OCR A-Level Chemistry Periodic table, elements and physical chemistry (01), November 2021: Question 12

1 mark · Easy difficulty · Multiple Choice

Identify the strongest oxidising agent given two redox systems with their standard electrode potentials.

Practise this question

Question

Multiple choice question 12 presents two redox systems: Fe2+(aq) + 2e- reversible arrow Fe(s) with E-theta = -0.44 V, and Cu2+(aq) + 2e- reversible arrow Cu(s) with E-theta = +0.34 V. It asks which species in the two redox systems is the strongest oxidising agent, with options A Fe2+(aq), B Fe(s), C Cu2+(aq), and D Cu(s).
Question text

12 Two redox systems are shown below.

Fe2+(aq) + 2e– Fe(s) E –o = –0.44 V

Cu2+(aq) + 2e– Cu(s) E –o = +0.34 V

Which species in the two redox systems is the strongest oxidising agent?

A Fe2+(aq)

B Fe(s)

C Cu2+(aq)

D Cu(s)

Your answer [1]

Mark scheme

Show the mark scheme The mark scheme indicates the correct answer is C for question 12, awarding 1 mark under AO1.2.

12 C 1 AO1.2

How to answer it

Identifying the Strongest Oxidising Agent from Electrode Potentials

What this question tests

This question assesses your understanding of electrode potentials (E-theta values) and how they correlate with the chemical reactivity of species. Specifically, it tests your ability to link the magnitude and sign of standard cell potentials to the strength of oxidising and reducing agents.

Question 12 Overview

Multiple-Choice Analysis

✅ Correct Answer: C

Cu²⁺(aq) is the correct option. The species with the most positive standard electrode potential is the strongest oxidising agent because it has the greatest tendency to accept electrons and undergo reduction.

💡 Key Knowledge

  • Oxidising agents accept electrons (they get reduced).
  • The more positive (or less negative) the E-theta value, the greater the tendency for the forward reduction reaction to occur.
  • Oxidising agents are always found on the left-hand side of the half-equations.

🧠 Exam Technique

Read multiple-choice questions carefully to distinguish between left-hand side species (oxidising agents/ions) and right-hand side species (reducing agents/metals). Look straight at the E-theta values: the highest value automatically corresponds to the strongest oxidising agent.

❌ Common Errors

  • Choosing Cu(s) (option D) by confusing oxidising agents with reducing agents. Cu(s) is on the right and acts as a reducing agent.
  • Selecting negative E-theta species ( Fe²⁺ or Fe ) thinking "strongest" correlates with the extremes of the number line regardless of sign.
Mark Scheme Allocation: 1 mark awarded for selecting C (AO1.2 - Demonstrate knowledge and understanding of scientific ideas).

Topics

Module 5: Physical chemistry and transition elements · 5.2 Energy

Question and mark scheme from the OCR A-Level Chemistry examination, Periodic table, elements and physical chemistry (01), November 2021. QuestionVault is an independent revision resource; questions remain the copyright of the awarding body.