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Question

State Faraday's first law of electrolysis. How is it verified experimentally ?

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Solution

First Law : The mass of a substance liberated at an electrode is directly proportional to the charge passing through the electrolyte.
If an electric current I is passed through an electrolyte for a time t, the amount of charge (q) passed is It.
According to the law, mass of substance liberated (m) is
mq or m=zIt
where Z is a constant for the substance being liberated called as electrochemical equivalent. Its unit is kgC1.
Verification of Faraday's First law of electrolysis: A battery, a rheostat, a key and an ammeter are connected in series to an electrolytic cell. 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
m1m2=I1I2
mt ------------------- (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
m3m4=t1t2
mt -------------- (2)
From relations (1) and (2)
mIt or mq. Thus, the first law is verified.
633669_606149_ans_8ed93941b8ee4f899f1b89fa13eb93ea.png

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