,H,5,Y,H,5,Y,+,+,H,+,H,6,Y,2,K,1,=,10,10.26,1,=,K,1,=,10,10.26,1,K,a6,K,2,=,10,6.16,2,=,K,1,K,2,=,10,16.42,1,K,a5,K,3,=,10,2.67,3,=,K,1,K,2,K,3,=,10,19.09,1,K,a4,K,4,=,10,2.00,4,=,K,1,K,2,K,3,K,4,=,10,21.09,1,K,a3,K,5,=,10,1.60,5,=,K,1,K,2,.,K,5,=,10,22.69,1,K,a2,K,6,=,10,0.90,6,=,K,1,K,2,.,K,6,=,10,23.59,1,K,a1,16/109,EDTA,相关常数,10,23.59,10,22.69,10,21.09,10,19.09,10,16.42,10,10.26,常数,6,5,4,3,2,1,累积,10,0.90,10,1.60,10,2.00,10,2.67,10,6.16,10,10.26,常数,K,6,K,5,K,4,K,3,K,2,K,1,逐层,10,-10.26,10,-6.16,10,-2.67,10,-2.00,10,-1.60,10,-0.90,常数,K,a6,K,a5,K,a4,K,a3,K,a2,K,a1,离解,17/109,2 络合反应副反应和,副反应系数（p184,5.5.2),M +Y =MY,(主反应),OH,-,MOH,M(OH),p,A,MA,MA,q,H,+,HY,H,6,Y,N,NY,H,+,OH,-,MHY,MOHY,副反应,18/109,副反应系数,19/109,（1）,滴定剂副反应系数,Y:,Y(H),Y(N),Y(H)：,酸效应系数,Y(N)：,共存离子效应系数,20/109,酸效应系数,1,(Y),21/109,例1 计算 pH5.00时EDTA,Y(H),解：,=1+10,-5.0010.26,+10,-10.00+16.42,+10,-15.00+19.09,+10,-20.0021.09,+10,-25.00+22.69,+10,-30.00+23.59,=1+10,5.26,+10,6.42,+10,4.09,+10,1.09,+10,-2.31,+10,-6.41,=10,-6.45,Y(H),lg 6.45,a,=,22/109,lg,Y(,H),pH图,lg,Y(H),EDTA酸效应系数曲线,lg,Y(H),可查表,23/109,共存离子效应系数,Y(N),=,=,Y,Y,Y+NY,Y,=1+K,NY,N,=,Y(H),+,Y(N),-1,Y,=,Y,Y,Y+HY+H,2,Y+NY,Y,24/109,（2）金属离子副反应系数,M,M(NH3),=,M(OH),=,1+OH,1,+OH,2,2,+-OH,n,n,可查表,1+NH,3,1,+NH,3,2,2,+NH,3,3,3,+NH,3,4,4,25/109,Al,Fe,III,Bi,Zn,Pb,Cd,Cu,Fe,II,lg,M(OH),pH,lg,M(OH),26/109,lg,M(NH3),lgNH,3,曲线,Cu,Ag,Ni,Zn,Cd,Co,lg,M(NH3),27/109,2个副反应同时存在时,M,=,M(A1),+,M(A2),+-,M(An),-(,n,-1),若有,n,个副反应,28/109,例2 用EDTA滴定Zn,2+,至化学计量点附近,pH=11.00，NH,3,=0.10molL,-1,计算,lg,Zn,查附录表,pH=11.00时,lg,Zn(OH),=5.4,lg,Zn,=,lg(,Zn(NH3),+,Zn(OH),-1,)=lg(10,5.1,+10,5.4,-1)=,10,5.6,Zn(NH3),=,1+NH,3,1,+NH,3,2,2,+NH,3,3,3,+NH,3,4,4,=1+10,-1.00+2.27,+10,-2.00+4.61,+10,-3.00+7.01,+10,-4.00+9.06,=1+10,1.27,+10,2.61,+10,4.01,+10,5.06,=,10,5.10,29/109,例3,用EDTA滴定Zn,2+,至化学计量点附近,pH=9.0，,c,(NH3),=0.10molL,-1,计算,lg,Zn(NH3),c,(NH3),=NH,3,+NH,4,+,+,忽略,Zn(NH3),=,1+NH,3,1,+NH,3,2,2,+NH,3,3,3,+NH,3,4,4,30/109,（3）络合物副反应系数,MY,M +Y=MY,H,+,OH,-,MHY M(OH)Y,强酸碱性溶,液中要考虑，,普通不考虑,酸性较强,MY(H),=1+K,MHY,H,+,碱性较强,MY(OH),=1+K,MOHY,OH,-,31/109,计算：pH=3.0、5.0时,lg,ZnY(H),K,ZnHY,=10,3.0,pH=3.0,ZnY(H),=1+10,-3.0+3.0,=2,lg,ZnY(H),=0.3,pH=5.0,ZnY(H),=1+10,-5.0+3.0,=1,lg,ZnY(H),=0,32/109,3 络合物条件(稳定)常数(p189,5.5.3),K,MY,=,K,MY,lg,K,MY,=lg,K,MY,-lg,M,-,lg,Y,+,lg,MY,普通来说：,lg,K,MY,=lg,K,MY,-lg,M,-,lg,Y,=,lg,K,MY,-lg,(,M(A1),+,M(A2),+-,M(An),-(,n,-1),-,lg,(,Y(H),+,Y(N),-1),33/109,例4,计算pH2.0和5.0时lg,K,ZnY,Zn +Y ZnY,Zn(OH),Y(H),ZnY(H),OH,-,H,+,H,+,lg,K,ZnY,=lg K,ZnY,-lg,Zn,-,lg,Y,+,lg,ZnY,lg K,ZnY,=16.5,lg K,ZnHY,=3.0,34/109,pH=2.0,lg,Y(H),=13.79,lg,Zn(OH),=0,ZnY(H),=1+H,K,ZnHY,=1+10,-2.0+3.0,=10,1.0,lg,ZnY(H),=1.00,lg,K,ZnY,=lg K,ZnY,-lg,Zn,-,lg,Y,+,lg,ZnY,=,16.50-0-13.79+1.00=3.71,35/109,pH=5.0,lg,Y(H),=6.45,lg,Zn(OH),=0,ZnY(H),=1+H,K,ZnHY,=1+10,-5.0+3.0,=1,lg,ZnY(H),=0.00,lg,K,ZnY,=lg K,ZnY,-lg,Zn,-,lg,Y,+,lg,ZnY,=,16.50-0-6.45+0=10.05,普通来说，可忽略,MY,36/109,lg,K,ZnY,pH曲线,lg,K,ZnY,lg,K,ZnY,lg,a,Zn(OH),lg,a,Y(H),lg,K,ZnY,lg,K,16.5,15,10,5,0,pH,0 2 4 6 8 10 12 14,37/109,0,2,4,6,8,14,10,12,pH,2,4,6,8,10,12,14,16,18,lg,K,MY,Cu,2+,Fe,3+,Hg,2+,Zn,2+,Mg,2+,Al,3+,lg,K,MY,pH曲线,lg,K,FeY,=25.1,lg,K,CuY,=18.8,lg,K,AlY,=16.1,38/109,例,计算pH9.0，,c,(NH3),=0.1molL,-1,时lg,K,ZnY,Zn +Y ZnY,NH,3,OH,-,H,+,Zn(NH,3,)Zn(OH)HY,lg,Y(H),=1.4,Zn,=,Zn(NH3),+,Zn(OH),-1=,10,3.2,+10,0.2,-1=10,3.2,lg,K,ZnY,=lg K,ZnY,-lg,Zn,-,lg,Y,=,16.50-3.2-1.4,=11.9,39/109,10.2.3 配位滴定基本原理(p398,10.2.2),1 配位滴定曲线,M +Y =MY,EDTA加入，M or M 不停减小，化学计量点时发生突跃,金属离子 M,C,M,V,M，,用C,Y,浓度Y滴定，体积为V,Y,40/109,MBE,M,+MY,=V,M,/(V,M,V,Y,)C,M,Y,+MY,=V,Y,/(V,M,V,Y,)C,Y,MY,=V,M,/(V,M,V,Y,)C,M,-M,=V,Y,/(V,M,V,Y,),C,Y,-,Y,K,MY,=,MY,M,Y,Y,=V,Y,/(V,M,V,Y,),C,Y,-V,M,/(V,M,V,Y,)C,M,-M,41/109,展开,K,MY,M,2,+K,MY,(C,Y,V,Y,-C,M,V,M,)/(V,M,+V,Y,)+1M,-,V,M,/(V,M,V,Y,),C,M,=0 ,滴定曲线方程,化学计量点（sp）时：C,Y,V,Y,-C,M,V,M,0,K,MY,M,sp,2,+M,sp,-C,M,sp,=0,M,sp,=,K,MY,=,M,V,Y,/(V,M,V,Y,),C,Y,-V,M,/(V,M,V,Y,)C,M,-M,V,M,/(V,M,V,Y,)C,M,-M,42/109,普通要求 log,K,MY,8，C,M,=0.01 mol/L,K,MY,C,M,sp,10,6,M,sp,=,pM,sp,=1/2(lg K,MY,+pC,M,sp,),43/109,普通要求 log,K,MY,8，C,M,=0.01 mol/L,K,MY,C,M,sp,10,6,c,M,越大，滴定曲线起点就越低，pM突跃就越大；反之，pM突跃就越小,。,值大小，是影响pM突跃主要原因之一，而,值取决于 ，和 值,值越大，值对应增大，pM突跃也大，反之就小,滴定体系酸度越大，pH越小，值越大，值越小，引发滴定曲线尾部平台下降，使pM突跃变小,44/109,10,-3,mol/L,10,-4,mol/L,10,-2,mol/L,K,=10,10,0,100,200,10,8,6,4,2,pM,滴定百分数,EDTA滴定不一样浓度金属离子,K,MY,一定，,c,(M)增大10倍，突跃范围增大一个单位。,pM,=3.0+p,c,sp,(M),45/109,200,100,0,2,4,6,8,10,pM,滴定百分数,K,=10,10,K,=10,8,K,=10,5,不一样稳定性络合体系滴定,浓度一定时，,K,MY,增大10倍，突跃范围增大一个单位。,c,=10,-2,mol L,-1,46/109,滴定突跃,sp前，0.1，,按剩下M,浓度计,sp后，+0.1，,按过量Y,浓度计,M,=0.1%,c,M,sp,即,：,pM,=3.0+p,c,M,sp,47/109,Zn +,Y ZnY,例,1.,用0.02molL,-1,EDTA滴定同浓度Zn,2，,若溶液pH为9.0，,c,(NH,3,)为0.2mol L,-1,。计算sp时pZn，pZn，pY,pY。,Zn(NH3),Zn(OH),Zn,OH,-,H,+,sp:pH9.0 c,Zn,sp,=0.01mol/L c(NH,3,)=,0.1 mol/L,48/109,pZn,sp,=pY,sp,=1/2(lg,K,ZnY,+p,c,Zn,sp,),=1/2(11.9+2.0)=7.0,lg,K,ZnY,=lg,K,ZnY,-,lg,Y,-,lg,Zn,=16.5-,1.4,-lg(,10,3.2,+10,0.2,-1,)=11.9,Zn=Zn,/,Zn,=10,-7.,/10,3.2,=10,-10.2,pZn,=10.2,pY,=pY,+lg,Y(H),=8.4,49/109,例2：pH=10 氨性buffer 中，NH,3,=0.2 mol/L,用0.02mol/L EDTA滴定0.02mol/L Cu,2+,计算 sp 时pCu,，若滴定是,0.02mol/L Mg,2+,sp 时pMg,又为多少？,sp:C,cu,sp,=,0.01 mol/L,NH,3,=,0.1 mol/L,Cu(NH3),=1+,1,NH,3,+,5,NH,3,5,=10,9.36,Cu(OH),=10,1.7,Cu,=,Cu(NH3),+,Cu(OH),-1=10,9.36,50/109,pH=10,lg,Y(H),=0.45,lg K,CuY,=lg K,CuY,-lg,Y(H),-,Cu,=18.80-0.45-9.36=8.99,pCu,=1/2(pC,Cu,sp,+,lg K,CuY,),=1/2(2.00+8.99)=5.50,51/109,对于Mg,2+,lg,Mg,=0,lg K,MgY,=lg K,MgY,-lg,Y(H),=8.70-0.45 =8.25,pMg,=1/2(pC,Mg,sp,+,lg K,MgY,),=1/2(2.00+8.25)=5.13,52/109,络合滴定法测定条件,考虑到浓度和条件常数对滴定突跃共同影响，用指示剂确定终点时，,若pM=0.2,要求,E,t,0.1%,则需lg,c,sp,K,MY,6.0,若,c,(M),sp,=0.010molL,-1,时,则要求,lg,K,8.0,53/109,一些浓度关系,c,(Y),Y,c,(Zn),Zn,c,(NH,3,),NH,3,54/109,2 金属指示剂(p400),金属指示剂作用原理,EDTA,HIn,+M,MIn,+M MY+,HIn,A色,B色,要求:A、B色不一样(适当pH)；,显色反应灵敏、快速、可逆性好；,稳定性适当，,K,MIn,K,MY,55/109,例,指示剂铬黑T,（EBT）,本身是酸碱物质,H,3,In,p,K,a1,H,2,In,-,p,K,a2,HIn,2-,p,K,a3,In,3-,紫红,3.9,紫 红,6.3,蓝,11.6,橙,pH,EBT使用pH范围：710,HIn,2-,蓝色,-,MIn,-,红色,56/109,惯用金属指示剂,PAN,(Cu-PAN),1-(2-吡啶偶氮)-2-萘酚,钙指示剂,磺基水杨酸(SSal),二甲酚橙(,XO,),(6元酸),铬黑T(,EBT,),指示剂,Cu,2+,(Co,2+,Ni,2+,),红,黄,2-12,Ca,2+,红,蓝,10-13,Fe,3+,紫红,无,2,Bi,3+,Pb,2+,Zn,2+,红,黄,K,MY,则封闭指示剂,Fe,3+,、Al,3+,、Cu,2+,、Co,2+,、Ni,2+,对,EBT、XO,有封闭作用；,若,K,MIn,太小，,终点提前,指示剂氧化变质现象,指示剂僵化现象,PAN,溶解度小,需加乙醇或加热,58/109,2 金属离子指示剂颜色转变点pM,t,计算,M+In=MIn,K,MIn,=,MIn,MIn,lg,K,MIn,=pM+lg,MIn,In,变色点：MIn=In,pM,t,=lg,K,MIn,=lg,K,MIn,-lg,In(H),In(H),=1+H,+,/K,a2,+H,+,2,/K,a1,K,a2,59/109,3 EDTA标准溶液配制与标定,Na,2,H,2,Y2H,2,O(乙二酸四乙酸二钠盐),1:直接配制,需基准试剂,用高纯水.,2:标定法,基准物质:Zn、Cu、Bi、CaCO,3,、MgSO,4,7H,2,O 等,水质量影响,：,1),Fe,3+,Al,3+,等封闭指示剂,难以确定终点;,2),Pb,2+,Zn,2+,Ca,2+,Mg,2+,等消耗滴定剂,影响准确度.,60/109,若配制EDTA溶液水中含有Pb,2+,Ca,2+,判断以下情况对测定结果影响.,1.以,CaCO,3,为基准物质标定EDTA,用以滴定试液中,Zn,2+,(Bi,3+,),XO,为指示剂.,pH10标定,Pb,2+,Ca,2+,与EDTA络合,pH5滴定Zn,2+,Ca,2+,不络合,c,(实际),c,(标定),c,(Zn,2+,)偏低.,pH1滴定Bi,3+,:,Pb,2+,Ca,2+,都不络合,c,(实际),c,(标定),c,(Bi)偏低.,61/109,2.以,Zn,2+,为基准物质,EBT,为指示剂,标定EDTA,用以测定试液中,Ca,2+,含量.,pH10标定,Pb,2+,Ca,2+,都络合,pH10滴定,Pb,2+,Ca,2+,都络合,c,(实际)=,c,(标定),c,(Ca)无影响,结论:标定与测定条件一致,对结果无影响.,62/109,10.2.4 络合滴定条件选择,1 络合滴定终点误差(p402,10.2.3),E,t,=,Y,ep-M,ep,C,M,sp,100,pM =pMep -pMsp,M,ep=,M,sp 10,-pM,Y,ep=,Y,sp 10,-pY,63/109,MYsp,M,sp,Y,sp,MYep,M,ep,Y,ep,=,MYsp,MYep,M,sp,M,ep,=,Y,ep,Y,sp,pM,=-pY,sp 时,M,sp,=,Y,sp,=,64/109,E,t,=,Y,sp 10,-pY,-,M,sp 10,-pM,C,M,sp,100,=,C,M,sp,（10,pM,-,10,-,pM,）,=,10,pM,-,10,-,pM,65/109,若pM=0.2,要求,E,t,0.1%,则需lg,C,M,sp,K,MY,6.0,普通,C,M,sp,=0.010molL,-1,时,则要求,lg,K,MY,8.0,66/109,例3：pH=10 氨性buffer 中，以EBT 为指示剂,用0.02mol/L EDTA滴定0.02mol/L Ca,2+,计算 TE%,，若滴定是,0.02mol/L Mg,2+,Et,又为多少？(已知,pH=10.0时，lg,Y(H),=0.45,lg,K,CaY,=10.69，lg,K,MgY,=8.70；EBT:,K,a1,=10,-6.3,K,a2,=10,-11.6,lg,K,Ca-EBT,=5.4，lg,K,Mg-EBT,=7.0,),解：lg,K,CaY,=lg,K,CaY,-lg,Y(H),=10.24,pCa,sp,=1/2(lg,K,CaY,+pC,Ca,sp,)=1/2(10.24+2)=6.10,EBT:,EBT(H),=,1+H,+,/K,a2,+H,+2,/,K,a2,K,a1,=40,lg,EBT(H),=1.6,67/109,pCa,ep,=,lg,K,Ca-EBT,=lg,K,Ca-EBT,-,lg,EBT(H),=5.4-1.6=3.8,pCa=,pCa,ep,-,pCa,sp,=3.8-6.1=-2.3,E,t,=,100,=-1.5%,10,-2.3,-,10,2.3,68/109,lg,K,MgY,=lg,K,MgY,-lg,Y(H),=8.7-0.45=8.25,pMg,sp,=1/2(lg,K,MgY,+pC,Ca,sp,)=1/2(8.25+2)=5.10,pMg,ep,=,lg,K,Mg-EBT,=lg,K,Mg-EBT,-,lg,EBT(H),=7.0-1.6=5.4,pMg=,pMg,ep,-,pMg,sp,=5.4-5.1=0.3,E,t=,100,=0.11%,10,0.3,-,10,-0.3,69/109,2 配位滴定中酸度控制(p404，10.2.4),H,4,Y,中Y,4-,反应，一直产生H,+,lg,Y(H),金属离子与OH,-,反应生成沉淀,指示剂需要一定pH值,酸碱 buffer,70/109,（1）单一金属离子滴定适宜pH范围,A.最高允许酸度,(,pH低限),比如:,K,(,BiY,)=27.9 lg,Y(H),19.9,pH0.7,K,(,MgY,)=8.7 lg,Y(H),0.7,pH9.7,K,(,ZnY,)=16.5 lg,Y(H),8.5,pH4.0,(不考虑,M,),lg,K,(MY)=lg,K,(MY)-lg,Y,(H),8,有,lg,Y,(H),lg,K,(MY),-,8,对应pH即为pH,低,若pM=0.2,要求,TE,0.1%,则lg,c,sp,K,(MY)6,若,c,sp,=0.01molL,-1,，,则,lg,K,(MY)8,71/109,B.最低酸度,(pH高限),以不生成氢氧化物沉淀为限,对 M(OH),n,(,I,=0.1,),c,(M)(初始),例,K,sp,(Zn(OH),2,)=10,-15.3,即 pH7.2,?,可在pH10氨性缓冲液中用Zn,2+,标定EDTA,72/109,C.最正确酸度,金属指示剂也有酸效应，与pH相关,pM,t,pM,sp,时pH,P112 例14,73/109,D.酸度控制,M+H,2,Y=MY+2H,+,需加入缓冲剂控制溶液pH,缓冲溶液选择与配制:,适当缓冲pH范围:pHp,K,a,足够缓冲能力:浓度计算,不干扰金属离子测定:,例 pH5,滴定Pb,2+,六次甲基四胺缓冲,pH10,滴定Zn,2+,c,(NH,3,)不能太大,74/109,3 混合金属离子选择性滴定p406,10.2.5,M +Y =MY,K,MY,K,NY,K,MY,=,K,MY,/,Y,Y,=,Y(H),Y(N),1,Y(N),=1+N,K,NY,c,(N),K,NY,H,+,H,i,Y,N,NY,Y(N),Y(H),(1)控制酸度分步滴定,M+N,75/109,M、N共存时,lg,K,MY,与,pH,关系,(a),(b),lg,a,Y(H),lg,a,Y,lg,a,Y(N),lg,a,pH,pH,lg,K,MY,lg,K,MY,76/109,K,MY,=,K,MY,/,Y,Y,=,Y(H),Y(N),1,Y(H),Y(N),时,，,Y,Y(H),（相当于N不存在）,Y(H),5,能,(2)滴定酸度范围:,Y(H),=,Y(Ca),=10,8.7,pH,低,=4.0,pH,高,=7.0,79/109,例：,Pb,+2,-Bi,+3,合金中Bi,3+,、Pb,2+,连续测定,lg,K,(BiY)=27.9,lg,K,(PbY)=18.0,lgK,=9.9,5,能够滴定Bi,3+,Y(Pb),1+10,-2.0+18.0,=10,16.0,lg,Y(H),lg,Y(Pb),=16.0时,pH=1.4,Bi,3+,水解,影响滴定,在pH1.0条件下滴定Bi,3+,(XO),lg,Y(H),18.3 lg,K,(BiY)=27.9-18.3=9.6,能够准确滴定,滴定,Bi,3+,后,用N,4,(CH,2,),6,调pH至5左右,继续滴定Pb,2+,80/109,例4：,0.02mol/L EDTA滴定0.02mol/L Zn,2+,和 0.1 mol/L Mg,2+,混合溶液，能否准确滴定？,(已知,pH=5.5时，lg,Y(H),=5.51,lgK,ZnY,=16.5,lgK,CaY,=10.69，lgK,MgY,=8.70；lgK,ZnIn,=5.7,),若溶液中共存离子不是Mg,2+,而是 0.1 mol/L Ca,2+,能否准确滴定Zn,2+,？,若在pH=5.5时，以XO 为指示剂,进行滴定，发觉Ca,2+,有干扰，而Mg,2+,无干扰，为何？,能否不分离也不加掩蔽剂来消除Ca,2+,干扰，已知XO与Ca,2+,、Mg,2+,均不显色。,81/109,lg(,K,zny,C,Zn,sp,)lg(,K,Mgy,C,Mg,sp,),=lg(10,16.5,0.02/2,)lg(10,8.7,0.1/2,),=,7.1,6,Et,0.1%，,Mg,2+,无干扰,lg(,K,zny,C,Zn,sp,)lg(,K,Cay,C,Ca,sp,),=lg(10,16.5,0.02/2,)lg(10,10.7,0.1/2,),=,5.1,5,E,t,0.3%，,Ca,2+,无干扰,82/109,pH=5.5时，lg,K,ZnIn,=5.7,pZn,ep,=5.7,Zn,2+,，Mg,2+,lg,K,ZnY,=lg,K,ZnY,lg(,K,Mgy,C,Mg,sp,),Y(H),？,=16.5-8.7+1.3,=9.1,pZn,sp,=1/2(9.1+2)=5.55,pZn=0.15,E,t=0.02%,Mg,2+,不干扰,83/109,Zn,2+,，Ca,2+,lg,K,ZnY,=lg,K,ZnY,lg(,K,CaY,C,Ca,sp,),Y(H),？,=16.5-10.7+1.3,=7.1,pZn,sp,=1/2(7.1+2)=4.55,pZn=1.15,E,t=4%,Ca,2+,干扰,因为指示剂酸效应系数太小，,pZn 太大，酸度不适当,pH=5.0 时，lg,K,ZnIn,=4.8,pZn,ep,=4.8,pZn=0.25，Et=0.3%,不干扰,84/109,(2)使用掩蔽剂选择性滴定,(lg,K,Y(H),时,lg,K,MY,=lg,K,MY,-,lg,Y(N),M +Y =MY,H,+,H,i,Y,N,NY,H,k,A,A,NA,j,H,+,Y(N),1N,K,NY,Y(H),Y(N),时 lg,K,MY,=lg,K,MY,-,lg,Y(H),相当于N影响不存在,说明掩蔽效果好,86/109,待测溶液中浓度均为0.02mol/L Zn,2+,、Al,3+,，能否经过控制酸度选择性滴定Zn,2+,？若加入NH,4,F，使,F,-,=0.2 mol/L,调整pH=5.5，,用0.02molL,-1,EDTA滴定，XO 为指示剂，Et%为多少？,lg(K,zny,C,Zn,sp,)lg(K,Aly,C,Al,sp,),=lg(10,16.5,0.02/2,)lg(10,16.3,0.02/2,),=,0.2,5,不能选择滴定Zn,2+,87/109,加入F,-,以后,Al(F,),=,1+F,-,+F,-,2,2,+F,-,6,6,=10,16.20,Al=Al,/,Al(F,),=,C,Al,sp,/,Al(F,),=10,-18.20,Y(Al,),=1+Al,K,(AlY)=1+10,-18.20+16.1,=1,掩蔽效果好,Al无影响,Y,(H,),Y(Al,),Al,(,F,),Zn +Y =ZnY,H,+,Al,F,j,H,i,Y,AlY,Al,F,-,H,+,p,K,a,(HF)=3.1,F,(H,),=1,88/109,pH=5.5 时，lg,Y(H,),=5.51,lg,K,ZnY,=lg,K,ZnY,lg,Y(H,),=10.99,pZn,sp,=1/2(10.99+2)=6.50,pZn,t,=lg,K,ZnIn,lg,HIn,(H),=5.70,pZn=-0.80,TE=-0.02%,89/109,例,EDTA Zn,2+,+Cd,2+,lg,K,(ZnY)=16.5 lg,K,(CdY)=16.4,pH=5.5时,lg,Y(H),=5.7,c,(Zn)=,c,(Cd)=0.02,molL,-1,I,-,ep,=0.5,molL,-1,Zn +Y =ZnY,H,i,Y,Cd,CdY,I,-,CdI,j,H,+,Y(H,),Y(Cd,),Cd,（,I,）,90/109,I,-,Cd(I),Cd,0.5,molL,-1,10,5.1,10,7.1,10,9.4,10,5.7,1,-,4,c,(Cd),K,(CdY),Y(Cd),Y(H),改用,HEDTA,lg,K,ZnX,=14.5,lg,K,CdX,=13.0,X,(Cd),=1+10,-7.1,10,13.0,=10,5.9,lg,K,ZnX,=,14.5-5.9,=8.6 8,能够准确滴定.,使用掩蔽剂+选择滴定剂,lg,K,ZnY,=lg,K,ZnY,-,lg,Y(Cd),=16.5-9.4=,7.1,(,4;CN,-,pH10),2.不干扰待测离子:,如pH10测定Ca,2+,、Mg,2+,用F,-,掩蔽Al,3+,，则CaF,2,、MgF,2,CN,-,掩蔽Cu,2+,Co,2+,Ni,2+,Zn,2+,Cd,2+,F,-,掩蔽Al,3+,;,三乙醇胺,Al,3+,Fe,3+,92/109,B.氧化还原掩蔽法,FeY,lg,K,BiY,=27.9,lg,K,HgY,=21.8,lg,K,FeY,-,=25.1,lg,K,FeY,2-,=14.3,红,黄,抗坏血酸(Vc),或NH,2,OH,HCl,红,黄,pH=1.0,XO,EDTA,EDTA,pH5-6,测Fe,测Bi,Bi,3+,Fe,3+,Bi,3+,Fe,2+,BiY,Fe,2+,93/109,C.沉淀掩蔽法,Ca,2+,OH,Ca,2+,Y,CaY,Mg,2+,pH12,Mg(OH),2,Ca指示剂,Mg(OH),2,测Ca,EBT,？,lg,K,CaY,=10.7,lg,K,MgY,=8.7,p,K,sp,:Ca(OH),2,=4.9,Mg(OH),2,=10.4,另取一份，在pH10测总量,94/109,4.用其它氨羧络合剂滴定,95/109,10.2.6 络合滴定方式及应用p409,1.,直接滴定法:,方便，准确,例,水硬度测定:,Ca,2+,、Mg,2+,lg,K,CaY,=10.7 lg,K,Ca-EBT,=5.4,lg,K,MgY,=8.7 lg,K,Mg-EBT,=7.0,在,pH=10,氨性缓冲溶液中，EBT为指示剂，测Ca,2+,、Mg,2+,总量,；,pH12,，Mg(OH),2,用,钙指示剂,测,Ca,2+,量,例,Bi,3+,、Pb,2+,连续滴定,96/109,2.,返滴定法:,被测M与Y反应慢，易水解，封闭指示剂。,例,Al,3+,测定,Al,3+,AlY+Y,(剩),AlY,ZnY,pH34,Y(过)，,pH56,冷却,XO,Zn,2+,lg,K,=16.5,lg,K=,16.1,黄,红,97/109,3.,间接滴定法,测非金属离子:PO,4,3-,、,SO,4,2-,待测M与Y络合物不稳定:K,+,、Na,+,MgY+Y,(剩),Mg,2+,NH,4,+,H,+,溶,Y(过),？,pH10,溶解,Y,K,+,Mg,2+,PO,4,3-,MgNH,4,PO,4,K,2,NaCo(NO,2,),6,6H,2,O,CoY,Mg,2+,98/109,4.,置换法:,被测M与Y络合物不稳定,例,lg,K,AgY,=7.3 lg,K,NiY,=18.6,XO?,EBT？,2Ag,+,+Ni(CN),4,2-,2Ag(CN),2,-,+Ni,2+,pH=10,氨 缓,Y,紫脲酸铵,MgY,+EBT,+Ca,2+,CaY+,MgEBT,+Ca,2+,例,间接金属指示剂,Y,CaY+,MgY,+EBT,99/109,置换出EDTA,Al,3+,Pb,2+,AlY,PbY+Y(剩),AlY,PbY,ZnY,AlF,6,3-,PbY+Y,(析出),ZnY,AlF,6,3-,PbY,ZnY,pH34,Y(过),Zn,2+,F,-,Zn,2+,(测Al),(,测Al,Pb总量,),pH56,冷却,XO,黄红,冷却,黄红,100/109,设计方案,Zn,2+,Mg,2+,分别测定,1.控制酸度,Zn,2+,Mg,2+,ZnY,MgY,Y,pH10,EBT,另取一份：,红蓝,c,总,-,c,(Zn)=,c,(Mg),Y,Zn,2+,Mg,2+,ZnY,Mg,2+,红黄,pH5.5,XO,测,c,(Zn),101/109,2.络合掩蔽法,另取一份测总量,方法同上,Zn,Mg,EBT,pH10,KCN,Zn(CN),4,2-,MgY,Y,红黄,102