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.
\( \displaystyle \frac{W_1}{E_1} = \frac{W_2}{E_2} = \frac{W_3}{E_3} \)
Consider the following statements about the products of electrolysis.
(A) If the electrode used in electrolysis is inert, for example platinum or gold, it acts only as a source or sink for electrons.
(B) In the electrolysis of molten sodium chloride, sodium metal is obtained at the cathode and chlorine gas at the anode.
(C) Some electrochemical processes, although feasible, are so slow kinetically that an extra potential called overpotential has to be applied, which makes such processes easier to occur.
(D) The products of electrolysis depend on the oxidising and reducing species present in the electrolytic cell and on their standard electrode potentials.
Which of the statements given above are correct? Choose the correct answer from the options given below:
Answer & explanation
Correct answer: option 3
The correct answer is Option (3) → (A), (B) and (D) only
What is formed in electrolysis depends on the substance electrolysed, the type of electrode and the electrode potentials of the species present; a slow process may also need extra voltage.
(A) If the electrode used in electrolysis is inert, for example platinum or gold, it acts only as a source or sink for electrons. — True. An inert electrode does not take part in the reaction; a reactive electrode does, so the products can differ for the two kinds.
(B) In the electrolysis of molten sodium chloride, sodium metal is obtained at the cathode and chlorine gas at the anode. — True. The melt has only one cation and one anion. Na+ is reduced at the cathode and Cl− is oxidised at the anode:
Cathode: \( \displaystyle \ce{Na+ + e^- -> Na} \)
Anode: \( \displaystyle \ce{Cl^- -> 1/2Cl2 + e^-} \)
(C) Some electrochemical processes, although feasible, are so slow kinetically that an extra potential called overpotential has to be applied, which makes such processes easier to occur. — False. The need for an overpotential makes such a process more difficult, not easier: at lower voltages it does not seem to take place at all.
(D) The products of electrolysis depend on the oxidising and reducing species present in the electrolytic cell and on their standard electrode potentials. — True. When several species can react at an electrode, their standard electrode potentials decide which one does.
NCERT (2026-27 edition):
2.5.1 Products of Electrolysis – “Products of electrolysis depend on the nature of material being electrolysed and the type of electrodes being used. If the electrode is inert (e.g., platinum or gold), it does not participate in the chemical reaction and acts only as source or sink for electrons. On the other hand, if the electrode is reactive, it participates in the electrode reaction.” … “The products of electrolysis depend on the different oxidising and reducing species present in the electrolytic cell and their standard electrode potentials. Moreover, some of the electrochemical processes although feasible, are so slow kinetically that at lower voltages these do not seem to take place and extra potential (called overpotential) has to be applied, which makes such process more difficult to occur.”
“For example, if we use molten NaCl, the products of electrolysis are sodium metal and Cl2 gas. Here we have only one cation (Na+) which is reduced at the cathode (Na+ + e– → Na) and one anion (Cl–) which is oxidised at the anode (Cl– → ½Cl2 + e–).”