Chemical reactions involve interaction of atoms and molecules. A large number of atoms/molecules (approximately $$6.023 \times 10^{23}$$) are present in a few grams of any chemical compound varying with their atomic/molecular masses. To handle such large numbers conveniently, the mole concept was introduced. This concept has implications in diverse areas such as analytical chemistry, biochemistry, electrochemistry and radiochemistry. The following exampleillustrates a typical case, involving chemical/electrochemical reaction, which requires a clear understanding of the mole concept.

A 4.0 molar aqueous solution of NaCl is prepared and 500 mLofthis solution is electrolysed. This leads to the evolution of chlorine gas at one of the electrodes
(atomic mass : Na = 23, Hg = 200; 1 Faraday = 96500 coulombs).