Buffer is a solution which resists any change of pH when a small amount of a strong acid or a strong base is added to it. Alternatively, a buffer solution may be defined as a solution whose pH value does not change appreciably upon the addition of small amounts of a strong acid, base and/or water from outside.
Buffer solutions usually consist of a mixture of a weak acid and its salt with a strong base e.g., CH3COOH and CH3COONa, or that of a weak base and its salt with a strong acid e.g., NH4OH and NH4Cl. The solution of any salt of a weak acid and a weak base e.g., ammonium acetate, also shows buffering property. The major application of buffers includes:-
(a) In biochemical systems: pH plays a very significant role in biochemical reactions. For example, the blood in our bodies is buffered at a pH value of 7.36-7.42 due to bicarbonate – carbonic acid buffer. A mere change of 0.2 pH units can cause death. Certain enzymes get activated only at certain definite pH values.
(b) Agriculture: The pH of the soil is very important for having proper crop yield. The soils get buffered due to the presence of salts such as carbonates, bicarbonates, phosphates and organic acids. The choice of fertilizers depends upon pH of the soil.
(c) Industry: Practically all industries use buffers in one process or the other. Major industries, which employ buffers are paper, dyes, ink, paints and drugs industries.
(d) Analytical chemistry: Buffers find extensive use in analytical chemistry, viz., both in qualitative and quantitative analysis. For example, qualitative analysis of Group III and Group IV is done in solutions buffered by NH4Cl + NH4OH. Buffers are used in the removal of interfering radicals such as phosphate, oxalate, borate and fluoride etc. The control of pH is very important in the field of food preservation.