# How do you make a buffer in chemistry?

Dec 27, 2016

Take a weak acid, and add $\text{HALF AN EQUIV}$ of a strong base.

#### Explanation:

Take a weak acid, and add $\text{HALF AN EQUIV}$ of a strong base. And $p H$ is governed by the relationship:

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

In the scenario I proposed, $p H = p {K}_{a}$ because $\left[H A\right] = \left[{A}^{-}\right]$ (and ${\log}_{10} 1 = 0$). If I wanted a solution buffered to a particular $p H$ I would choose a weak acid with a $p {K}_{a}$ CLOSE to the $p H$ I wanted to maintain. Of course, I could vary the $p H$ of the buffer up or down by jiggering the concentrations of ${H}_{3} {O}^{+}$ and $H {O}^{-}$ appropriately.

See here for a fuller treatment.