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IGCSE · Practice questions · Redox

Follow the electrons.

Six original Cambridge-style questions on redox: gain and loss of oxygen, electron transfer, oxidation numbers, and oxidising and reducing agents.

Original questions All questions on this page are original work, written in the Cambridge IGCSE style. They are not from past papers. They test the same concepts and skills the syllabus rewards.
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OIL RIG.

01
Recall
[2 marks]

In the blast furnace, Fe2O3 + 3CO → 2Fe + 3CO2. Identify the substance oxidised and the substance reduced, explaining in terms of oxygen.

  • Carbon monoxide is oxidised: it gains oxygen to form carbon dioxide. ✓
  • Iron(III) oxide is reduced: it loses oxygen to form iron. ✓
02
Recall
[2 marks]

Give the formulae of (a) copper(II) oxide and (b) iron(II) chloride, and state what the Roman numerals show.

  • (a) CuO; (b) FeCl2. ✓
  • The Roman numeral gives the oxidation number (the charge on the metal ion): +2 in both. ✓
03
Analysis
[3 marks]

(Extended) Magnesium reacts with copper(II) sulfate solution: Mg + Cu2+ → Mg2+ + Cu. In terms of electrons, state which species is oxidised and which is reduced, and name the reducing agent.

  • Magnesium is oxidised: it loses two electrons (0 → +2). ✓
  • Cu2+ is reduced: it gains two electrons (+2 → 0). ✓
  • Magnesium is the reducing agent. ✓
04
Analysis
[2 marks]

(Extended) Use oxidation numbers to show that 2Fe2+ + Cl2 → 2Fe3+ + 2Cl− is a redox reaction.

  • Iron: +2 → +3, an increase, so Fe2+ is oxidised. ✓
  • Chlorine: 0 → −1, a decrease, so chlorine is reduced. Both happen, so it is redox. ✓
05
Recall
[2 marks]

(Extended) Define oxidising agent and reducing agent.

  • Oxidising agent: a substance that oxidises another substance and is itself reduced (it gains electrons). ✓
  • Reducing agent: a substance that reduces another substance and is itself oxidised (it loses electrons). ✓
06
Recall
[2 marks]

(Extended) Describe a test to show that a solution contains an oxidising agent, giving the result.

  • Add aqueous potassium iodide. ✓
  • It turns from colourless to brown (iodine forms), showing an oxidising agent is present. ✓

Mark this once you have attempted all six and checked your working. It records a Practiced badge on the topic and adds a one-time bonus. Revealing the solutions alone does not count.