First law: The amount of the substance liberated or deposited or dissolved at an electrode during electrolysis of an electrolyte is directly proportional to the quantity of electricity passing through the solution of electrolyte or melt. Mathematically Faraday’s first law is \(m \propto q\) or \(m = eq\) or \(m = ect\), where m is the mass of the substance liberated or deposited or dissolved, q is the quantity of electricity in coulomb, t is the time in seconds, c is the strength of current in amperes and e is the electrochemical equivalent of the ion or metal or molecule deposited or liberated or dissolved at the electrode.
Chemical equivalent of a substance is the amount of substance deposited or liberated or dissolved or had undergone electrode reaction at an electrode during the passage of one Faraday of electricity during the electrolysis of electrolyte solution or melt.
\(\text{Chemical equivalent of an element or ion = }\frac{\text{Atomic weight}}{\text{Valency or charge of the ion}}\)
Second law of Faraday states that if same quantity of electricity is passed through different electrolyte solutions or melts, the amount of the different substances liberated or deposited or dissolved or had undergone reaction at electrode is directly proportional to their chemical equivalents.
\( \displaystyle \frac{W_1}{E_1} = \frac{W_2}{E_2} = \frac{W_3}{E_3} \)
The amount of an ion discharged during electrolysis does not depend on the
Answer & explanation
Correct answer: option 1
The correct answer is Option (1) → resistance of solution
By Faraday’s first law, given in the passage, the mass discharged at an electrode is proportional to the quantity of electricity passed:
\( \displaystyle m=e\,q=e\,c\,t \)
where e is the electrochemical equivalent, c the current in amperes and t the time in seconds. Only these three quantities appear, so the amount discharged depends on them and on nothing else.
Option (1) resistance of solution — Does not decide the amount discharged. Resistance is not in the equation. It only changes the voltage needed to drive a given current; for the same current and time, the same mass is discharged whatever the resistance.
Option (2) time — Decides the amount discharged. At a given current, the charge passed, q = ct, grows with time, and so does m.
Option (3) current strength — Decides the amount discharged. For a given time, a larger current passes more charge and discharges more of the ion.
Option (4) the electrochemical equivalent of the element — Decides the amount discharged. e is the mass discharged by 1 C; it differs from one element to another and fixes how much is discharged per coulomb.