Question

what is [Ag^+] in a solution formed by mixing 25.0 ml of 0.10 M AgNO3 with 50.0 ml of 1.50 M Na3PO4. Ksp for Ag3PO4=1.0x10^-21

Answer 1

millimols AgNO3 = mL x M = 25*0.1 = 2.5
millimols Na3PO4 = 50 x 1.5 = 75
......3AgNO3 + Na3PO4 ==> Ag3PO4 + 3NaNO3
I......2.5......75..........0........0
C.....-2.5.....-2.5/3......2.5/3....2.5
E.......0.......74.17.......0.8333..2.5

For solubility product with the PO4^3- as the common ion, you have
.............Ag3PO4 --> 3Ag^+ + PO4^3-
I............solid.......0.......0
C............solid.......3x......x
E............solid.......3x......x

Then Ksp = (Ag^+)^3(PO4^3-)
(Ag^+) = solive for this
(PO4^3-) = M = mmols/mL = 74.17/75 = ?