Question
During the chlor-alkali process, which of the following statements is correct regarding the products formed at different electrodes?
This question was previously asked in
RRB ALP 2025 CBT 2 Wiremen Question Paper (28-Jul-2026) (Shift 2)
The correct answer is
Hydrogen gas is released at the cathode and chlorine gas at the anode.
Chlor-Alkali Process: Electrode Products Explained
The chlor-alkali process involves the electrolysis of a concentrated aqueous solution of sodium chloride (brine).
Electrode Reactions
During electrolysis, specific chemical reactions occur at the cathode and anode:
- Cathode (Negative Electrode): Reduction occurs here. Water molecules are reduced to form hydrogen gas (\(H_2\)) and hydroxide ions (\(OH^-\)).
Reaction: \(2H_2O(l) + 2e^- \rightarrow H_2(g) + 2OH^-(aq)\) - Anode (Positive Electrode): Oxidation occurs here. Chloride ions (\(Cl^-\)) are oxidized to form chlorine gas (\(Cl_2\)).
Reaction: \(2Cl^-(aq) \rightarrow Cl_2(g) + 2e^-\)
Overall Products
The key products formed are:
- Hydrogen Gas (\(H_2\)): Released at the cathode.
- Chlorine Gas (\(Cl_2\)): Released at the anode.
- Sodium Hydroxide (\(NaOH\)): Formed in the solution as sodium ions (\(Na^+\)) combine with the hydroxide ions (\(OH^-\)) produced at the cathode. \(Na^+(aq) + OH^-(aq) \rightarrow NaOH(aq)\)
Therefore, hydrogen gas is released at the cathode and chlorine gas at the anode.
This corresponds to Option 1.
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