Question

When $H_{2}S$ gas is passed through $HCl$ containing aqueous solution of $CuC{l}_2$, $HgC{l}_2$, $BiC{l}_2$, and $CoC{l}_2$, it does not precipitate out:

• A. $CuS$
• B. $HgS$
• C. $B{i}_2{S}_3$
• D. $CoS$

Answer 1

The correct option is D $CoS$

Option (D) is correct.
When $H_{2}S$ gas is passed through $HCl$ containing aqueous solution of $CuC{l}_2$, $HgC{l}_2$, $BiC{l}_2$, and $CoC{l}_2$, it does not precipitate out $CoS$ as it belongs to IV group radical.
In the II group, the lower concentration of $S^{2-}$ ions can be achieved by passing $H_{2}S$ gas by passing through the solution of the salts in presence of $HCl$. $HCl$ suppressess the degree of ionisation of $H_{2}S$ by common ion effect.