Realisation of Mole

The mole, symbol mol, is the SI unit of amount of substance of a specified elementary entity, which may be an atom, molecule, ion, electron, any other particle or a specified group of such particles; its magnitude is set by fixing the numerical value of the Avogadro constant NA to be 6.022 141 29 × 1023 when expressed in the SI unit mol-1. In metrology in chemistry, the realization of mole in all types of chemical entities is done using variety of primary methods of measurements in terms of the amount of substance concentration (mol/m3), amount of substance content (mol/kg) or amount of substance fraction (mol/mol). Three widely used methods to realize the mole are: gravimetric, use of the ideal gas law and electrolysis. At CSIR-NPL, under gas metrology activity, we prepare primary gas standards (especially for greenhouse gases, and criteria pollution gases and particulate matter) by gravimetric method, and realize mole as mol/kg or mol/mol.