• # question_answer Discuss the role of $N{{H}_{4}}OH$  in group III of basic radicals.

In group III, the cations $F{{e}^{3+}},\,C{{r}^{3+}}$ and $A{{l}^{3+}}$  are precipitated as hydroxides by the addition of $N{{H}_{4}}OH$ to the aqueous solution of the mixture. But a small amount of $N{{H}_{4}}Cl$  (common $NH_{4}^{+}$ ion) is added before the addition of $N{{H}_{4}}OH$. Its purpose is to suppress the $NH_{4}^{+}$ ion concentration in solution due to common ion effect. Thus, only the hydroxides of cations of group III (low ${{K}_{sp}}$ values) will be precipitated while the hydroxides of cations of higher groups will remain in solution since their ${{K}_{sp}}$ values are higher and the products will remain less than their solubility product $({{K}_{sp}})$ values.