# Question #33da5

Aug 18, 2016

An aqueous solution for which $\left[H {O}^{-}\right] = 4.2 \times {10}^{-} 8 \cdot m o l \cdot {L}^{-} 1$ is slightly acidic.
For neutrality under standard conditions $\left[{H}_{3} {O}^{+}\right] = \left[H {O}^{-}\right] = {10}^{-} 7 \cdot m o l \cdot {L}^{-} 1$.
Alternatively since, $p H + p O H = 14$, where $p H = - {\log}_{10} \left[{H}_{3} {O}^{+}\right]$, if $p H < 7$, then the solution is acidic.
Here $p O H = 7.38$, thus $p H = 6.62$.