# Why do buffers resist pH change?

May 28, 2016

Because they introduce a means for the solvent to sop up excess ${H}_{3} {O}^{+}$ and $H {O}^{-}$, and resist gross change in $p H$.

#### Explanation:

This equation is well-known:

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

Thus given quantities of acid and conjugate base, added ${H}_{3} {O}^{+}$ or $H {O}^{-}$ reacts with the base or the acid, and $p H$ change is moderated by the ${\log}_{10}$ term.

When a weak acid is titrated by a strong base, or a strong acid by a weak base, a buffer is formed initially, and this region of the graph of $p H$ versus volume of titrant is known as the buffer region.

Biological systems are extensively buffered, to reduce gross changes in $p H$.

For a fuller treatment, see this old answer.