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9.4 Faraday’s Laws of Electrolysis

Faraday’s Laws of Electrolysis give the relationship between the amount of material liberated at the electrode and the amount of electric energy that is passed through the electrolyte.

First Law of Electrolysis : It states that the amount of any substance that is liberated at an electrode during electrolysis is directly proportional to the quantity of electricity passed through the electrolyte.

W µ Q \ Q = I ´ t

\ W µ I ´ t

Therefore, W = Z ´ I ´ t

Where W = Weight of substance deposited or liberated at the electrode

Z = is the constant (electrochemical equivalent)

I = current strength in ampere

t = time in second

Second Law of Electrolysis : It states that when the same amount of electricity is passed through different electrolytes, the amount of different substances deposited or liberated are directly proportional to the equivalent weight of the substances. Consider two cells connected in a series containing copper sulfate and silver nitrate and if the electric current passes through both the cells then,

weight of silver deposited µ Equivalent weight of silver

and weight of copper deposited µ Equivalent weight of copper

\WAg EAg

WCu = ECu

The basic unit of electrical charge is called Faraday which is defined as the charge on one mole of electrons. Electrolysis of sodium iodide solution to find out Faraday can be given as follows :

Na (l) + e- ® Na (l) Reduction

2 I - (l) ® I2 (s) + 2e- Oxidation

Net reaction 2Na(l) + 2I-(l) ® 2Na(l) + I2 (s) (Redox)

The passage of 1 Faraday of charge will produce 1 mole of Sodium metal and 2 Faraday of charge will produce 1 mole of Iodine.

The passage of 2 Faraday of charge will give 2 moles of sodium metal and 1 mole of iodine.



9.1 Introduction
9.2 Electrolytic Cell
9.3 Electrolytes
9.4 Faraday's Law of Electrolysis
9.5 Electrochemical Cell
9.6 Electrode Potential

Chapter 10

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