OCR A-Level Chemistry Periodic table, elements and physical chemistry (01), June 2019: Question 2

1 mark · Medium difficulty · Multiple Choice

Identify the correct statement regarding the redox reactions of halogens and halide ions from multiple choice options

Practise this question

Question

Multiple choice question 2 asking which statement about the reactions of halogens with halide ions is correct. Option A is I2(aq) can oxidise Br-(aq), option B is Cl2(aq) can reduce Br-(aq), option C is Br-(aq) can reduce Cl2(aq), and option D is Cl-(aq) can oxidise I2(aq). An answer box is provided at the bottom with a [1] mark allocation.
Question text

2 Which statement about the reactions of halogens with halide ions is correct?

A I (aq) can oxidise Br−(aq).

B Cl (aq) can reduce Br−(aq).

C Br−(aq) can reduce Cl (aq).

D Cl −(aq) can oxidise I (aq).

Your answer [1]

Mark scheme

Show the mark scheme Mark scheme showing the correct answer for question 2 is C.

2 C 1 AO1.2

How to answer it

Reactivity and Redox Trends of Group 7 Halogens

What this question tests

This question assesses your understanding of trends in oxidising ability down Group 7 (the halogens) and the displacement reactions between halogens and halide ions. You must correctly apply definitions of oxidising and reducing agents to specific chemical species.

Question 2 (Multiple Choice)

Halogen Displacement and Redox

✅ Correct Answer: C

Br⁻(aq) can reduce Cl₂(aq) .

💡 Key Knowledge

  • Oxidising power: Decreases down Group 7 (Cl₂ > Br₂ > I₂).
  • Reducing power: Increases down Group 7 (I⁻ > Br⁻ > Cl⁻).
  • A more reactive halogen will displace a less reactive halide from solution.
  • Halogens act as oxidising agents (they get reduced by gaining electrons). Halides act as reducing agents (they get oxidised by losing electrons).

🧠 Exam Technique

  • Break down each statement carefully: identify the species losing or gaining electrons.
  • Remember the mnemonic: OIL RIG (Oxidation Is Loss, Reduction Is Gain of electrons).
  • Check the reactivity trend: Chlorine is a stronger oxidising agent than bromine, and bromine is stronger than iodine. Therefore, Cl₂ can oxidise Br⁻, meaning Br⁻ reduces Cl₂.

❌ Common Errors

  • Option A: Incorrect because iodine ( I₂ ) is a weaker oxidising agent than bromine, so it cannot oxidise bromide ions ( Br⁻ ).
  • Option B: Incorrect identification of roles; chlorine is the oxidising agent, not the species being reduced by bromide.
  • Option D: Chloride ions ( Cl⁻ ) are very weak reducing agents and cannot oxidise iodine ( I₂ ).
Mark Scheme Allocation: 1 mark awarded for selecting C (AO1.2 - Demonstrating knowledge and understanding of scientific ideas).

Topics

Module 3: Periodic table and energy · 3.1 The periodic table

Question and mark scheme from the OCR A-Level Chemistry examination, Periodic table, elements and physical chemistry (01), June 2019. QuestionVault is an independent revision resource; questions remain the copyright of the awarding body.