Faraday's Laws of Electrolysis

the quantitative laws of electrolysis that were discovered by M. Faraday in 1833–34. Faraday’s laws express the relationship between the quantity of electricity passed through an electrolyte and the mass and chemical nature, in terms of chemical equivalents, of substances deposited or dissolved at the electrodes.

Faraday’s first law of electrolysis states that the masses m of deposited or dissolved substances are proportional to the quantity of electricity q passed through the electrolyte. The second law states that the masses of different substances deposited or dissolved as a result of the passage of the same quantity of electricity through the electrolyte are proportional to the chemical equivalents A of the substances. It follows from the second law that the same quantity of electricity, called the Faraday constant F, is required for the deposition of the same gram-equivalent weight of different substances. Mathematically, Faraday’s laws may be written as one equation m = (A/F)q = kq, where the coefficient k = A/F is called the electrochemical equivalent.

Both of Faraday’s laws are exact if the ions of the electrolyte carry all the electricity passed through the electrolyte. Deviations from the laws are observed in certain cases; such deviations may be associated with electrochemical side reactions that are not taken into account—for example, the liberation of gaseous hydrogen during the electrodeposition of some metals—or with partial electron conduction—for example, during the electrolysis of certain alloys.