Faraday constant

In chemistry and physics, the Faraday constant F is the amount of charge (in absolute value) in one mole of electrons or one mole of monovalent (singly charged) ions. Its value is

$F=eN_{\mathrm {A} }=96\,485.339\,9\,\,\mathrm {C/mol} ,$

where N_A is Avogadro's constant and e is the charge of an electron.

The constant F must be carefully distinguished from the unit F (the faraday) which is a unit of capacitance.

The constant and the unit are named after the British physicist Michael Faraday.

Before electrons were discovered and a value for Avogadro's number was known, Faraday discovered (1833) that in electrolysis the amount of charge F necessary to deposit one mole of monovalent ions on an electrode (cations on the cathode, anions on the anode) is always the same, irrespective of the kind of ions. For a long time weighing the amount of silver—which in solution is the cation Ag⁺—deposited during electrolysis was the accepted manner of measuring electric charge and electric current.