# If pH=12.5, what is [H^+]?

By definition, $p H$ $=$ $- {\log}_{10} \left[{H}_{3} {O}^{+}\right]$, equivalently, $- {\log}_{10} \left[{H}^{+}\right]$.
Thus, $\left[{H}^{+}\right]$ $=$ ${10}^{- 12.5}$ $m o l \cdot {L}^{-} 1$ =??