The sodium acetate/acetic acid solution is an example of a buffer. It contains appreciable quantities of both a weak acid (acetic acid) and its conjugate base (acetate ion.) The buffer resists changes in pH by removing the ions that dissociate from an added strong acid or the ions that dissociate from an added strong base. Added strong acid reacts with some of the in the buffer, and the added strong base reacts with some of the in the buffer.