What is Faraday's law of Electrolysis?

Faraday's law of electrolysis

The relationship between the amount of electric charge passing through an electrolyte and the amount of substance deposited at the electrode was introduced by Faraday in 1834 as the laws of electrolysis.

1. first law

The mass of the substance deposited or liberated at any electrode is directly proportional to the amount of charge passed"

Let this proportionality be called w = zq.  can be made in equality by

Where z is the proportionality constant called the electrochemical equivalent.  It is the mass of matter in grams that is deposited or released by passing a coulomb of charge.

2. Second Law

The mass of a substance that is deposited or liberated at an electrode when a certain amount of charge is passed is directly proportional to its chemical equivalent mass".

that is w a E where w is the mass of the substance in grams while E is its chemical equivalent weight per gram equivalent.

This law can be explained as follows.

Consider three reactions, such as:

 Na+ + E– → Na

 Cu2+ + 2e–→ Cu

 Al3+ + 3e– → Al

Assume that these three reactions are taking place in three separate electrolytic cells connected in series.

Electrolytic cells
Electrolytic cells

Example: When x mole electrons are passed through three cells, the mass of the deposited Na, Cu and Al are 23x g, 31.75x g and 9x g respectively.

We can see that 23, 31.75 and 9 gm/eq are the chemical equivalent weights of the three elements.

w = moles of electrons \ times E

charge of 1 mole of electrons= 1.6 \times10–19 \times6.023 x 1023 96500 C


This charge is called 1 Faraday.

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