↪ Michael Faraday studied the decomposition of an electrolyte by passing the electric current though them.
↪ He discovered the quantitative relationship between the quantity of electricity passed and the amount of substance deposited at the electrodes.
↪ His results can be expressed in the forms of two laws of electrolysis:
1. Faraday's First Law
↪ According to this law, " The amount of any substance liberated or deposited on the electrode during electrolysis is directly proportional to the quantity of charge passed through the electrolytic solution. "
↪ If m be the mass deposited on or liberated from an electrode and Q be the charge passed through the solution then,
m ∝ Q
or, m = ZQ
⇒m = ZIt where Z = proportionality constant known as electrochemical equivalent
I = Current in ampere
t = time in second
Q = charge passed in coulomb
m = mass of substance deposited
⁕ Electrochemical Equivalent
We have, m = ZIt or Z = m/It
If I = 1ampere, t = 1s, then m = Z. So electrochemical equivalent is defined as the weight of substance deposited or liberated by the passage of one ampere current for 1 second.
↪ Electrochemical equivalent of a substance is defined as the amount of substance deposited or liberated by the passage of one coulomb charge.
⁕ Relationship between ECE and chemical equivalent (E)
↪ 1 Faraday (96500C) charge deposits one gram equivalent of any substance.
↪ Let E be the equivalent weight of a substance then 96500 coulomb deposits E g of a substance.
⇒ 1 coulomb deposits E/96500 g of a substance
By definition, mass deposited or liberated by one coulomb charge is called electrochemical equivalent.
i.e. Z = E/96500
or, m = ZIt
or, m = EIt/96500
or, m = EQ/96500
⁕ One Faraday
↪ Charge carried by one mole of electrons is called one Faraday. It is represented by F and is numerically equal to 96500 coulomb approximately. The exact charge in one Faraday can be calculated as:
1 electron passes 1.602x10-19 coulomb charge
1 mole electrons passes 6.023x1023x1.602x10-19 coulomb of charge
= 96499.9 coulomb
Note: The flow of charge at the rate of 1 coulomb per second is called one ampere current.