What does a pH scale measure?

Sep 25, 2016

It measures $\left[{H}_{3} {O}^{+}\right]$, i.e. hydronium ion concentration.

Explanation:

And $p H = - {\log}_{10} \left[{H}_{3} {O}^{+}\right]$

$\left[{H}_{3} {O}^{+}\right]$ derives from water's autoprotolysis:

$2 {H}_{2} O \left(l\right) r i g h t \le f t h a r p \infty n s {H}_{3} {O}^{+} + H {O}^{-}$

At $298 K$, ${K}_{a} = {10}^{-} 14$, and thus $p H + p O H = 14$