# Why is a buffer solution used?

Why? Well to prevent GROSS changes in $p H$.
$p H = p {K}_{a} + {\log}_{10} \left\{\frac{\left[{A}^{-}\right]}{\left[H A\right]}\right\}$
This expression is derived in the link, along with some of the implications. When you do a titration of a weak acid, the POINT of half-equivalence, i.e. when $\left[H A\right] = \left[{A}^{-}\right]$, which may easily be interpolated from a graph, is the $p {K}_{a}$ of the acid? Why?