QS Study

Verification of Faraday’s first law of electrolysis

First Law: A battery, a rheostat, a key and an ammeter are connected in series to an electrolytic cell (Figure). The cathode is cleaned, dried, weighed and then inserted in the cell. A current I1 is passed for a time t. The current is measured by the ammeter. The cathode is taken out, washed, dried and weighed again. Hence the mass m1 of the substance deposited is obtained.


The cathode is reinserted in the cell and a different current I2 is passed for the same time t. The mass m2 of the deposit is obtained. It is found that

m1/m2 = I1/I2

so, m α I … … … (1)

The experiment is repeated for same current I but for different times t1 and t2. If the masses of the deposits are m3 and m4 respectively, it is found that

m3/ m4 = t1/ t2

so, m α t … … … (2)

From relations (1) and (2)

m α It or m α q Thus, the first law is verified.