A solution of a weak acid and its salt (or a solution of a weak base and its salt)
is called a buffer solution or a buffer. Buffer solutions are able to resist a
change in pH when small amounts of acid or base are added. A solution of
acetic acid sodium acetate is an example of a buffer that consists of a weak
acid and its salt. For an example of a buffer that consists of a weak base and
its salt, there is a solution of ammonia and ammonium chloride.