Question

For the purpose of systematic qualitative analysis, cations are classified into various groups on the basis of their behaviour against some reagents. The group reagents used for the classification of most common cations are hydrochloric acid. hydrogen sulphide, ammonium hydroxide, and ammonium carbonate.
Classification is based on whether a cation reacts with these reagents by the formation of precipitates or not.

Which one among the following pairs of ions can be separated by $H_{2}S$ in presence of dilute hydrochloric acid?

• A. $B{i}^{3+},C{d}^{2+}$
• B. $A{l}^{3+},H{g}^{2+}$
• C. $Z{n}^{2+},C{u}^{2+}$
• D. $N{i}^{2+},C{u}^{2+}$

Answer 1

The correct option is A $B{i}^{3+},C{d}^{2+}$

Both $B{i}^{3+}$ and $C{d}^{2+}$ will be precipitated as $B{i}_2{S}_3$ (black) and $CdS$ (yellow) by $H_{2}S$in presence of dilute hydrochloric acid as both have low values of $K_{sp}$ than $A{l}^{3+},Z{n}^{2+}$ and $N{i}^{2+}$.