Faraday’s Laws of Electrolysis

Faraday’s 1st Law of Electrolysis:

Faraday’s first law states that the mass M, of a substance liberated or deposited during electrolysis is directly proportional to the quantity of electricity passing through it.

\( \scriptsize M \propto Q \)

But Q = It

\( \scriptsize M \propto It \)

∴ M = ZIt       

Z is a constant known as the electrochemical equivalent of the substance (e.c.e.)

I = current in amperes, t = time in seconds

The electrochemical equivalent (e.c.e.) of a substance is the mass of the substance deposited by one coulomb of electricity during electrolysis. Unit = gC^-1

Example 9.5.1:

Find the mass of silver deposited on the cathodeA cathode is the electrode from which a conventional current leaves the electrolyte. It is the negative part of the cell where reduction takes place. More of a silver voltameter if a current of 0.7 A is passed through it for 25 minutes. (E.c.e of silver = 4.5 × 10^-4 gC^-1 )

Solution

From Faraday’s first law 

M = ZIt        

= 4.5 × 10^-4 × 0.7 × 25 × 60

= 0.473 g

Example 9.5.2:

What mass of copper will be deposited by a current of 0.53 A in 15