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Faraday’s Laws of Electrolysis
The relationship between the quantity of electric charge passed through an electrolyte and the amount of the substance deposited at the electrodes was presented by Faraday in 1834, in the form of laws of electrolysis.
(i) Faraday's First Law
When an electric current is passed through an electrolyte, the amount of substance deposited is proportional to the quantity of electric charge passed through the electrolyte.
If W be the mass of the substance deposited by passing Q coulomb of charge, then according to the law, we have the relation:
A coulomb is the quantity of charge when a current of one ampere is passed for one second. Thus, amount of charge in coulombs,
Q = current in amperes × time in seconds
= 1 × t
So W ∝ 1 × t
or W = z × 1 × t
where z is a constant, known as electro-chemical equivalent, and is characteristic of the substance deposited.
When a current of one ampere is passed for one second, i.e., one coulomb (Q = 1), then
W = Z
Thus, electrochemical equivalent can be defined as the mass of the substance deposited by one coulomb of charge or by one ampere of current passed for one second. For example, when a charge of one coulomb is passed through silver nitrate solution, the amount of silver deposited is 0.001118 g. this is the value of electrochemical equivalent of silver.