Lesson 3 : Water, pH and Buffers


A buffer solution is an aqueous solution consisting of a mixture of a weak acid and its conjugate base or a weak base and its conjugate acid. It has the property that the pH of the solution changes very little when a small amount of acid or base is added to it. Buffer solutions are used as a means of keeping pH at a nearly constant value in a wide variety of chemical applications (Buffers )


Their resistance to changes in pH makes buffer solutions very useful for chemical manufacturing and essential for many biochemical processes. The ideal buffer for a particular pH has a pKa (The Ka value is a value used to describe the tendency of compounds or ions to dissociate. The Ka value is also called the dissociation constant, the ionisation constant and the acid constant.) equal to that pH, since such a solution has maximum buffer capacity.( pKa and Ka )

Buffer solutions are necessary to keep the correct pH for enzymes in many organisms to work. Many enzymes work only under very precise conditions; if the pH strays too far out of the margin, the enzymes slow or stop working and can denature, thus permanently disabling its catalytic activity

Industrially, buffer solutions are used in fermentation processes and in setting the correct conditions for dyes used in colouring fabrics. They are also used in chemical analysis and calibration of pH meters.

Majority of biological samples that are used in research are made in buffers specially PBS (phosphate buffer saline) at pH 7.4.

Useful buffer mixtures


pH range

HCl, Sodium citrate

1 - 5

Citric acid, Sodium citrate

2.5 - 5.6

Acetic acid, Sodium acetate

3.7 - 5.6

Na2HPO4, NaH2PO4

6 - 9

Borax, Sodium hydroxide

9.2 - 11

A mixture containing citric acid, potassium dihydrogen phosphate, boric acid, and diethyl barbituric acid can be made to cover the pH range 2.6 to 12

Last modified: Tuesday, 17 January 2012, 6:13 AM