Question

The solubility products of AgCl and 𝐴𝑔3𝑃𝑂4 are 1.6 × 10−10 and 1.8 × 10−18, respectively. If 𝐴𝑔+ is added (without changing the volume) to 1.00 L of a solution containing 0.10 mol 𝐶𝑙− and 0.10 mol 𝑃𝑂4 3−, calculate the concentration of 𝐴𝑔+ions (in mol/L) required to initiate
(a) the precipitation of AgCl and
(b) the precipitation of 𝐴𝑔3𝑃𝑂4

Answer 1

What (Ag^+) is required to ppt AgCl and Ag3PO4 in separate solutions?
For AgCl it is (Ag^+) = (1.6E-10/0.1) = 1.6E-9 M
For Ag3PO4 it is (Ag^+) = (1.8E-18/0.1)^1/3 = 2.6E-6 M
(a) Therefore, Ag^+ added drop wise to the initial solution will ppt AgCl first when (Ag^+) = 1.6E-9 M and leave Ag3PO4 undisturbed.

(b) When (Ag^+) = 2.62E-6 M the Ag3PO4 will begin ppting.

Answer 2

Well done