Q1. [1] medium thorough-understanding
[mcq] In the thermit reaction, iron(III) oxide is reduced to produce molten iron. Which of the following correctly identifies the reducing agent used and the reason carbon cannot be used instead?
((A)) Carbon; it has a higher affinity for oxygen than aluminium at high temperatures
((B)) Aluminium; it is more reactive than iron and has a higher affinity for oxygen than carbon at the reaction temperature
((C)) Aluminium; it is less reactive than iron, so it does not interfere with the product
((D)) Carbon; it is cheaper and more readily available than aluminium
- A Aluminium is cheaper and more readily available than carbon.
- B Aluminium is more reactive than iron and has a greater affinity for oxygen than carbon does at the temperatures involved.
- C Carbon would produce a poisonous gas, making it unsafe to use.
- D Aluminium has a lower melting point than carbon, making it easier to ignite.
Generated by claude-sonnet-4-6 · 2026-06-26 01:06 · grounding rag
Model Answer
Answer: B — Aluminium is more reactive than iron and has a greater affinity for oxygen than carbon does at the temperatures involved.
Explanation
The thermit reaction is: Fe₂O₃ + 2Al → Al₂O₃ + 2Fe. Aluminium is the reducing agent because it is more reactive than iron and displaces it. At the high temperatures of this reaction, aluminium has a greater affinity for oxygen than carbon, so carbon cannot reduce Fe₂O₃ effectively here. The textbook (Chapter 1, Exercise Q2) classifies this as a displacement reaction. Examiners expect you to correctly name aluminium as the reducing agent and justify it by reactivity/oxygen affinity — not by cost or melting point.