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
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.