Question

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

Answer 1

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 $\left(q\right)$ passed is $It$.
According to the law, mass of substance liberated $\left(m\right)$ is
$m\propto q$ or $m=zIt$
where $Z$ is a constant for the substance being liberated called as electrochemical equivalent. Its unit is $kg{C}^{-1}$.
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 $I_1$ 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 $m_1$ of the substance deposited is obtained.
The cathode is reinserted in the cell and a different current $I_2$ is passed for the same time $t$. The mass $m_2$ of the deposit is obtained. It is found that
$\frac{m_1}{m_2}=\frac{I_1}{I_2}$
$\therefore m\propto t$ ------------------- (1)
The experiment is repeated for same current $I$ but for different times $t_1$ and $t_2$. If the masses of the deposits are $m_3$ and $m_4$ respectively, it is found that
$\frac{m_3}{m_4}=\frac{t_1}{t_2}$
$m\propto t$ -------------- (2)
From relations (1) and (2)
$m\propto It$ or $m\propto q$. Thus, the first law is verified.