Silver cyanide, AgCN(s), has a molar solubility of 1.2 × 10−5 mol L−1 in pure water at 25 °C. A student investigates how changing the pH of the solution influences the equilibrium amount of dissolved silver ions.
(a) Predict qualitatively whether the molar solubility of AgCN(s) will be higher, lower, or unchanged when the pH is lowered to 2.0 by the addition of a strong acid. Justify your prediction without performing numerical calculations.
(b) Predict qualitatively whether the molar solubility of AgCN(s) will be higher, lower, or unchanged when the pH is raised to 12.0 by the addition of a strong base. Justify your prediction.
(c) Suppose that solid NaCN is added instead of acid or base, keeping the pH near neutrality while increasing the concentration of the CN− ion. Explain how this change would affect the solubility of AgCN(s) and compare the direction of the change with your answers in parts (a) and (b).