Question

Precipitation of IV group cations takes place when $H_{2}S$ passed is :

• A. less ionized
• B. highly ionized
• C. not ionized
• D. none of these

Answer 1

The correct option is B highly ionized

Precipitation of IV group cations takes place when $H_{2}S$ passed is highly ionised.
Radicals of Group IV are also precipitated as their sulphides. But the solubility products of their sulphides are quite high. In order that ionic products exceed solubility products, concentration of $S^{2-}$ ions should be high in this case. High concentration of $S^{2-}$ ions is achieved by passing $H_{2}S$ gas through the solution of the salts in the presence of $N{H}_{4}OH$. Hydroxyl ions from $N{H}_{4}OH$ combine with $H^{+}$ ions from $H_{2}S$. Due to the removal of $H^{+}$ ions the equilibrium of $H_{2}S$ shifts in favour of ionised form.
Hence concentration of $S^{2-}$ ions increases. With this increased concentration of $S^{2-}$ ions, ionic products exceed solubility products and the radicals of Group IV get precipitated as sulphides.