Question

To avoid the precipitation of hydroxides of $N{i}^{2+}$, $C{o}^{2+}$, $Z{n}^{2+}$, and $M{n}^{2+}$ along with those of $F{e}^{3+}$, $A{l}^{3+}$, and $C{r}^{3+}$ the third group solution should be :

• A. Heated with a few drops of $conc.HN{O}_3$
• B. Treated with excess of $N{H}_{4}Cl$
• C. Concentrated
• D. None of these

Answer 1

The correct option is B Treated with excess of $N{H}_{4}Cl$

Option (B) is correct.
The third group solution should be treated with excess of $N{H}_{4}Cl$.
The presence of $N{H}_{4}Cl$ in excess reduces degree of dissociation of $N{H}_{4}OH$ to a considerable amount, and thus, $\left[O{H}^{-}\right]$ is just sufficient to cross over the ionic concentration product of hydroxides of III group elements to their $K_{sp}$.