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Michael Faraday discovered electrolysis

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"On the basis of various experiments conducted, Faraday arrived at two laws of electrolysis, which are as follows:

1. The mass of a substance liberated or deposited at an electrode during electrolysis is directly proportional to the quantity of charge passed through the electrolyte. i.e.,

 ï¿½ q

i.e. m ï¿½ It

or m = ZIt

where m is the mass of the substance, q is the charge (= It, a current I flowing for time t) passing through the electrolyte.

Z is known as the electrochemical equivalent (E.C.E) of the substance.

If q = 1C, then m = Z.

Hence, electrochemical equivalent of a substance is the mass of the substance liberated or deposited in electrolysis by the passage of 1 coulomb of charge. The S.I. Unit of Z is kg/coulomb (kg C-1).

2. When the same amount of charge is made to pass through any number of electrolytes, the masses of the substances liberated or deposited at the electrodes are proportional to their chemical equivalents.

i.e., if m1 and m2 are the masses and E1 and E2 are the chemical equivalents of the two substances, then


Faraday's laws can be explained as follows. Suppose one mole of a substance of mass M and valency p is deposited on an electrode, i.e., an Avogadro number NA of atoms gets deposited. To deposit one atom, a charge pe is required.

Therefore, for a mole (of mass M), the charge required is NA Pe. Then, from the equation m = Zq, we have

M = Z NA pe





The quantity M/p is a constant for a substance and is known as the chemical equivalent E. The E.C.E (Z) of a substance is thus directly proportional to its chemical equivalent (E); this is evident also from the following table" (


Electrolysis is the when electrons are passed through a liquid that has ions




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