# How do buffers resist pH change?

$p H = p {K}_{a} + {\log}_{10} \left\{\frac{\left[{A}^{-}\right]}{\left[H A\right]}\right\}$
And thus an equimolar solution of a weak acid and its conjugate base will maintain a $p H$ close to the $p {K}_{a}$ of the acid should small quantities of acids or bases be added. Biological systems are extensively buffered.