# What is the "conjugate acid of ammonia", NH_3?

Mar 27, 2017

$\text{Ammonium ion}$, $N {H}_{4}^{+}$.

#### Explanation:

$\text{Conjugate acid/conjugate base pairs}$ are simply defined by proton exchange, i.e. addition or subtraction of ${H}^{+}$. As with any chemical reaction, charge and mass are conserved:

${\underbrace{N {H}_{4}^{+}}}_{\text{conjugate acid") rarrunderbrace(NH_3)_("conjugate base}} + {H}^{+}$

Ammonia is a good example for the $\text{conjugate acid/conjugate base relationship}$ because it shows how acid/base chemistry can be extended beyond aqueous solution, and in liquid ammonia the following equilibrium operates:

$2 N {H}_{3} \left(l\right) r i g h t \le f t h a r p \infty n s {\underbrace{N {H}_{4}^{+}}}_{\text{conjugate acid of ammonia") + underbrace(NH_2^(-))_("conjugate base of ammonia}}$

${K}_{\text{eq}}$ for this ammonolysis reaction is much smaller than for ${K}_{\text{eq}}$ in the water solvent.

$N {H}_{2}^{-}$ is the so-called $\text{amide ion}$; and is itself the conjugate acid of $N {H}^{2 -}$, $\text{imide ion}$, which is itself the conjugate acid of ${N}^{3 -}$, $\text{azide ion}$. These nitrogen bases are not encountered outside of liquid ammonia, a water-like solvent.

The take home message is that $\text{conjugate acid/conjugate base}$ pairs are defined by proton exchange, i.e. ${H}^{+}$. All (?) you have to do is balance mass and charge.

In liquid $H F$, (an actual solvent), what is the conjugate acid and what is the conjugate base? Use the same procedure as before.