Question

How do you make a buffer in chemistry?

Answer 1

Take a weak acid, and add `"HALF AN EQUIV"` of a strong base.

Explanation:

Take a weak acid, and add `"HALF AN EQUIV"` of a strong base. And `pH` is governed by the relationship:

`pH=pK_a+log_10{[[A^-]]/[[HA]]}`

In the scenario I proposed, `pH=pK_a` because `[HA]=[A^-]` (and `log_(10)1=0`). If I wanted a solution buffered to a particular `pH` I would choose a weak acid with a `pK_a` CLOSE to the `pH` I wanted to maintain. Of course, I could vary the `pH` of the buffer up or down by jiggering the concentrations of `H_3O^+` and `HO^-` appropriately.

See here for a fuller treatment.