1、北京大学定量分析化学简明教程习题第四章 络合滴定法1已知铜氨络合物各级不稳定常数为: K不稳17.810-3 K不稳21.410-3 K不稳33.310-4 K不稳47.410-5 (1) 计算各级稳定常数K1K4和各积累常数1-4; (2) 若铜氨络合物水溶液中Cu(NH3)42+的浓度为Cu(NH3)32+的10倍,问溶液中NH3是多少? (3) 若铜氨络合物溶液的CNH3=1.010-2M,CCu2+=1.010-4M,(忽略Cu2+,NH3的副反应)。计算Cu2+与各级铜氨络合物的浓度。此时溶液中以那种形体为最主要? 解:(1) 稳定常数 K1 K2= K3= K41.3102各级累积
2、常数 1K1=1.4104 2K1K21.43.01074.2107 3K1K2K31.43.07.1109=3.01010 4K1K2K3K4=1.43.07.11.310113.91012(2) 3=,4= = NH3=10=0.077(ml/l)(3) 0= 1.410-5 1 1.910-3 2 0.058 3 0.41 4 0.53答:主要形体为Cu(NH3)32+和Cu(NH3)42。2(1)计算pH5.5时EDTA溶液的lgY(H)值; (2)查出pH 1,2,10时EDTA的lgY(H)值,并在坐标纸上做出lgY(H)-pH曲线,由图查出pH5.5时的lgY(H)值,与计算值相
3、比较。 解:Y(H)1+1H+2H+2+3H+3+4H+4+5H+56H+6 1+104.84+105.58+102.78+100.65+104.55+109.15 104.84+105.58 6.9104+3.8105 4.2105 lgY(H)=5.63计算lgCd(NH3)、lgCd(OH)和lgCd值。(Cd2+-OH-络合物的lg1lg4分别是4.3、7.7、10.3、12.0)。 (1) 含镉溶液中NH3=NH4+=0.1; (2) 加入少量NaOH于(1)液中至pH为10.0。 解:(1) Cd(NH3)=1+1NH3+2NH32+3NH33+4NH34+5NH35+6NH36
4、=1+102.60-1.0+104.65-2.0+106.04-3.0+106.92-4.0+106.6-5.0+104.9-6.0=102.65+103.04+102.92=2.4103=103.38 lgCd(NH3)=3.38 当NH3=NH4+=0.1 pH=pKa=9.25,pOH=4.75 Cd(OH-)=1+1OH-2OH-23OH-34OH-41+104.3-4.75+107.7-9.5+1010.3-14.25+1012.0-19.01+10-0.45+10-1.81.4 lgCd(OH)0.14 Cd(OH)Cd(NH3)Cd(OH)1103.38+100.14-1103.
5、38 lgCd3.383.4(2) pH=10.0 H+=Ka =5.610-10 =0.17(mol/l) =10-0.77 Cd(NH3)=1+1NH3+2NH32+3NH33 +4NH34+5NH35+6NH36 =1+102.60-0.77+104.65-1.54+106.04-2.31+106.92-3.08 +106.6-3.85+104.9-4.62 =1+101.83+103.11+103.73+103.84+102.75+100.28 =104.15 lgCd(NH3)=4.15 Cd(OH)=1+1OH-+2OH-2+3OH-3+4OH-4 =1+104.3-4.0+107
6、.7-8.0+1010.3-12.0+1012.0-16.0 =1+100.3+10-0.3+10-1.7 =3.52 =100.55 lgCd(OH)=0.55 Cd=Cd(NH3)+Cd(OH)-1=104.15+100.55-1=104.15 lgCd=4.154计算下面两种情况下的lgNiY值 (1) pH9.0,CNH30.2M; (2) pH9.0,CNH3=0.2M,CCN-=0.01M。 解:(1) lgNiYlgKNiYlgNilgYNi(NH3)=1+1NH3+2NH32+3NH33+4NH34+5NH35+6NH36又:NH3=CNH3 0.07210-1.14 Ni(N
7、H3)=1+102.75-1.14+104.95-2.28+106.64-3.42+107.79-4.56+108.50-5.70+108.49-6.84 1+101.61+102.67+103.22+103.23+102.8+101.65 103.66 Y(H)101.4 lgNiY18.6-3.66-1.413.54(2) Ni(CN-)=1+4OH-4pH=9.0 =3.310-3=10-2.5Ni(CN-)=1+1031.3-101021.3NiNi(NH3)+Ni(CN-)+Ni(OH-)-2 103.66+1021.3+100.1-2 1021.3Y(H)101.4 lgNiYlg
8、NiYlgYlgNi18.6-1.4-21.3-4.15以210-2M EDTA滴定用浓度的Pb2+溶液,若滴定开始时溶液的pH=10,酒石酸的分析浓度为0.2M,计算等当点时的lgPbY,和酒石酸铅络合物的浓度。(酒石酸铅络合物的lgK为3.8)。 解:L=CL 0.2 0.2(mol/l)到等当点时 L=0.1 mol/lPb(L)=1+1L =1+103.8-1 =102.8Pb(OH-)=102.7Pb=Pb(L)+Pb(OH-)-1 =102.8+102.7-1 =103.05Y(H)=0.5lgPbY=lgPbY-lgY-lgPb =18.0-0.5-3.05 =14.4peg=(pCPbeg+lgPbY) =(2+14.4) =8.2注意eg还包括羟基络合物,正确的称法是Pb2+=PbL=KPbLPb2+L=103.8-11.3-1.0=10-8.5