Faradays’s Laws of Electrolysis

Michael Faraday studied the decomposition of electrolyte by passing an electric current through them. He discovered quantitative relation between the quantity of electricity supplied and the amount of substance deposited at the electrodes and gave two laws:

Faraday’s first law of electrolysis: It states that, “The amount of mass of substance deposited at the respective electrode is directly proportional to the quantity of charged passed.”

i.e., m ∝ Q

or, m = ZQ……..(i)

or, m = ZIt………(ii)

where,

m = mass deposited in electrodes

Q = quantity of charge passed

Z = electrochemical equivalent (ECE)

When 1 coulomb charged is passed (i.e.,Q = 1), then equation (i) becomes,

m = Z.1

m = Z……..(ii)

Thus electrochemical equivalent can be defined as the amount of mass of substance deposited at the respective electrodes when one coulomb of charge is passed through the solution. It is also related with Faraday’s constant as:

Z = E/F

or, F = E/Z

Faraday’s Second Law of electrolysis: It states that,”When same quantity of electricity is passed through the solution of different electrolytes, the amount of different substance deposited at respective electrodes is directly proportional to their electrochemical equivalent.”

Mathematically,

m ∝ E

Where,

W is the weight of substance deposited and E is the electrochemical equivalent.

The above relation can be written as:

m= Constant × E

therefore, m/E = Constant …….(i)

When same quantity of electricity is passed through different electrolytes, then equation (ii) can be written as:

m1/E1 = m2/E2 = Constant……(ii)

This is the mathematical representation of Faraday’s second law of electrolysis.

 

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