A solution contains 2.0*10^-3 M Pb^2+ and 1.0*10^-4 M Cu^+. I^- is added to the solution little by little, will CuI (Ksp=1.0*10^-12) or PbI2 (Ksp=7.9*10^-9) precipitate first? Determine the concentration of I^- required to commence precipitation of each salt.