# Given a solution of nitric acid whose pH=4, what are [H_3O^+], and [NO_3^(-)]?

Dec 30, 2016

$\left[H N {O}_{3}\right] = 0.0001 \cdot m o l \cdot {L}^{-} 1$

#### Explanation:

$p H = - {\log}_{10} \left[{H}_{3} {O}^{+}\right]$

We are given that $p H = 4$

And thus $\left[{H}_{3} {O}^{+}\right] = 0.0001 \cdot m o l \cdot {L}^{-} 1$ (since ${\log}_{10} 0.0001 = {\log}_{10} {10}^{-} 4 = - \left(- 4\right) = 4$.

In water, nitric acid would undergo complete dissociation, according to the following rxn:

$H N {O}_{3} \left(a q\right) + {H}_{2} O \left(l\right) \rightarrow {H}_{3} {O}^{+} + N {O}_{3}^{-}$

And thus the formal concentration of nitric acid is equivalent to $\left[{H}_{3} {O}^{+}\right]$ and $\left[N {O}_{3}^{-}\right]$.