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Faraday’s Laws of Electrolysis

First Law: The mass of a substance liberated by electrolysis is directly proportional to the quantity of electricity passed through the electrolyte.
If m kg of substance is liberated in electrolysis by Q coulomb of electricity passed through the electrolyte, m ∞ Q.
    Or        m = zQ                                    ... (1)
Here, z is a constant called the electro chemical equivalent of the substance. If Q = 1 C, then z = m.
The electro chemical equivalent (ece) of an element is defined as the mass of the element in kilogram liberated of passing one coulomb of electricity through its electrolyte. It is expressed in kilogram per coulomb.

Second law: The masses of different substances liberated by passing the same quantity of electricity through their electrolytes are directly proportional to their equivalent weights.
Thus if masses m1, m2, m3 of the three different elements of equivalent weights E1, E2, E3 are liberated by the passage of the same quantity of electricity, we have
        m1 : m2 :  m3 = E1 : E2 : E3
or        m1 / E1 = m2 /E2 = m3/E3  = a constant                         … (2)

If Q is the quantity of electricity passed through all voltammeters, then
        m1 = z1Q,     m2 = z2Q,             and             m3 = z3Q
Here, z1, z2 and z3 are the respective electrochemical equivalents.
Hence Eq. (3) becomes
        z1/E1 = z2/E2 = z3/E3 = constant                            … (3)
The Faraday, Eq. (3) may be written as
        E1/z1 = E2 /z2 = E3/z3 = constant                            … (4)

When the ratio Equivalent weight/ece is called for an element, it is found to be equal to nearly 96,500 C is all cases. This means that in order to liberate a gram equivalent of an element (one chemical equivalent of an element) by electrolysis, the quantity of electricity needed is 96, 500 C. This quantity of electricity is called one faraday. Thus
        1faraday = 96,500 coulomb.

Thus a Faraday may be defined as the quantity of charge necessary to liberate one gram equivalent of any elements.

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