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MCQEasyJEE 2023Faraday's Laws of Electrolysis

JEE Chemistry 2023 Question with Solution

The product, which is not obtained during the electrolysis of brine solution, is:

  • A

    HCl

  • B

    NaOH\text{OH}

  • C

    Cl2\text{Cl}_2

  • D

    H2\text{H}_2

Answer

Correct answer:A

Step-by-step solution

Standard Method

Given: Brine is a concentrated aqueous solution of NaCl\text{NaCl}.

Find: The product that is not obtained during electrolysis of brine solution.

During electrolysis of brine, water is reduced at the cathode and chloride ions are oxidized at the anode.

At the cathode:

2H2O(l)+2e−→H2(g)+2OH−(aq)2\text{H}_2\text{O(l)} + 2e^- \rightarrow \text{H}_2\text{(g)} + 2\text{OH}^-\text{(aq)}

At the anode:

2Cl−(aq)→Cl2(g)+2e−2\text{Cl}^-\text{(aq)} \rightarrow \text{Cl}_2\text{(g)} + 2e^-

Overall reaction:

2NaCl(aq)+2H2O(l)→H2(g)+Cl2(g)+2NaOH(aq)2\text{NaCl(aq)} + 2\text{H}_2\text{O(l)} \rightarrow \text{H}_2\text{(g)} + \text{Cl}_2\text{(g)} + 2\text{NaOH(aq)}

Therefore, the products obtained are H2\text{H}_2, Cl2\text{Cl}_2, and NaOH\text{NaOH}. HCl\text{HCl} is not formed, so the correct option is A.

Common mistakes

  • Confusing the products of electrolysis of brine with the reactants present in solution. Cl−\text{Cl}^- ions produce Cl2\text{Cl}_2 at the anode, not HCl\text{HCl}. Always write the electrode reactions before choosing the product.

  • Assuming sodium metal forms at the cathode. In aqueous brine, water is preferentially reduced, giving H2\text{H}_2 and OH−\text{OH}^-. Check whether the medium is aqueous before predicting discharge products.

  • Forgetting to combine Na+\text{Na}^+ with OH−\text{OH}^- to identify NaOH\text{NaOH} in the final products. The net products must be inferred from the overall reaction, not only from isolated half-reactions.

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