# How do you predict the pH of a buffer solution using the Henderson-hasselbalch equation?

Jan 18, 2017

#### Answer:

It should be fairly close to the $p {K}_{a}$ of the weak acid used in the buffer.

#### Explanation:

See this old answer. For the weak acid $H A$ mixed with appreciable quantities of its conjugate base:

$p H = p {K}_{a} + {\log}_{10} \left\{\frac{\left[{A}^{-}\right]}{\left[H A\right]}\right\}$

Clearly, when $\left[{A}^{-}\right] = \left[H A\right]$, then $p H = p {K}_{a}$. Why so? The $p H$ at the point of half-equivalence is therefore used to measure $p {K}_{a}$.