(A) Show that Ag₂S(s) (K_spa = 6 x 10^-30) should precipitate and that FeS(s) K_spa = 6 x 10²) should not precipitate from a solution that is 0.010 M Ag⁺ and 0.020 M Fe²⁺, but otherwise under the same conditions as in Example 18-14.

Example 18-14

Show that PbS(s) will precipitate but FeS(s) will not precipitate from a solution that is 0.010 M in Pb²⁺, 0.010 M in Fe²⁺, saturated in H₂S (0.10 M H₂S), and maintained with [H₃O⁺] = 0.30 M. For PbS, K_spa = 3 x 10^-7; for FeS, K_spa = 6 x 10².

(B) What is the minimum pH of a solution that is 0.015 M Fe²⁺ and saturated in H₂S (0.10 M) from which FeS(s) (K_spa = 6 x 10²) can be precipitated?