# How does pH relate to pKa?

Mar 23, 2018

$\text{pH}$ is the negative logarithm of the concentration of protons in solution as a result of dissolving the acid.

$p {K}_{\text{a}}$ is the negative logarithm of the equilibrium expression of the acid dissociating.

$H A r i g h t \le f t h a r p \infty n s {H}^{+} + {A}^{-}$, where

${K}_{a} = \frac{\left[{H}^{+}\right] \left[{A}^{-}\right]}{\left[H A\right]}$

To be sure, if the subject of each "power" is high, then it is consequently low in magnitude.

Thus, if something is very acidic, the concentration of protons is very high, and the numerator of the equilibrium expression will also be larger than the denominator.

Hence, both will be low for a strong acid, and both will be high for a strong base.