Cd2+ and Pb2+ ions in a polluted water sample are measured bycomplexation. In a first titration, 50.00 mL of water at pH 10 istitrated by 40.09 mL of 0.004870 M EDTA. In a second titration, a75.00 mL aliquot of water is first treated with an excess of KCN tomask the cadmium in Cd(CN)4 2- before being titrated by 31.44 mL ofthe same EDTA solution. Calculate the concentrations of Cd2+ andPb2+ in the polluted water sample. Cd2+ + 4 CN- <===> Cd(CN)4Kf = 1.0 x 10^19 Cd2+ + Y4- <===> CdY2- Kf = 2.9 x 10^16 Pb2++ Y4- <===> PbY2- Kf = 1.1 x 10^18 aY4- = 0.36
