A solution in which the pH remains
reasonably constant when acids or
alkalis are added to it; i.e. it acts as a buffer
against (small) changes in pH. Buffer solutions
generally contain a weak acid and
one of its salts derived from a strong base;
e.g. a solution of ethanoic acid and sodium
ethanoate. If an acid is added, the H+ reacts
with the ethanoate ion (from dissociated
sodium ethanoate) to form undissociated
ethanoic acid; if a base is added the OH–
reacts with the ethanoic acid to form water
and the ethanoate ion. The effectiveness of
the buffering action is determined by the
concentrations of the acid–anion pair:
K = [H+][CH3COO–]/[CH3COOH]
where K is the dissociation constant.
Phosphate, oxalate, tartrate, borate,
and carbonate systems can also be used for
buffer solutions.
