Question

A current of 9.95 amperes flowing 10 minutes, deposits 3g of metal. An equivalent weight of the metal is:
(A) 12.5
(B) 18.5
(C) 21.5
(D) 48.5

Answer 1

Hint: Determination of equivalent weight of the chemical equivalent by Faraday’s law of electrolysis. The weight of that substance which will combine with or displace the unit weight of hydrogen is known as the equivalent weight of the substance. Since the chemical equivalent of hydrogen is unity and the number of hydrogen atoms is equal to the valence of substance.

Complete step by step answer:
Faraday’s first law of electrolysis:
This law states that the chemical deposition due to the flow of current through an electrolyte which is directly proportional to the quantity of electricity passed through it.
Mass of chemical deposition, $m\alpha Q$
=> $m=ZQ$-- (1)
Where, Q = quantity of electricity in Coulombs, and
Z = constant proportionality which is known as the electrochemical equivalent of a substance
Faraday’s second law of electrolysis:
This law states that when the same quantity of electricity passes through a series of electrolytes, then the mass of substance deposited is proportional to their respective chemical equivalent weights.
Mass of chemical deposition, $m\alpha E$
Where E = equivalent weight
When we consider a series of different electrolytes connected,
${{m}_{1}}:{{m}_{2}}:{{m}_{3}}......={{E}_{1}}:{{E}_{2}}:{{E}_{3}}.....$ -- (2)
From the faraday’ first law of electrolysis,
Q = amperes X second = i X t
Then equation (1) will be, m = Z.i.t -- (3)
Given the mass of metal deposited, m = 3g
Current flow, i=9.95 amperes
Flow time, t = 10mints= 600 seconds

Electrochemical equivalent, Z = $\dfrac{E}{F}$
Where E = equivalent weight of metal =?
F = one faraday = 96500 coulombs
Substitute the above values in equation (3),
3 = $\dfrac{E}{96500} X 9.95 X 600$
E= $\dfrac{3 X 96500}{9.95 X 600}$ = 48.5g
Therefore, the equivalent weight metal is 48.5g.
So, the correct answer is “Option D”.

Note: In chemistry, Faraday’s laws of electrolysis are the quantitative laws used to express magnitudes of electrolytic effects were first described by Michael Faraday. These two laws are applicable for the process of electrolysis of metal salts like metal sulfates in an electrolytic cell.