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Faraday's Laws of Electrolysis

The mass of substance deposited or dissolved at an electrode is proportional to the electric charge passed through the cell.

Formula

m = \frac{Q \, M}{n \, F} = \frac{I \, t \, M}{n \, F}

Variables

mMass deposited

QCharge (= I t)

MMolar mass

nElectrons per ion

FFaraday constant ≈ 96485 C/mol

Example

Passing 96485 C through molten NaCl deposits 23 g of sodium.

Did You Know?

These laws, from Michael Faraday in 1834, are the basis of electroplating and aluminium smelting.

electrolysis faraday electrochemistry charge law

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More in Scientific Laws & Principles

Law of Conservation of Mass

In a closed system, matter is neither created nor destroyed — the total mass before a reaction equals the total mass after.

Law of Definite Proportions

A given chemical compound always contains its component elements in the same fixed ratio by mass, regardless of source.

Law of Multiple Proportions

When two elements form more than one compound, the masses of one element combining with a fixed mass of the other are in ratios of small whole numbers.

Dalton's Law of Partial Pressures

The total pressure of a mixture of non-reacting gases equals the sum of the partial pressures each gas would exert alone.

Graham's Law of Effusion

The rate at which a gas effuses through a tiny hole is inversely proportional to the square root of its molar mass.

Avogadro's Law

At the same temperature and pressure, equal volumes of gases contain equal numbers of molecules — so volume is proportional to moles.