Faraday's law of electrolysis

Statement

m = (A·I·t) / (n·F) — the mass deposited or dissolved at an electrode is proportional to the charge Q = I·t that passed, where A is the molar mass, n the valence, and F = 96485 C/mol the Faraday constant.

Why is it true?

Each ion carries an integer number of elementary charges e, so measuring total charge (Q = It) is equivalent to counting ions — which is how Faraday "counted atoms" with an ammeter in 1834, decades before the electron was discovered.

The same law gives an electrochemical measure of Avogadro's number: F = N_A·e.

Applications

Electroplating (gold, silver, chrome), copper and aluminum refining, lithium-ion charging, hydrogen production by water electrolysis, underground-pipeline cathodic protection.

Topics that use this theorem

Related theorems

Step-by-step proofs