Buffer Range
The span of pH values over which a buffer works effectively, conventionally one unit either side of its pKa.
Formula / equation
pH = pKa ± 1
Unit
Dimensionless
In depth
Outside this range the ratio of the two components exceeds ten to one, so one of them is too depleted to absorb further addition. Choosing a buffer therefore begins with selecting a weak acid whose pKa lies close to the target pH.
Examples in the real world
An acetate buffer covers pH 3.8 to 5.8; a phosphate buffer covering 6.2 to 8.2 is used for biological work.