Question

Silver chromate is sparingly soluble in aqueous solutions. The Ksp of Ag2CrO4 is 1.12× 10–12. What is the solubility (in mol/L) of silver chromate in 1.00 M potassium chromate aqueous solution?

Answer 1

This is an example of the common ion effect. The common ion in this case is CrO4^2- from K2CrO4.
............Ag2CrO4 ==> 2Ag^+ + CrO4^2-
solubility.....x........2x.........x

.......K2CrO4 ==> 2K^+ + CrO4^2-
initial..1M.........0......0
change...-1M........1M.....1M
equil.....0.........1M.......1M

Ksp Ag2CrO4 = (Ag^+)^2(CrO4^2-)
(Ag^+) = 2x from Ag2CrO4--see chart above.
(CrO4^2-) = x from Ag2CrO4 + 1M from K2CrO4
Substitute into Ksp expression and solve for x.
Post your work if you get stuck.

Answer 2

I got to 4x^3 + 6x^2=1.12x10^-12 (my moles of potassium chromate is 1.5 instead of 1) but now I'm stuck