Question

Solid Nal is slowly added to a solution that is .0040 M in Cu^+. Calculate the [I-] when CuI just begins to precipitate from the solution.

Answer 1

CuI ==> Cu^+ + 2^-

Ksp = (Cu^+)(I^-)
You know Ksp, you know I^-, you're left with only one unknown; i.e., (Cu^+). Solve for that.