Faraday Constant

A mole of electrons is given a special name: 1 Faraday. The charge of 1 mole of electrons is called the Faraday Constant, F.

It is calculated by multiplying the charge of one electron by the Avogadro constant.

1 Faraday = 9.648 70 x 10⁴, coulombs/faraday (C mol^-1).

In electrolysis, Michael Faraday in 1832 - 1833 discovered the relationship between the charge and the quantity of matter liberated in an electrode reaction. He did not know about partial reactions at electrodes, electrons, or a unit (to be) named after him. He did know something about atomic and molecular masses. His results are summarised in two laws, now famous as Faraday's laws.

The mass of a substance produced or consumed is proportional to the quantity of charge (current x time) that has passed through the circuit.
The number of faradays that must pass through a circuit when one mole of a substance is produced or consumed is a whole number.

What the whole number is depends on the substance and the reaction. For example:

2 faradays produce 1 mol of H₂:
2H⁺ + 2e^- ® H₂

1 faraday produces 1 mol of Ag:
Ag⁺ + e^- ® Ag

3 faradays produce 1 mol of Al:
Al³⁺ + 3e^- ® Al

That one mole of atoms or molecules always requires an integral number of faradays suggests a once novel but now familiar idea: the existence of a natural unit of charge, the charge of an electron.