During electrolysis, chemical reactions occur at the electrodes. M. Faraday (1833) studied the quantitative aspects of electrolysis, and postulated two famous laws named after him. These laws are described below.

Faraday’s First Law of Electrolysis

Faraday’s first law of electrolysis may be defined as follows:

“The mass of any substance deposited or dissolved at any electrode during electrolysis is directly proportional to the quantity of electricity passed through the solution.” 

It may also be defined as, “the amount of any substance involved in a reaction at an electrode is directly proportional to the quantity of electricity passed through the solution.”

Mathematically, if Wg of any material gets deposited or dissolved when Qcoulombs of electricity is passed, then

W∝Q
But, Q=I× t
Therefore,      W∝I t
or, W=Z I t …

where, Z is the electrochemical equivalentof the substance.

If, I= 1 unit (say, 1 ampere) and t= 1 unit (say, 1 second). Then, Z=W i.e., the electrochemical equivalent of a substance is equal to the mass of the substance deposited or dissolved, when a current of one ampere is passed for one second.

Primary product of electrolysis.The material formed directly by the current at the electrode surface during electrolysis is called primary product of electrolysis. For example, for the electrode reaction,

Cu2+ + 2e– → Cu,

 copper (Cu) is the primary product.

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