In the systematic analysis of cations, Group II radicals are precipitated by passing gas in the pres — Qualitative and Quantitative Analysis Chemistry Question

💡 Solution & Explanation

$HCl$ provides a high concentration of $H^+$ ions, which suppresses the ionization of weak acid $H_2S$ (common ion effect). The resulting low $[S^{2-}]$ is only sufficient to precipitate the low- $K_{sp}$ Group II sulphides, leaving higher-group sulphides dissolved.