分析化学-络合反应的副反应系数-金属离子的副反应系数M

2个副反应同时存在时[M] +[MOH] +M(OH),] + ---[MA] +[MA2] + ---dm[M][M] +[MOH] +M(OH),] + ... +[M]+[MA] +[MA,]+...-[M][M]= αM(OH) + αM(A) -若有n个副反应α m= α M(A1)+ α M(A2) +-----α M(An)-(n-1)

2个副反应同时存在时 2 M 2 [M]+[MOH]+M(OH) ]+-[MA]+[MA ]+- = ] - [M  2 2 [M]+[MOH]+M(OH) ]+ +[M + [MA]+[MA ]+ = [M]  ] -[M]  =  M(OH) M(A) + 1-  M =  M(A1)+  M(A2) +- M(An)-(n-1) 若有n个副反应

例2用EDTA滴定Zn2+至化学计量点附近pH = 11.00, [NH]=0.10mol·L-1,计算Ig αznαZn(NH3)一1+[NH3]β,+[NH3]2 β2+[NH3]3 β3+[NH3]4 β =1+10-1.00+2.27+10-2.00+4.61+10-3.00+7.01+10-4.00+9.06=1+101.27+102.61+104.01+105.06=105.10查附录IⅢI.6 , pH=11.00时, lgα zn(0H)=5.4Ig α zn= Ig(α Zn(NH3)+ α zn(OH)-1)=lg(105-1+1054-1)-10 5.6

例2 用EDTA滴定Zn2+至化学计量点附近, pH = 11.00，[NH3 ]=0.10mol·L-1 , 计算 lg Zn Zn(NH3)= 1+[NH3 ]1+[NH3 ] 2  2+[NH3 ] 3  3+[NH3 ] 4  4 =1+10-1.00+2.27+10-2.00+4.61+10-3.00+7.01+10-4.00+9.06 =1+101.27+102.61+104.01+105.06=105.10 查附录III.6 , pH=11.00时, lg Zn(OH)=5.4 lg  Zn= lg( Zn(NH3)+  Zn(OH)-1)=lg(105.1+105.4 -1)=10 5.6

例3用EDTA滴定Zn2+至化学计量点附近，pH = 9.0, c(NH)=0.10mol·L-1计算Ig α zn(NH3)Z[Zn(NH3);]c(NH)=[NH]+[NH +]+[NH,']忽略Ka(NH) = 10-9.37*(1 = 0.1)[NH.H(NH)= 1+[H*]KHαNH3(H)[NH3]= 100.5= 1+ 10-9.0+9.4

例3 用EDTA滴定Zn2+至化学计量点附近, pH = 9.0，c(NH3 )=0.10mol·L-1 , 计算lg  Zn(NH3) c(NH3 )=[NH3 ]+[NH4 +]+ ( ) ( ) ( ) ] 3 + H + NH 4 + -9.37* a 4 3 -9.0+9.4 0. 3 H 5 [NH = = 1+[H ] NH [NH ] = 1+1 (NH ) 1 = 0. = 0 = 0 1 K 0 I 1 K    3 [Zn(NH ) ]i  3 [NH ] 忽略

[NH,] - C(NH.0.1= 0.03 = 10-1.5 mol. L-1100.5αNH3(H)或：10-9.4x0.1[NH3] = Xo·c(NH3)== 0.03 mol.L+10-9.410-9.0αZn(NH3)1+[NH3]β,+[NH3]? β,+[NH,]3 β 3+[NH3]+ β = 103.2= 3.2Igαzn(NH3)

( ) ( ) 3 -1.5 -1 3 0.5 NH H 3 NH 0.1 NH = = = = 10 mol 0.03 1 : 0 L c      或  ( ) 3. = 3.2 H3 2 Zn N =10 lg Zn(NH3)= 1+[NH3 ]1+[NH3 ] 2  2+[NH3 ] 3  3+[NH3 ] 4  4 ( ) -1 -9.4 3 0 3 -9.0 -9.4 10 0.1 NH = NH = = 0.03 mol L 10 +10 x c       

3.络合物的副反应系数αMYMYM+Y=强酸碱性溶H+OH-液中要考虑MHYM(OH)Y计算：pH=3.0、5.0时的lgαznY(H)K(ZnHY)=103.0查附录表III.4 αznY(m)=1+10-3.0+3.0=2 , IgaznY(H)= 0.3pH=3.0,pH=5.0, aznY(H)=1+10-5.0+3.0-1, lgaznY(H)= 0

3. 络合物的副反应系数αMY M + Y = MY H+ OH￾MHY M(OH)Y 计算：pH=3.0、5.0时的lgαZnY(H) 强酸碱性溶 液中要考虑 查附录表III.4 K(ZnHY)=103.0 pH=3.0, αZnY(H)=1+10-3.0+3.0=2 , lgαZnY(H)= 0.3 pH=5.0, αZnY(H)=1+10-5.0+3.0=1, lgαZnY(H)= 0