If the concentration of Pb2+ is found to be 2.3 x 10-9 mol/L in a saturated solution of Pb3(PO4)2, what is the Ksp of Pb3(PO4)2 ?

Question

This is my work thus far it is as far as I could get:

Ksp = [Pb2+] [Pb3(PO4)2]
= [2.3 x 10-9 mol/L][Pb3(PO4)2]

Answer 1

Try this:

Ksp = [Pb2+]^3 [PO4]^2
= (2.3E-9)^3 (2/3 * 2.3E-9)^2
= 4/9 * (2.3E-9)^5

Hardly soluble stuff. Notice if the Pb ion concentration is x, then the PO4 ion has to be 2/3 x.....from the ratios in the formula.