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Faraday’s Second Law of Electrolysis

The Faraday’s second law of electrolysis is defined as,

“The masses of different substances, liberated or dissolved by the same amount of electricity are proportional to their equivalent masses.”

Thus, when the same quantity of electricity is passed through a number of electrolytic solutions connected in series then the masses of the different materials liberated or dissolved at the respective electrodes are in the ratio of their equivalent masses.

For example, when the same current is passed through the solutions of  sulphuric acid (H2SO4), copper sulphate (CuSO4), and silver nitrate (AgNO3) for the same period of time then:

  • Mass of copper deposited/Mass of silver deposited = Equivalent mass of copper/Equivalent mass of silver and,
  • Mass of copper deposited/Mass of hydrogen gas liberated =Equivalent mass of copper/Equivalent mass of hydrogen

Then, according to the second law of electrolysis, “The same quantity of electricity will produce or dissolve chemically equivalent amounts of all the substances.”

Therefore, the same quantity of electricity is required to liberate or dissolve one equivalent of any material during electrolysis. This quantity of electricity is called Faraday (F). One Faraday is equal to 96487 coulomb per mole of electronic charges. For the sake of convenience, we generally use a value 96500 C mol–1 for the Faraday constant (F).

So, 1 Faraday = 1 F= Electrical charge carried by one mole of electrons
1 F= Charge on an electron × Avogadro’s number


1 F=e–× NA= (1.602 × 10–19C) × (6.02 × 1023mol–1),1 F= 96488 C mol–1

The Faraday’s laws of electrolysis are applicable only,

(i) When the whole conduction is electrolytic in nature, i.e., the current is carried only by the ions only.

(ii) No other side-reaction takes place after the electrode reaction has taken place.

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