Transition metals can form ions with different oxidation states. Explain why this property makes transition metals and their compounds useful as catalysts, and give one named example of a transition metal or its compound acting as a catalyst in a specific reaction.
Written & reviewed by James Millett — Biology (Imperial College London), PGCE Science (University of Cambridge).
Many industrial and biological processes rely on catalysts to increase the rate of reaction. Transition metals are particularly valued for this role due to their variable oxidation states.
Model answer (5 marks)
Transition metals can exist in several oxidation states, e.g. Fe²⁺/Fe³⁺, Cu⁺/Cu²⁺.
This variability allows a metal ion to accept electrons from a reactant, forming a reduced intermediate, and then donate electrons to another reactant, forming an oxidised intermediate.
Thus the metal cycles through different oxidation states during the reaction, but at the end of the catalytic cycle it returns to its original state, so it is not consumed.
A classic example is the use of platinum (Pt) as a catalyst in the hydrogenation of ethene to ethane.
Pt is regenerated after each cycle, making it an efficient catalyst for this industrial process.
This variability allows a metal ion to accept electrons from a reactant, forming a reduced intermediate, and then donate electrons to another reactant, forming an oxidised intermediate.
Thus the metal cycles through different oxidation states during the reaction, but at the end of the catalytic cycle it returns to its original state, so it is not consumed.
A classic example is the use of platinum (Pt) as a catalyst in the hydrogenation of ethene to ethane.
Pt is regenerated after each cycle, making it an efficient catalyst for this industrial process.
Examiner tips
- Use the word ‘variable oxidation states’ early. Show the electron‑transfer cycle (accept then donate). Mention regeneration explicitly. Give a specific metal and reaction, e.g. Pt – hydrogenation of ethene.
- common_mistakes
- :
- Failing to state that the metal returns to its original state. Giving a non‑catalytic example such as a salt. Using a metal that does not have multiple stable oxidation states.
Mark scheme (5 marks)
- Transition metals have variable oxidation states (can form ions with different charges)
- This allows the transition metal to accept and then donate electrons to/from reacting particles
- The catalyst is regenerated / returns to its original oxidation state at the end of the reaction
- Correct named transition metal or compound acting as a catalyst
- Correct named reaction or process linked to the named catalyst
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 →
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