The solution which resists changes in the hydrogen ion concentration on the addition of small amount of acid or base is known as buffer solution.
Many medical and cosmetic formulations need a definite pH for their formulation and use. Such solutions are called buffer solutions. These solutions maintain a fairly constant pH value and are known to posses reserve acidity and reserve basicity in them.
For example: human blood is an excellent example of natural buffer solution. Blood maintains its pH value around 7.35 inspite of a wide variety of foods we take.
Buffer solutions are of two types:
a) Acidic buffer
b) Basic buffer
Acidic buffer solution contains equimolar quantities of a weak acid and its salt with strong base. For example: an acetic acid, CH3COOH and sodium acetate I.e. CH3COONa. A solution containing equimolar quantities of acetic acid and sodium acetate maintains its pH value around 4.74.
Basic buffer solution contains equimolar quantities of a weak base and its salt with strong acid. For example: ammonium hydroxide i.e. NH4OH and ammonium chloride I.e. NH4Cl. A solution containing equimolar quantities of ammonium hydroxide and ammonium chloride maintains its pH value around 9.25.