Question

In the reaction \[{{H}_{2}}S\rightleftharpoons 2{{H}^{+}}+{{S}_{2}}^{-}\] when $N{{H}_{4}}OH$ is added, then
A. Sulphide ion is precipitate
B. No action takes place
C. Concentration of sulphide ion decreases
D. Concentration of sulphide ion increases

Answer 1

Hint: A basic species releases hydroxyl ion and an acidic species releases hydrogen ion. Thus when a basic species is added to an acidic species it will neutralise the hydrogen ion and increase the concentration of other ions formed from the acidic or basic species.

Complete Step by Step Answer:
Hydrogen sulphide is a weak acid. It dissociates in solution as hydrogen ion and sulphide ion. The dissociation is given as follows:
\[{{H}_{2}}S\rightleftharpoons 2{{H}^{+}}+{{S}_{2}}^{-}\]

Ammonium hydroxide is a weak base. It dissociates into ammonium ions and hydroxyl ions in solution.
The dissociation is as follows:
\[N{{H}_{4}}OH\rightleftharpoons N{{H}_{4}}^{+}+O{{H}^{-}}\]

Thus in the reaction of hydrogen sulphide when ammonium hydroxide is added the hydroxyl ion will react with the hydrogen ion of the hydrogen sulphide and form water. Thus a neutralisation reaction takes place. So, the concentration of the corresponding sulphide ion increases.

So, we can say that in the reaction of hydrogen sulphide when ammonium hydroxide is added the concentration of the corresponding sulphide ion increases.
Thus the correct option is D.

Note: Ammonium hydroxide is a weak base. It acts as an electrolyte in solution. It is prepared by mixing ammonia with water. Hydrogen sulphide is a hydride of sulphur, the group $16$ element.