Question

The cation that will not be precipitated by $H_{2}S$ in the presence of dil. $HCl$ is :

• A. $C{u}^{2+}$
• B. $A{s}^{3+}$
• C. $C{o}^{2+}$
• D. $P{b}^{2+}$

Answer 1

The correct option is C $C{o}^{2+}$

$C{o}^{2+}$ ion will not be precipitated by $H_{2}S$ in the presence of dil $HCl$ as dil. $HCl$ will suppress the ionization of $H_{2}S$
To affect the precipitation $H_{2}S$ should be used in the ammoniacal solution.
$C{o}^{2+}$~ion is precipitated by $H_{2}S$ in presence of $N{H}_{4}OH$ which is a group reagent of group $IV$ in cationic analysis.