Buffer Solution
A solution that resists changes in pH when small amounts of acid or base are added.
Unit
Dimensionless
In depth
A buffer contains appreciable amounts of both a weak acid and its conjugate base, so added H⁺ is absorbed by the base and added OH⁻ by the acid. The pH stays close to the pKa of the weak acid and shifts only slightly as the ratio of the two components changes.
Examples in the real world
Blood buffered near pH 7.4 by carbonic acid and hydrogencarbonate; ethanoic acid with sodium ethanoate.