Applications of buffer solutions

Buffer solutions are very useful in a wide range of industrial processes. They are also vital to many biochemical systems.

Manufacture of shampoos

In the manufacture of shampoos, a citric acid/citrate buffer is added to the solution to maintain the pH of the shampoo at a slightly acidic level (about pH = 5.5).

C_6H_8O_7\rightleftharpoons 3H^++C_6H_5O_7^{\; \: 3-}

The outer most region of a fibre of hair is called the cuticle, which acts as a barrier to the entry of harmful chemicals into the inner regions of the hair. The cuticle consists of superimposed layers of cells linked by cysteine molecules. When the disulphide bonds of these cysteine linkages are disrupted by hydroxyl molecules (see diagram below), the structure of the cuticle changes, opening up the cuticle and allowing entry of undesirable chemicals into the hair. Since the pH of an unbuffered shampoo increases when we soap our hair with water (due to the hydrolysis of soap), a buffer is added during the manufacturing process to maintain an acidic pH.

Fermentation of alcoholic beverages

During fermentation of alcoholic beverages, yeast enzymes convert sugars to alcohols:

C_6H_{12}O_6\rightarrow 2C_2H_5OH+2CO_2

These enzymes function optimally within a certain pH range, usually 4 < pH < 7. If the solution is either too acidic or too alkaline, the enzymes are inhibited and/or yeast may not survive.

Carbon dioxide formed during fermentation acidifies the solution via the following equilibria:

CO_2+H_2O\rightleftharpoons H_2CO_3\rightleftharpoons H^++HCO_3^{\; \: -}

Therefore, the change in pH during fermentation can be resisted by the addition of bicarbonate salts or using a phosphoric acid/phosphate buffer.


Biological buffers

Finally, human biological fluids require constant pH levels for biochemical processes to function properly.

The pH of blood (pH = 7.4) is maintained by a carbonic acid/bicarbonate buffer, while the pH of intracellular fluid is stabilised by the carbonic acid/bicarbonate buffer, protein buffers and the dihydrogen phosphate/hydrogen phosphate buffer.

H_2PO_4^{\; \: -}\rightleftharpoons H^++HPO_4^{\; \: 2-}


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