# What is the "pH" for 2.5 xx 10^(-6) "M" "HCl"?

Jun 2, 2016

$p H = 5.60$

#### Explanation:

HCl is a strong acid that fully ionizes when dissolved in water according to the following equation:

$H C l + {H}_{2} O \to {H}_{3} {O}^{+} + C {l}^{-}$

Having 1:1 ratio $\implies \left[{H}_{3} {O}^{+}\right] = 2.5 \times {10}^{-} 6 \setminus M$

$p H = - \log \left[{H}_{3} {O}^{+}\right]$
$p H = - \log \left(2.5 \times {10}^{-} 6\right)$
$p H = 5.60$

Note that the contribution of the autoionization of ${H}_{2} O$ to $\left[{H}_{3} {O}^{+}\right]$ is small (in the range of ${10}^{-} 7 M$) that is why it is neglected. If it was not, it may contribute about one-tenth or so to the $\text{pH}$.