Buffer solution

Buffer solutions are solutions which resist change in pH, making them very useful for chemical manufacturing and essential for many biochemical processes. Buffer solutions usually consist of either a weak acid and its salt or a weak base and its salt. The resistive action is the result of the equilibrium which is set up between the weak acid and the salt:

HA(aq) <-> H⁺(aq) + A^-(aq)

(Where HA represents the weak acid, H⁺ the hydrogen ion component of the dissolved salt and A^- the anion component of the salt.) Two assumptions are made about the composition of this equilibrium:

1. All the A^- ions result from the salt. This is valid due to the acid's weakness - it supplies very little anions compared to the salt.
2. The HA acid remains unchanged. The high concentration of A^- and H⁺ ions means the equilibrium lies very much to the left.

If an alkali is added to the solution, hydrogen ions mop it up. These ions are regenerated as the equilibrium moves to the right and some of the acid is broken down in to hydrogen ions and anions. If an acid is added, the anions simply combine with the substance and once again pH is restored.

Buffer solutions are necessary to keep the right pH for enzymes in many organisms to work. A lot of enzymes work only under very precise conditions, if the pH strays to far out of the margin the enzymes slow or stop working and the organism dies. Industrially buffer solutions are useful in fermentation processes, and for setting the correct conditions for the dyes used in colouring fabrics.

• For recipes on how to mix buffers see making up solutions