Which of the following phenomena or processes strictly rely on the principle of the common ion effec — Ionic Equilibrium Chemistry Question

💡 Solution & Explanation

Salting out soap relies on added $Na^+$ to exceed $K_{sp}$. Purifying $NaCl$ relies on added $Cl^-$ from $HCl$ gas to precipitate pure $NaCl$. Suppressing $H_2S$ ionization relies on added $H^+$ from $HCl$ to lower $[S^{2-}]$ for Group II cation precipitation. The auto-ionization of pure heavy water is a spontaneous thermodynamic property and does not involve an externally added common ion.