Carbon (coke) is an effective reducing agent for extracting iron and zinc from their oxides, but it cannot be used to extract sodium or aluminium from their oxides. Why not? How are sodium and aluminium extracted instead?
Generated by claude-sonnet-4-6 · 2026-06-26 01:06 · grounding rag
Model Answer
Carbon cannot reduce the oxides of sodium and aluminium because these metals have more affinity for oxygen than carbon. Since they are higher than carbon in the reactivity series, carbon cannot displace them from their oxides.
Extraction of Sodium: Sodium is extracted by electrolytic reduction of molten sodium chloride (NaCl).
- At cathode: Na⁺ + e⁻ → Na
- At anode: 2Cl⁻ → Cl₂ + 2e⁻
Extraction of Aluminium: Aluminium is extracted by electrolytic reduction of molten aluminium oxide (Al₂O₃).
Source: Chapter 3, Section 3.4.5
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Explanation
- The key reason is relative affinity for oxygen: Na and Al bind oxygen more strongly than carbon does, so carbon cannot act as a reducing agent for them.
- The examiner expects you to name electrolysis/electrolytic reduction as the method and mention the molten compound used (NaCl for Na; Al₂O₃ for Al).
- Writing the electrode reactions for sodium earns extra credit and shows depth — include them if marks allow.
- Do not confuse electrolytic refining (purification) with electrolytic reduction (extraction). These are different processes.