Question

Ammonium ion is:

• A. neither an acid nor base
• B. both an acid and a base
• C. a conjugate acid
• D. a conjugate base

Answer 1

The correct option is C a conjugate acid

Ammonia is a base because it is accepting hydrogen ions from the water. The ammonium ion is its conjugate acid - it can release that hydrogen ion again to reform the ammonia.

$N{H}_3\left(aq\right)+H_{2}O\rightleftharpoons N{H}_4^{+}\left(aq\right)+O{H}^{-}\left(aq\right)$

There are two conjugate pairs:$N{H}_{3}and{N{H}_4}^{+},H_{2}OandO{H}^{-}$.

Looking at it from the other side, the ammonium ion is an acid, and ammonia is its conjugate base. The hydroxide ion is a base and water is its conjugate acid.