络合滴定法.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,*,*,第,6,章 络合滴定法,Complex titration,6.1,分析化学中常用的络合物,6.2,络合物的平衡常数,6.3,副反应系数和条件稳定常数,6.4,络合滴定法的基本原理,6.5,准确滴定与分别滴定判别式,6.6,络合滴定中酸度的控制,6.7,提高络合滴定选择性的途径,6.8,络合滴定方式及应用,6.1,分析化学中常用的络合物,以,络合反应,和,络合平衡,为基础的滴定分析方法,一,.,简单络合物,:,由中心离子和单齿配体组成,NH,3,Cl,-,F,-,Cu,2+,-NH,3,络合物,lg,K,1,K,4,:,4.1,、,3.5,、,2.9,、,2.1,lg,K,总,=12.6,3,常用,无机络合剂,NH,3,:,Cu,2+,、,Co,2+,、,Ni,2+,、,Zn,2+,、,Ag,+,、,Cd,2+,CN,:,Cu,2+,、,Co,2+,、,Ni,2+,、,Zn,2+,、,Ag,+,、,Cd,2+,、,Hg,2+,、,Fe,2+,、,Fe,3+,OH,:,Cu,2+,、,Co,2+,、,Ni,2+,、,Zn,2+,、,Ag,+,、,Cd,2+,、,Fe,2+,、,Fe,3+,、,Bi,3+,、,Al,3+,F,:,Al,3+,、,Fe,3+,Cl,:,Ag,+,、,Hg,2+,逐级形成，不稳定，常用做掩蔽剂,.,二,.,螯合物,(chelates),:,乙二胺，,EDTA,等,乙二胺,-Cu,2+,螯合物主要类型,1.“OO”,型,2.“NN”,型,乙二胺,-Cu,2+,三乙撑四胺,-Cu,2+,3.“NN,”,型,lg,K,1,=10.6,lg,K,2,=9.0,lg,K,总,=19.6,lg,K,=20.6,4.“NO”,型,氨羧络合剂,乙二胺四乙酸,EDTA,Ethylene diamine tetraacetic acid,乙二胺四乙酸,(H,4,Y),乙二胺四乙酸二钠盐,(Na,2,H,2,Y),：,：,：,：,乙二胺四丙酸,(EDTP),Ethylene diamine tetrapropyl acid,乙二胺二乙醚四乙酸,(EGTA),Ethylene glyceroldiamine tetraacetic acid,环已烷二胺四乙酸,(,CyDTA),Cyclohexane diamine tetraacetic acid,5.,含,S,型,三,.,乙二胺四乙酸,EDTA,特点,:,1),反应速度快。,2),反应彻底,一步完成,(1:1),无分级络合现象,3),水中溶解度小，难溶于酸和有机溶剂；易溶于,NaOH,或,NH,3,溶液,Na,2,H,2,Y2H,2,O,4),生成的络合物易溶于水,H,6,Y,2+,H,5,Y,+,H,4,Y,H,3,Y,-,H,2,Y,2-,HY,3-,Y,4-,各型体浓度取决于溶液,pH,值,pH,1,强酸性溶液,H,6,Y,2+,pH 2.67,6.16,主要,H,2,Y,2-,pH,10.26,碱性溶液,Y,4-,四,.EDTA,的螯合物,EDTA,通常与金属离子形成,1:1,的螯合物,多个,五元环,1),广泛配位性,五元环螯合物稳定、完全、迅速,2),具,6,个配位原子，与金属离子,多形成,1,：,1,配合物,3),与无色金属离子形成的螯合物无色，利于指示,终点；与有色金属离子形成的螯合物颜色更深,EDTA,螯合物特点：,一,.,络合物的稳定常数,(,K,稳,),6.2,络合物的平衡常数,MY,MY,K,MY,=,M +Y =MY,讨论,：,K,MY,越,大，配合物稳定性越高，配合反应完全,某些金属离子与,EDTA,的形成常数,Hg,2+,21.8,Th,4+,23.2,Fe,3+,25.1,Bi,3+,27.9,Fe,2+,14.3,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,逐级稳定常数,K,i,K,表示,相邻,络合物之间的关系,M+L=ML,ML+L=ML,2,ML,n-1,+L=ML,n,累积稳定常数,表示络合物与,配体,之间的关系,ML,ML,K,1,=,ML,2,MLL,K,2,=,ML,n,ML,n-1,L,K,n,=,ML,ML,1,=,K,1,=,ML,2,ML,2,2,=,K,1,K,2,=,ML,n,ML,n,n,=,K,1,K,2,K,n,=,逐级稳定常数,K,与累积稳定常数,二,.,溶液中各级络合物的分布,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,),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,只是,L,的函数，与分析浓度,c,无关。,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,图,三,.,平均配位数,表示金属离子络合配体的平均数。,M +Y =MY,主反应,副反应,OH,-,L,H,+,N,H,+,OH,-,MOH,MHY,MOHY,NY,HY,M(OH),n,ML,ML,n,H,6,Y,M,Y,M,Y,6.3,副反应系数和条件稳定常数,副反应系数,:,未参加主反应组分的浓度,X,与平衡浓度,X,的比值，用,表示。,M,a,M,=,M,Y,a,Y,=,Y,MY,a,MY,=,MT,一,.,副反应系数,side reaction coefficient,M +Y =MY,主反应,副反应,OH,-,L,H,+,N,H,+,OH,-,MOH,MHY,MOHY,NY,HY,M(OH),n,ML,ML,n,H,6,Y,M,Y,M,Y,1.,络合剂,Y,的副反应及副反应系数,Y:,Y(H),：,酸效应系数,Y(N),：,共存离子效应系数,Y,a,Y,=,Y,H,+,N,NY,HY,H,6,Y,Y,M +Y =MY,1,Y,1,）酸效应系数,Y(H),：,Y,a,Y(H),=,=,=,Y,=(1+,1,H,+,+,2,H,+,2,+,6,H,+,6,),Y,Y+HY+H,2,Y+H,6,Y,Y,Y+YH,+,1,+YH,+,2,2,+YH,+,6,6,=,a,Y(H),1,Y,a,Y(H),Y,=,2,）共存离子效应系数,Y(N),Y,a,Y(N),=,=,=1+,K,NY,N,Y,Y,Y+NY,Y,a,Y(N),=,=,=1+,K,N,1,Y,N,1,+,K,N,2,Y,N,2,+,K,N,n,Y,N,n,=,a,Y(N1),+,a,Y(N2),+,a,Y(Nn),-(n-1),Y,Y,Y+N,1,Y+N,2,Y+N,n,Y,多种共存离子,3,）,Y,的总副反应系数,Y,=,Y(H),+,Y(N),-1,Y,=,=,Y+HY+H,2,Y+NY,Y,Y,Y,2.,金属,离子,M,的副反应及副反应系数,M,M(OH),=,1+,1,OH,-,+,2,OH,-,2,+,n,OH,-,n,M(L),=,1+,1,L,+,2,L,2,+,n,L,n,M +Y=MY,OH,-,L,MOH,M(OH),n,ML,ML,n,M,多种络合剂共存,M(L),=,1+,1,L,+,2,L,2,+,n,L,n,M,=,M(L1),+,M(L2),+,M(Ln),-(,n,-1),Al,Fe,III,Bi,Zn,Pb,Cd,Cu,Fe,II,lg,M(OH),pH,3.,络合物的副反应系数,MY,酸性较强,MY(H),=1+,K,MHY,H,+,碱性较强,MY(OH),=1+,K,M(OH)Y,OH,-,M +Y=MY,H,+,OH,-,MHY,MOHY,MY,计算：,pH=3.0,、,5.0,时的,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,lg,K,MY,=lg,K,MY,-lg,M,-,lg,Y,+,lg,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),K,MY,=,K,MY,MY,M,Y,a,MY,a,M,a,Y,二,.,条件稳定常数,conditional stability constant,K,MY,lg,K,ZnY,pH,曲线,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+,K,MY,=,MY,MY,三,.,金属离子缓冲溶液,pM =lg,K,MY,+,lg,Y,MY,pL =lg,K,ML,+,lg,M,ML,6.4,络合滴定基本原理,一,.,络合滴定曲线：,溶液,pM,随滴定分数,(,a,),变化的曲线,M +Y =MY,EDTA,加入，金属离子被络合，,M or M,不断减小，化学计量点时发生突跃,MBE,M,+MY,=V,M,/(V,M,V,Y,)c,M,Y,+MY,=V,Y,/(V,M,V,Y,)c,Y,K,MY,=,MY,M,Y,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,sp,时：,c,Y,V,Y,-c,M,V,M,0,pM,sp,=1/2(lg,K,MY,+pc,M,sp,),K,MY,C,M,sp,10,6,金属离子,M,c,M,V,M,，,用,c,Y,浓度的,Y,滴定，体积为,V,Y,MY,=V,M,/(V,M,+V,Y,)c,M,-M,=V,Y,/(V,M,+V,Y,),c,Y,-,Y,Y,=V,Y,/(V,M,V,Y,),c,Y,-V,M,/(V,M,V,Y,)c,M,-M,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,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,sp,：,C,Y,V,Y,-C,M,V,M,0,K,MY,M,sp,2,+M,sp,-C,M,sp,=0,M,sp,=,-1,1+4,K,MY,c,M,sp,2,K,MY,一般要求,log,K,MY,8,，,c,M,=0.01 mol/L,K,MY,C,M,sp,10,6,pM,sp,=1/2(lg,K,MY,+pc,M,sp,),M,sp,=,-1,1+4,K,MY,c,M,sp,2,K,MY,滴定突跃,sp,前，,-0.1,，按剩余,M,浓度计算,sp,后，,+0.1,，按过量,Y,浓度计算,M,=0.1%,c,M,sp,即,：,pM,=3.0+p,c,M,sp,Y,=0.1%,c,M,sp,M,=,MY,K,MY,Y,MY,c,M,sp,pM,=lg,K,MY,-3.0,例：,pH=10,的氨性,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,，若滴定的是,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,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,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,浓度,:,增大,10,倍，突跃增加,1,个,pH,单位（下限）,K,MY,:,增大,10,倍，突跃增加,1,个,pH,单位（上限）,影响滴定突跃的因素,滴定突跃,pM,：,p,c,M,sp,+3.0,lg,K,MY,-3.0,络合滴定准确滴定条件：,lg,c,M,sp,K,MY,6.0,对于,0.0100molL,-1,的,M,lg,K,MY,8,才能准确滴定,HIn,+M,MIn,+M MY+,HIn,色,甲 色,乙 色,甲,要求,:,指示剂与显色络合物颜色不同,(,合适的,pH),；,显色反应灵敏、迅速、变色可逆性好；,稳定性适当，,K,MIn,K,MY,二,.,金属离子指示剂,1.,指示剂的作用原理,EDTA,（,Y,）,1,）金属离子指示剂变色点,pM,ep,的计算,M+In=MIn,K,MIn,=,MIn,MIn,lg,K,MIn,=pM+lg,MIn,In,变色点：,MIn=In,故,pM,ep,=lg,K,MIn,=lg,K,MIn,-lg,In(H),In(H),=1+H,+,/,K,a2,+H,+,2,/,K,a1,K,a2,2.,金属离子指示剂的选择,2,）常用,金属离子指示剂,指示剂,pH,范围,颜色变化,直接滴定离子,In,MIn,铬,黑,T(EBT),810,蓝,红,Mg,2+,Zn,2+,Pb,2+,二甲酚橙,(XO),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,指示剂的氧化变质现象,指示剂的僵化现象,PAN,溶解度小,需加乙醇、丙酮或加热,三,.,终点误差,E,t,=,100%,Y,ep,-M,ep,c,M,sp,pM=pM,ep,-pM,sp,M,ep,=,M,sp,10,-pM,Y,ep,=,Y,sp,10,-pY,Y,sp,10,-pY,-,M,sp,10,-pM,c,M,sp,E,t,=100%,pM,=-pY,M,sp,=Y,sp,=,c,M,sp,/,K,MY,E,t,=,10,pM,-10,-pM,c,M,sp,K,MY,例题：,pH=10,的氨性,buffer,中，以,EBT,为指示剂,用,0.02mol/L EDTA,滴定,0.20mol/L Ca,2+,计算,TE%,，若滴定的是,0.02mol/L Mg,2+,E,t,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+1)=6.10,EBT:,EBT(H),=1+H,+,/,K,a2,+H,+,2,/,K,a2,K,a1,=40,lg,EBT(H),=1.6,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,-10,2.3,10,-2,10,10.24,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,-0.3,10,-2,10,8.25,6.5,准确滴定与分别滴定判别式,一,.,准确滴定判别式,若,pM=0.2,要求,E,t,0.1%,根据终点误差公式,可知需,lg,c,M,sp,K,MY,6.0,若,c,M,sp,=0.010molL,-1,时,则要求,lg,K,8.0,多种金属离子共存 例：,M,，,N,存在时,分步滴定可能性的判断,lg,c,M,sp,K,MY,6.0,，考虑,Y,的副反应,Y(H),K,NY,M +Y =MY,K,MY,=,K,MY,/,Y,Y,=,Y(H),+,Y(N),-1,H,+,N,NY,H,n,Y,Y(H),Y(N),Y(H),Y(N),时，,Y,Y(H),（相当于,N,不存在）,Y(H),Y(N),时，,Y,Y(N),(,不随,pH,改变,),pH,低,Y(H),=,Y(N),时,的,pH,pH,高,仍以不生成沉淀为限,P,200,例题,20,M,、,N,共存时,lg,K,MY,与,pH,的关系,lg,a,Y(H),lg,a,Y,lg,a,Y(N),lg,a,pH,pH,lg,K,MY,lg,K,MY,M,，,N,共存，且,lgc,K,5,一,.,络合掩蔽法 加络合掩蔽剂,降低,N,Y(N),Y(H,),lg,K,MY,=lg,K,MY,-lg,Y(N),Y(N),1,+,K,NY,N,K,NY,c,N,/,N(L),Y(,H,),Y(,N),lg,K,MY,=lg,K,MY,-lg,Y(H),N,被完全掩蔽,M +Y =MY,H,+,N,NY,H,n,Y,L,H,n,L,NL,n,Y(H),Y(N),N(L),L(H),H,+,络合掩蔽注意事项：,2.,掩蔽剂与干扰离子络合稳定,:,N(L),=1+L,1,+L,2,2,+,大、,c,L,大且,1.,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,Co,2+,Ni,2+,Cu,2+,Zn,2+,F,-,掩蔽,Al,3+,;,3.,合适,pH,F,-,pH4;CN,-,pH10),P,204,例题,21,、,22,二,.,沉淀掩蔽法,例：,Ca,2+,Mg,2+,混合溶液中,Ca,2+,的测定,lg,K,CaY,=10.7,lg,K,MgY,=8.7,p,K,sp,:Ca(OH),2,=4.9,Mg(OH),2,=10.4,加沉淀剂,降低,N,Ca,2+,Mg,2+,Ca,2+,Mg(OH),2,CaY,Mg(OH),2,pH12,Y,Ca,指示剂,常用沉淀剂,掩蔽剂,被沉淀离子,被滴定离子,pH,指示剂,NH,4,F,Ca,2+,、,Mg,2+,、,Sr,2+,、,Ba,2+,、,RE,3+,Cu,2+,、,Cd,2+,、,Mn,2+,10,铬黑,T,NH,4,F,Ca,2+,、,Mg,2+,、,Sr,2+,、,Ba,2+,、,RE,3+,Cu,2+,、,Co,2+,、,Ni,2+,10,紫脲酸铵,K,2,CrO,4,Ba,2+,Sr,2+,10,MgY+,铬黑,T,Na,2,S,Cu,2+,、,Cd,2+,、,Hg,2+,、,Pb,2+,、,Bi,3+,Ca,2+,、,Mg,2+,10,铬黑,T,三,.,氧化还原,掩蔽法,FeY,lg,K,BiY,=27.9,lg,K,FeY,-,=25.1,lg,K,FeY,2-,=14.3,红,黄,抗坏血酸,(Vc),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+,四,.,其它,滴定剂的应用,Mg,2+,Ca,2+,Sr,2+,Ba,2+,lg,K,M-EDTA,8.7,10.69,8.73,7.86,lg,K,M-EGTA,5.21,10.97,8.50,8.41,EGTA:,乙二醇二乙醚二胺四乙酸,一,.,直接滴定法,:,6.8,络合滴定方式及其应用,例 水硬度的测定,:Ca,2+,、,Mg,2+,lg,K,CaY,=10.7 lg,K,MgY,=8.7,在,pH=10,的氨性缓冲溶液中，,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,lgc,K,6,络合反应速率快,有敏锐指示剂指示终点，不发生封闭,被测离子不水解，不沉淀,封闭指示剂 被测,M,与,Y,络合反应慢 易水解,例,Al,3+,的测定,二,.,返滴定法,Al,3+,AlY,Y,过量,AlY,ZnY,pH3.5,过量,Y,加热,pH5,6,冷却,Zn,2+,黄,红,XO,置换金属离子：被测,M,与,Y,的络合物不稳定,例,Ag,与,EDTA,的络合物不稳定,lg,K,AgY,=7.3 lg,K,NiY,=18.6,2Ag,+,+Ni(CN),4,2-,2Ag(CN),2,-,+Ni,2+,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,三,.,置换滴定法,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,pH3,4,Y,过,加热,Zn,2+,F,-,加热,Zn,2+,(,测,Al),(,测,Al,Pb,总量,),pH5,6,冷却,XO,黄,红,冷却,黄,红,测非金属离子,:PO,4,3-,、,SO,4,2-,待测,M,与,Y,的络合物不稳定,:K,+,、,Na,+,四,.,间接滴定法,五,.,络合滴定结果的计算,P,212,例题,23,、,24,、,25,总结：,络合平衡,副反应系数,Y(H),Y(N),M,条件稳定常数,K,MY,pM,sp,和,pM,ep,(pM,t,),及,Et,滴定酸度控制,共存离子分步滴定,滴定方式及应用,