A mixture of a weak acid and its salt with a strong base serves as an acidic buffer.
CH3COOH(aq) + H2O(l) = CH3COO-(aq) + H3O+(aq)
CH3COOH is a weak acid, while CH3COO- is a weak base
So, if NaOH is added to the system the following reaction occurs:
CH3COOH(aq) + NaOH(aq) –> CH3COO-(aq) + H2O(l) + Na+(aq)
The reaction shows that some acetic acids react with the OH- from the base and converts it to water. Therefore, the pH will not change as drastically as it would have without the buffer. Sodium acetate ionizes completely providing the acetate ion, CH3COO-.