Question

The concentration of which ion is to be decreased, when $N{{H}_{3}}$ solution is added
A. $O{{H}^{-}}$
B. $N{{H}^{+}}_{4}$
C. ${{H}_{3}}{{O}^{+}}$
D. ${{O}^{-}}_{2}$

Answer 1

Hint: The concentration of ${{H}_{3}}{{O}^{+}}$ ion is to be decreased, when we add $N{{H}_{3}}$ solution because $N{{H}_{3}}$ act as lewis acid and they give electron pair to ${{H}_{3}}{{O}^{+}}$ which act as a lewis base, which accepts the electron pair from $N{{H}_{3}}$.

Complete Step by Step Answer:
Ammonia is obtained when hydrogen and nitrogen react. It is lighter than air and it is highly soluble in water. It behaves like a weak base as it combines with acids to form salts. It also shows weak acidic behaviour therefore, it is amphoteric in nature.

It is highly soluble in water as there is a lone pair of electrons at the nitrogen. It is attracted to hydrogen in water molecule hydrogen bonding. The presence of hydrogen bonding between two molecules tells us that the molecules are polar.

When ammonia is added in water, then ammonium and the hydroxyl ion is released.
$N{{H}_{3}}+{{H}_{2}}O\to N{{H}^{+}}_{4}+O{{H}^{-}}$
It is an acid- base reaction. Thus, we see that the concentration of $N{{H}^{+}}_{4}$ and $O{{H}^{-}}$will increase and the concentration of ${{H}_{3}}{{O}^{+}}$ will decrease.
Thus, Option (C) is correct.

Note: According to Bronsted lowry concept, ammonia accepts a proton to form $N{{H}^{+}}_{4}$ ion so it acts as a base and the ammonium ion is the conjugate acid. The water molecules donate a proton to ammonia to generate $O{{H}^{-}}$ ion. Hence water acts as an acid and the $O{{H}^{-}}$ is the corresponding conjugate base.