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.
\( \displaystyle \frac{W_1}{E_1} = \frac{W_2}{E_2} = \frac{W_3}{E_3} \)
A steady current of 0.80 A is passed through an electrolytic cell for 10 minutes. How many electrons flow through the circuit in this time? (Charge on one electron = 1.6 × 10−19 C)
Answer & explanation
Correct answer: option 2
The correct answer is Option (2) → 3.0 × 1021
The quantity of electricity passed is Q = It, with I in ampere and t in seconds. Each electron carries 1.6 × 10−19 C, so the number of electrons is the total charge divided by the charge on one electron.
\( \displaystyle t = 10 \times 60\ \mathrm{s} = 600\ \mathrm{s} \)
\( \displaystyle Q = It = 0.80\ \mathrm{A} \times 600\ \mathrm{s} = 480\ \mathrm{C} \)
\( \displaystyle N = \frac{Q}{e} = \frac{480\ \mathrm{C}}{1.6 \times 10^{-19}\ \mathrm{C}} = 3.0 \times 10^{21} \)
NCERT (2026-27 edition):
2.5 Electrolytic Cells and Electrolysis – “…we now have constant current (I) sources available and the quantity of electricity Q, passed is given by Q = It. Q is in coulombs when I is in ampere and t is in second.”
“We know that charge on one electron is equal to 1.6021 × 10–19 C.”