Question

A solution contains a group IV cation. It's sulphide precipitate dissolves in $dil.HCl$ on boiling. On addition of $NaOH$ to the dissolved sulphide precipitate solution in excess, a white precipitate is formed which turns brown due to atmospheric oxidation.
The cation is:

• A. $Z{n}^{2+}$
• B. $M{n}^{2+}$
• C. $N{i}^{2+}$
• D. $C{o}^{2+}$

Answer 1

The correct option is B $M{n}^{2+}$

Analysis of Group IV Cations:
Tests for Manganese ions $\left(M{n}^{2+}\right)$
Manganese sulphide precipitate dissolves in $dil.HCl$ on boiling
On addition of $NaOH$ solution in excess, a white precipitate of manganese hydroxide is formed which turns brown due to atmospheric oxidation into hydrated manganese dioxide
$MnS+2HCl\to MnC{l}_2+H_{2}S$

$MnC{l}_2+2NaOH\to \underset{\text{White ppt.}}{Mn(OH{)}_2}+2NaCl$

$Mn(OH{)}_2+[O]\to \underset{\text{Hydrated manganese dioxide}\text{(Brown colour)}}{MnO(OH{)}_2}$