Question

Define: Acidic buffer solution. Write the relationship between solubility and solubility product for PbI\(_2\).

Hint:

Acidic buffers use weak acid-conjugate base pairs; for sparingly soluble salts, express \( K_{sp} \) in terms of solubility S.

Answer 1

Definition: An acidic buffer solution is a mixture of a weak acid and its conjugate base (or salt), maintaining a relatively constant pH (below 7) by resisting changes upon addition of small amounts of acid or base. Example: CH\(_3\)COOH and CH\(_3\)COONa.
Relationship for PbI\(_2\): For PbI\(_2 \rightleftharpoons \text{Pb}^{2+} + 2\text{I}^-\), let solubility = \( S \, \text{mol L}^{-1} \). Then, \( [\text{Pb}^{2+}] = S \), \( [\text{I}^-] = 2S \). Solubility product: \[ K_{sp} = [\text{Pb}^{2+}][\text{I}^-]^2 = S \cdot (2S)^2 = 4S^3. \] % Quick tip