2022 H2 Chem P1 Q15 — Solubility Solution

The answer is C (ammonia increases the solubility; sodium chloride decreases it).

\(\text{AgCl(s)} \rightleftharpoons \text{Ag}^+\text{(aq)} + \text{Cl}^-\text{(aq)}\)

• Aqueous ammonia: \(\text{NH}_3\) forms the soluble complex \([\text{Ag(NH}_3\text{)}_2]^+\) with \(\text{Ag}^+\), lowering \([\text{Ag}^+]\). The position of equilibrium shifts right, so more AgCl dissolves: solubility increases.
• Aqueous sodium chloride: the common ion \(\text{Cl}^-\) raises \([\text{Cl}^-]\), so the position of equilibrium shifts left and AgCl is precipitated: solubility decreases (common ion effect).

• A is wrong: ammonia increases the solubility, it does not decrease it.
• B is wrong: both entries are reversed; ammonia increases and sodium chloride decreases the solubility.
• D is wrong: sodium chloride decreases the solubility through the common ion effect.