# Why is ammonia considered a base?

Apr 22, 2018

It's a Bronsted base because it can accept a proton.

#### Explanation:

The Brondsted-Lowry definition defines bases as substances that accept protons, or ${H}^{+}$ ions, in an aqueous solution.

When ammonia, $N {H}_{3}$, is placed into an aqueous solution, this reaction will occur:

$N {H}_{3} \left(a q\right) + {H}_{2} O \left(l\right) r i g h t \le f t h a r p \infty n s N {H}_{4}^{+} \left(a q\right) + O {H}^{-} \left(a q\right)$

We can see that $N {H}_{3}$ is accepting an ${H}^{+}$ ion from ${H}_{2} O$.

The forward reaction doesn't occur that readily, so, although ammonia is a base, it's a weak base.

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If we were to be really specific, ammonia sometimes also behaves as an acid by donating an ${H}^{+}$ ion.
This would make ammonia amphoteric, which means that it can behave as both an acid and a base.

$N {H}_{3} \left(a q\right) + {H}_{2} O \left(l\right) r i g h t \le f t h a r p \infty n s N {H}_{2}^{-} \left(a q\right) + {H}_{3} {O}^{+} \left(a q\right)$

BUT, the above reaction (when ammonia is behaving as an acid) happens at a way lower rate than when ammonia accepts a proton, so we call it a base.