# Is the purpose of a buffer system to keep a solution neutral? If not, what is the purpose?

Feb 15, 2017

The purpose of an (aqueous) buffer is to maintain the $p H$ of the given solution around a given value.........

#### Explanation:

The buffer equation, which is derived in the later link is:

${\log}_{10} {K}_{a} = {\log}_{10} \left[{H}_{3} {O}^{+}\right] + {\log}_{10} \left\{\frac{\left[{A}^{-}\right]}{\left[H A\right]}\right\}$

Upon rearrangement:

$- {\log}_{10} \left[{H}_{3} {O}^{+}\right] = - {\log}_{10} {K}_{a} + {\log}_{10} \left\{\frac{\left[{A}^{-}\right]}{\left[H A\right]}\right\}$

And upon simplification:

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

The $p H$ could be neutral, or ACIDIC, or BASIC, depending on $p {K}_{a}$, or the proportions of acid or base used.

A buffer then acts to keep the $p H$ tolerably close to the $p {K}_{a}$ of the starting acid. If the buffer is composed of equal concentrations of acid and conjugate base, $p H = p {K}_{a}$; why?

Depending on the capacity of the buffer, addition of small quantities of ${H}_{3} {O}^{+}$ or $H {O}^{-}$ protonate the conjugate base or deprotonate the acid, such that the $p H$ remains fairly close to a predetermined value. Biological systems (including our digestion and respiration processes) are extensively buffered.