Buffer solutions come in two varieties: acid and alkaline solutions. They resist changes to their pH when small amounts of an alkali or acid are introduced.
Acidic buffers generally consist of a weak acid and an associated salt, usually of the sodium variety. One example of a buffer solution would be mixing ethanoic acid and sodium ethanoate into a solution. The combination of both would produce a pH of 4.76 if the mixture contained equal molar concentrations of the salt and molar.
Alkaline buffers usually consist of a weak base and an associated salt. A typical example of an alkaline buffer solution would be a combination of ammonia and ammonium chloride. The mixture would end up with a pH of 9.25 if it contained equal molar concentrations of both items.
Optimal buffer solutions contain items which remove new hydrogen or hydroxide ions that may be added. Acidic buffer solutions should remove new hydrogen introduced, while alkaline buffers should remove any new hydroxide ions. They should maintain equilibrium to keep the pH balanced.