Zinc is a metal that can be extracted from zinc oxide by heating it with carbon. Explain why zinc can be extracted using carbon, but magnesium cannot be extracted from magnesium oxide in the same way.
Written & reviewed by James Millett — Biology (Imperial College London), PGCE Science (University of Cambridge).
Zinc oxide can be reduced to zinc by heating with carbon. Magnesium is higher in the reactivity series than both zinc and carbon.
Model answer (4 marks)
1. Carbon is less reactive than zinc.
2. In a reduction reaction, the reducing agent must be more reactive than the metal to be extracted.
3. Therefore carbon can displace zinc from ZnO, producing Zn metal and CO/CO₂.
4. Magnesium is more reactive than carbon, so carbon cannot reduce MgO; a different method such as electrolysis is required.
2. In a reduction reaction, the reducing agent must be more reactive than the metal to be extracted.
3. Therefore carbon can displace zinc from ZnO, producing Zn metal and CO/CO₂.
4. Magnesium is more reactive than carbon, so carbon cannot reduce MgO; a different method such as electrolysis is required.
Examiner tips
- Use the reactivity series to justify the ability of carbon to reduce ZnO but not MgO.
- Show the logical sequence: reactivity comparison → feasibility of reduction → need for alternative method.
- Include the term "reducing agent" and "displace" to match the scheme.
- Mention the specific products (CO/CO₂) only if space allows, but not essential for full marks.
Common mistakes
- Confusing the direction of displacement (writing carbon displaces magnesium).
- Failing to state that carbon is less reactive than zinc but more reactive than magnesium.
- Using vague terms like "reactive" without comparison to the reactivity series.
Mark scheme (4 marks)
- Carbon can only displace/reduce metals that are less reactive than carbon itself
- Zinc is less reactive than carbon, so carbon displaces/reduces zinc from zinc oxide
- Magnesium is more reactive than carbon
- Therefore carbon cannot displace/reduce magnesium from magnesium oxide, so a different method (e.g. electrolysis) is needed
Related
- All Eduqas GCSE Chemistry revision notes →
- How to answer a "Explain" question →
- Decode the mark scheme abbreviations →
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