# Electrochemical Equivalent (z)

According to Faraday’s first law of electrolysis,

m = z q

or, z = m / q,

where *q = 1C*, then

z = m

Hence, the electrochemical equivalent is the mass of ions deposited or liberated on an electrode during the electrolysis, where 1C of charge is passed through it.

# Chemical Equivalent (E)

Chemical equivalent is defined as the atomic weight expressed in gram per unit valency.

E = atomic weight / Valency

It’s also known as gram equivalent weight of the substance.

# Relation between E and z

Let us consider ‘q’ be the amount of charge which is passed through the 2 electrolytes whose chemical equivalence are E_{1} and E_{2}, and their respective electrochemical equivalence are z_{1} and z_{1}. If m_{1} and m_{2} are the masses of ions deposited or liberated on an electrode in 2 voltameters, then from first law of Faraday,

m

_{1}= z_{1}q and m_{2}= z_{2}qor, m

_{1}/ m_{2}= z_{1}/ z_{2 }——–(i)

And, from Faraday’s second law,

m

_{1}/ E_{1}= m_{2}/ E_{2}or, m

_{1}/ m_{2}= E_{1}/ E_{2 }——–(ii)

Now, from equation (i) and (ii), We get,

E

_{1}/ E_{2}= z_{1}/ z_{2}i.e. E

_{1}/ z_{1}= E2 / z_{2}i.e. E / z = constant

i.e. E / z = F

i.e.

E = F z,

where ‘F’ is a constant called Faraday’s constant.

# Faraday’s Constant

According to first law of electrolysis,

m = z q

z = m / q

But, F = E / z = E * q /m

If E = m, then

F = q

Therefore, Faraday’s constant can be defined as the amount of charge required to liberate a gram equivalent of a substance during the electrolysis.

Example,

For copper,

Chemical equivalent (E) = 31.5 gm

Electrochemical equivalent, e.c.e. (z) = 0.000329 gm/C

We know that,

F = E / z

or, F = 31.5 / 0.000329

∴ F = 96500C