# What is the pH of a solution if the [H^+] = 3.45 * 10^-9 M?

$p H$ $=$ $- {\log}_{10} \left[{H}^{+}\right]$
$p H$ $=$ $- {\log}_{10} \left\{3.45 \times {10}^{-} 9\right\}$ $=$ $8.5$.
This value is reasonable in that since $\left[{H}^{+}\right] < {10}^{- 7}$, the solution is slightly basic, and the $p H$ of course reflects this.