Electrolysis

The value of the constant in the Debye - Huckel -Onsager equation, depends on temperature, charges of the ions, the dielectric constant of the solvent and also the viscosity of the solvent. Here, since we are not given the solvent, we will assume that the solvent is the same for each case. Here, the deciding factor is the charge on the ions. Again, in and , the charges on the ions are the same.

Hence the pair of electrolytes that will possess the same value for the constant (A) will be .

During the electrolysis of brine (aqueous NaCl solution) using inert electrodes, the ions present are:

• At Cathode (Reduction): Na⁺, H₂O molecules
• At Anode (Oxidation): Cl⁻, H₂O molecules

At Cathode (negative electrode):

Reduction potentials:

• Na⁺(aq) + e⁻ → Na(s) (Highly negative potential)
• 2H₂O(l) + 2e⁻ → H₂(g) + 2OH⁻(aq) (Lower negative potential)

H₂ gas is liberated at cathode since reduction of water is more favorable than Na⁺ reduction.

At Anode (positive electrode):

Oxidation potentials:

• 2Cl⁻(aq) → Cl₂(g) + 2e⁻ (Favorable oxidation)
• 2H₂O(l) → O₂(g) + 4H⁺(aq) + 4e⁻ (Less favorable than chloride oxidation in concentrated solutions)

Cl₂ gas is liberated at anode, as oxidation of chloride ions is preferred due to the higher concentration and easier oxidation potential.

Overall reaction for brine electrolysis:

2NaCl(aq) + 2H₂O(l) → Cl₂(g) + H₂(g) + 2NaOH(aq)

Conclusion:

The correct option is: (D) Cl₂ liberates at anode

Correct Answer: Option (D)