Question

Conjugate acid of $N{{H}_{2}}^{-}$ is:
[A] $N{{H}_{4}}^{+}$
[B] $N{{H}_{3}}$
[C] $N{{H}_{2}}OH$
[D] $N{{H}^{-}}$

Answer 1

Hint: To answer this question, we will use the Bronsted-Lowry acid – base concept. According to this theory, it can be written as-
Acid+ Base $\rightleftharpoons $ Conjugate base + Conjugate acid.

Complete step by step answer:
As we know, according to the Bronsted-Lowry acid - base theory, a conjugate acid is a compound formed on receiving a proton $({{H}^{+}})$ by a base.
It can also be written that a conjugate acid is a base, with a hydrogen atom added to it as in the reverse reaction it will lose a hydrogen ion.

To find the conjugate acid of any compound, we will just need to add a proton, a ${{H}^{+}}$ to it and the resultant will be the conjugate of that compound.

Therefore, the conjugate acid of $N{{H}_{2}}^{-}$ will be-
\[N{{H}_{2}}^{-}+{{H}^{+}}\to N{{H}_{3}}\]

The positive charge of the hydrogen will neutralize the negative charge on the amide anion, hence the resultant conjugate acid will be neutral.
Therefore, the correct answer is option [B] $N{{H}_{3}}$

Additional Information:
The conjugate base of $N{{H}_{4}}^{+}$, ammonium ion is also $N{{H}_{3}}$, ammonia.
The most important application of this conjugate acid – base theory is a buffer solution. In a buffer, a weak acid and its conjugate base or a weak base and its conjugate acid is used in order to maintain the pH change of the reaction during titration.

Note: It is important here to remember that conjugate base is the compound which is left after an acid has donated its proton and a conjugate acid is the compound which is formed after a base receives a proton.