# If pH=5.25, what is [H_3O^+]?

Apr 27, 2016

$\left[{H}_{3} {O}^{+}\right]$ $=$ ${10}^{- 5.25} \cdot m o l \cdot {L}^{-} 1$.
$p H$ $=$ $- {\log}_{10} \left[{H}_{3} {O}^{+}\right]$.
When we write, ${\log}_{a} b$, we ask to what power we raise the base $a$ to get $b$. Thus ${\log}_{10} 100 = 2$, and ${\log}_{10} 0.1 = - 1$.