Question

In a saturated solution of silver phosphate, the concentration of silver is 4.5 x 10^-4 mol/L. What is the Ksp of silver phosphate?

Answer 1

Ag3PO4(s) <=> 3Ag^+(aq) + PO4^3+(aq)
Ksp = [Ag^+]^3•[PO4^3+]
Let [PO4^3+] = s
then [Ag^+]= 3s = 4.5 x 10^-4 mol/L.
s = 1.5x10^-4
Ksp = (3s)^3•(s) = 27s^4
substitute the value of s and solve

Answer 2

GK made a a couple of typos. PO4^3+ should have been PO4^3-. That doesn't change anything in the calculation.