Solid NaI is slowly added to a soln that is 0.0097 M ub Cu+ and 0.0089 M in Ag+...?

Question

Calculate [Ag+] when CuI begins to precipitate

What percent of Ag+ remains in solution at this point?

Answer 1

Ksp for AgI = 8.52x10^-17 and CuI = 1.27x10^-12 (see reference below).

Since Ksp(CuI) = [Cu+] [I-], then

1.27x10^-12 = (0.0097 M)  [I-]; solving,

[I-] = 1.31x10^-10 M when CuI starts to precipitate.

Since Ksp(AgI) = [Ag+] [I-], then

8.52x10^-17 = [Ag+] (1.31x10^-10 M); solving,

[Ag+] = 6.51x10^-7 M when CuI starts to precipitate.

The percent [Ag+] left at this point is

(100%) (6.51x10^-7 M) / (0.0089 M) = 0.0073%.