Lead is a metal that has been used by humans for thousands of years. It is sometimes found as a native metal in the Earth's crust, but it is more commonly found as lead sulfide ore (galena). Lead can be extracted from its ore by heating it in air to form lead oxide, which is then heated with carbon. Explain why lead can be extracted using carbon, and why this method cannot be used to extract sodium from sodium oxide.

Eduqas GCSE Chemistry — 2.3 Metals and their extraction · Explain · 4 marks · View as Markdown

Written & reviewed by James Millett — Biology (Imperial College London), PGCE Science (University of Cambridge).

Lead has been smelted since ancient times. Sodium, by contrast, was not isolated until 1807, when electricity became available as a tool for chemists.

Model answer (4 marks)

Carbon is more reactive than lead, so it can displace oxygen from lead oxide:
1. Carbon reacts with the oxygen in PbO to form CO or CO₂, leaving Pb metal.
2. The reaction removes the oxygen, reducing PbO to Pb.
Sodium, however, is more reactive than carbon. Carbon cannot displace oxygen from Na₂O because Na would be oxidised back to Na⁺ if it tried to react with carbon. Thus carbon cannot reduce sodium oxide; electrolysis is required to obtain sodium metal.

Examiner tips

  • Use the term ‘displace’ or ‘reduce’ to show understanding of redox; mention carbon’s higher reactivity; explain why the same method fails for sodium by citing its higher reactivity than carbon.
  • Show the two-step process for lead (oxidation of carbon, reduction of PbO) and contrast with sodium’s need for electrolysis.

Common mistakes

  • Confusing the role of carbon as a reducing agent with it being oxidised; writing that carbon is oxidised to CO₂ rather than CO.
  • Saying that sodium can be reduced by carbon because it is a metal, ignoring its higher reactivity; or claiming the same method works for sodium without mentioning electrolysis.

Mark scheme (4 marks)

  1. Carbon can displace / remove oxygen from lead oxide because carbon is more reactive than lead
  2. Carbon reduces the lead oxide / removes oxygen from the lead oxide, leaving lead metal
  3. Sodium cannot be extracted using carbon because sodium is more reactive than carbon
  4. Therefore carbon cannot displace / reduce sodium from sodium oxide / electrolysis is needed instead

Key terms in this question

ore · native metal

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