OCR A-Level Chemistry Periodic table, elements and physical chemistry (01), June 2023: Question 12

1 mark · Medium difficulty · Multiple Choice

Identify the correct statement about a lithium-ion cell given the standard electrode potentials of its half-cells.

Practise this question

Question

Multiple choice question 12 showing two half-cell equations for a lithium-ion cell with their standard electrode potentials: Li+ plus e- reversibly forms Li with -3.04V, and Li+ plus CoO2 plus e- reversibly forms LiCoO2 with +1.16V. Four statements A, B, C, and D are given as options, with A stating the cell potential is 2.88 V, B giving a reaction at the positive electrode, C giving the overall cell reaction as Li + CoO2 -> LiCoO2, and D stating the oxidation number of Co changes from +2 to +1. A box for the answer is provided at the bottom left, and [1] mark is indicated at the bottom right.
Question text

12 The equations show the electrode potentials of the half-cells used in a lithium-ion cell.

E ө / V

Li+ + e– Li –3.04

Li+ + CoO + e– LiCoO +1.16

Which statement is correct in a lithium-ion cell?

A The cell potential is 2.88 V.

B The reaction at the positive electrode is: LiCoO Li+ + CoO + e–

C The overall cell reaction is: Li + CoO2 LiCoO2

D The oxidation number of Co changes from +2 to +1.

Your answer [1]

Mark scheme

Show the mark scheme Mark scheme indicating question 12 has the correct answer C, worth 1 mark.

12 C 1 AO2.6

How to answer it

Lithium-Ion Cell Electrode Potentials

OCR A-Level Chemistry • Multiple Choice Question

What this question tests

This question assesses your understanding of electrochemical cells, specifically rechargeable lithium-ion cells. It tests your ability to interpret standard electrode potentials (E&or), determine cell potentials, identify positive and negative electrodes (anode and cathode), deduce overall cell reactions, and calculate oxidation numbers within complex transition metal oxides.

Question 12 Analysis

Evaluating the statements for a lithium-ion cell

✅ Correct Answer: C

The overall cell reaction is: Li + CoO₂ → LiCoO₂

Combining the oxidation of lithium ( Li → Li⁺ + e⁻ ) with the reduction half-equation ( Li⁺ + CoO₂ + e⁻ → LiCoO₂ ) gives the correct overall stoichiometry.

💡 Key Knowledge

  • Cell Potential: Calculated as E(positive) − E(negative) = (+1.16 V) − (−3.04 V) = +4.20 V (making statement A incorrect).
  • Positive Electrode (Cathode): Reduction occurs here ( Li⁺ + CoO₂ + e⁻ → LiCoO₂ ), making statement B incorrect as it shows the reverse process (oxidation).

🧠 Exam Technique

Work through the options systematically by checking standard cell calculations, identifying polarity using the more positive E&or value for reduction, and balancing half-equations before tackling oxidation state changes.

❌ Common Errors

Students frequently miscalculate the cell potential by incorrectly subtracting values or ignoring signs ( +1.16 − (−3.04) = 4.20 V , not 2.88 V). Others struggle with assigning oxidation numbers to cobalt in LiCoO₂ .

Mark Scheme Allocation: 1 mark awarded for selecting option C. (AO2.6 - Applying chemical knowledge to unfamiliar contexts/electrochemical cells).

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), June 2023. QuestionVault is an independent revision resource; questions remain the copyright of the awarding body.