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O Levels Chemistry (5070)•5070/12/O/N/21
Question 20 from 5070/12/O/N/21

Explanation

No redox reaction between Br₂ and Cl⁻

Steps:

  • Recall standard electrode potentials: E°(Cl₂/Cl⁻) = +1.36 V > E°(Br₂/Br⁻) = +1.07 V.
  • Determine oxidizing strength: Cl₂ is stronger oxidant than Br₂, so Br₂ cannot oxidize Cl⁻ to Cl₂.
  • Check for displacement: No reaction as Br₂ is weaker halogen, cannot displace Cl⁻ from NaCl(aq).
  • Conclude: Mixture remains unchanged, no electron transfer.

Why C is correct:

  • Redox requires electron transfer; here, electrode potentials show no spontaneous reaction per Nernst equation.

Why the others are wrong:

  • A: Cl⁻ cannot oxidize Br₂ as Cl⁻ is weaker reducing agent.
  • B: Br₂ cannot oxidize Cl⁻ due to lower reduction potential.
  • D: Na⁺ is spectator ion, not involved in redox.

Final answer: C

Topic: Group VII properties

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