faraday
Electric chargeexact by definition
The faraday is the charge carried by one mole of elementary charges, exactly 96485.33212... coulombs, being the Avogadro constant times the elementary charge. Since the 2019 revision fixed both of those, the faraday is exact by definition rather than measured. It is electrochemistry's natural lump of charge: one faraday deposits one mole of a singly charged metal ion, half a mole of a divalent one, and liberates half a mole of hydrogen gas.
Watch out: Distinguish the faraday, a quantity of charge, from the farad, a capacitance, and from the Faraday constant, which is this same number expressed as charge per mole. They are related but they are not interchangeable in an equation, and only the farad is an SI unit.
| 1 F | 96,485.332 C |
Named for Michael Faraday, whose two laws of electrolysis in 1833 established that the mass deposited is proportional to the charge passed and to the equivalent weight of the substance. The constant is the bridge between those laws and the mole.