Lead(II) oxide can be reduced by heating it with carbon monoxide gas. The equation for this reaction is: PbO + CO → Pb + CO₂. Explain why this reaction is a redox reaction, referring to both oxidation and reduction in your answer.
Written & reviewed by James Millett — Biology (Imperial College London), PGCE Science (University of Cambridge).
Lead(II) oxide can be reduced by heating it with carbon monoxide gas. The equation for this reaction is: PbO + CO → Pb + CO₂.
Model answer (5 marks)
Lead(II) oxide is reduced because it loses oxygen:
1. In PbO the lead is in the +2 oxidation state and is bonded to one oxygen atom.
2. In the product Pb the lead is in the 0 oxidation state, meaning the oxygen atom has been removed.
Carbon monoxide is oxidised because it gains oxygen:
3. In CO the carbon is in the +2 oxidation state and is bonded to one oxygen atom.
4. In the product CO₂ the carbon is in the +4 oxidation state, indicating it has accepted an additional oxygen atom.
Both the loss of oxygen from PbO and the gain of oxygen by CO occur in the same reaction, so the process is a redox reaction.
1. In PbO the lead is in the +2 oxidation state and is bonded to one oxygen atom.
2. In the product Pb the lead is in the 0 oxidation state, meaning the oxygen atom has been removed.
Carbon monoxide is oxidised because it gains oxygen:
3. In CO the carbon is in the +2 oxidation state and is bonded to one oxygen atom.
4. In the product CO₂ the carbon is in the +4 oxidation state, indicating it has accepted an additional oxygen atom.
Both the loss of oxygen from PbO and the gain of oxygen by CO occur in the same reaction, so the process is a redox reaction.
Examiner tips
- Identify the species that lose and gain oxygen; link this to reduction and oxidation.
- Show the change in oxidation state of the key atoms (Pb and C).
- Explain that both processes happen simultaneously to justify the redox classification.
Common mistakes
- Confusing the direction of electron flow; stating that Pb is oxidised instead of reduced.
- Failing to mention the change in oxidation state of carbon from +2 to +4.
- Treating the reaction as a single substitution rather than a redox process.
Mark scheme (5 marks)
- Reduction is identified as the loss of oxygen
- Lead(II) oxide / PbO loses oxygen (so lead(II) oxide is reduced)
- Oxidation is identified as the gain of oxygen
- Carbon monoxide / CO gains oxygen (so carbon monoxide is oxidised)
- Both oxidation and reduction occur simultaneously / in the same reaction, so it is a redox reaction
Key terms in this question
Related
- All Edexcel A-Level Chemistry (9CH0) revision notes →
- How to answer a "Explain" question →
- Decode the mark scheme abbreviations →
More Oxidation and reduction questions
- Iron can be extracted from iron(III) oxide by reaction with carbon monoxide. The…
- Tin(IV) oxide can be reduced by heating it with carbon. The equation for this re…
- Zinc oxide can be reduced by heating it with carbon. The equation for this react…
- When copper(II) oxide reacts with hydrogen gas, copper metal and water are produ…