$\mathrm{In} \mathrm{qualitative} \mathrm{analysis}, \mathrm{in} \mathrm{order} \mathrm{to} \mathrm{detect} \mathrm{second} \mathrm{group} \mathrm{basic} \mathrm{radical}, \mathrm{a} \mathrm{mixture} \mathrm{of} {\text{HCl+H}}_{\text{2}}\text{S} \mathrm{is} \mathrm{used} \mathrm{to}$

$$\begin{gathered} \mathrm{HCl} \mathrm{suppresses} \mathrm{ionization} \mathrm{of} \mathrm{weakly} \mathrm{dissociated} H_{2}S , \mathrm{with} \mathrm{the} \mathrm{result}, \mathrm{only} \mathrm{the} \mathrm{ionic} \mathrm{product} \mathrm{of} \mathrm{the} \mathrm{sulfides} \\ \mathrm{of} \mathrm{group} \mathrm{II} \mathrm{radicals} \mathrm{exceed} \mathrm{their} \mathrm{corresponding} \mathrm{solubility} \mathrm{product}, \mathrm{hence}, \mathrm{only} \mathrm{these} \mathrm{are} \mathrm{precipitated}. \end{gathered}$$