# How do you calculate the pH of a buffer?

$p H = p {K}_{a} + {\log}_{10} \left\{\frac{\left[{A}^{-}\right]}{\left[H A\right]}\right\}$
And thus in equimolar quantities of weak acid and conjugate base, the $p H$ of the buffer is equal to the $p {K}_{a}$ of the weak acid. Why?