Which of the following products is NOT formed when electricity is passed through an aqueous solution of sodium chloride? 

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RRB Technician Grade III Official Paper (Held On: 29 Dec, 2024 Shift 1)
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  1. Hydrogen gas 
  2. Sodium hydroxide 
  3. Chlorine gas  
  4. Oxygen gas  

Answer (Detailed Solution Below)

Option 4 : Oxygen gas  
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Detailed Solution

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The correct answer is Oxygen gas.

Key Points

  • When electricity is passed through an aqueous solution of sodium chloride (brine), the main products formed are hydrogen gas, chlorine gas, and sodium hydroxide.
  • Hydrogen gas is produced at the cathode due to the reduction of water molecules.
  • Chlorine gas is generated at the anode by the oxidation of chloride ions.
  • Sodium hydroxide is formed in the solution as a result of the ions remaining after the electrolysis process.
  • Oxygen gas is not produced in this process as the primary reactions involve the decomposition of water and chloride ions, not oxygen.

Additional Information

  • Electrolysis:
    • Electrolysis is a chemical process that uses electric current to drive a non-spontaneous chemical reaction.
    • In the electrolysis of brine, the solution conducts electricity due to the presence of ions.
  • Brine Solution:
    • Brine is a high-concentration solution of salt (sodium chloride) in water.
    • It is commonly used in the chlor-alkali industry for the production of chlorine, hydrogen, and sodium hydroxide.
  • Cathode and Anode Reactions:
    • At the cathode: 2H2O + 2e- → H2 + 2OH-
    • At the anode: 2Cl- → Cl2 + 2e-
  • Industrial Applications:
    • The products of brine electrolysis are used in various industries: chlorine for disinfectants and PVC, hydrogen for fuel, and sodium hydroxide for soap and paper manufacturing.
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