In the precipitation of soap (like sodium stearate, ) from its saturated aqueous solution, which com — Ionic Equilibrium Chemistry Question

💡 Solution & Explanation

Soap dissolves according to the equilibrium $C_{17}H_{35}COONa_{(s)} \rightleftharpoons C_{17}H_{35}COO^-_{(aq)} + Na^+_{(aq)}$. Adding a strong electrolyte like $NaCl$ drastically increases the $[Na^+]$ concentration. Because of the common ion effect, the ionic product exceeds the $K_{sp}$ of the soap, shifting the equilibrium backward and causing the soap to precipitate out (salting out).