Transition metals as catalystsEdexcel A-Level Chemistry: Flashcards

Exam questions on Transition metals as catalysts

1. In the Contact process, sulfur dioxide gas is oxidised to sulfur trioxide gas by oxygen in the presence of a solid vanadium(V) oxide, V₂O₅, catalyst at about 450 °C: 2SO₂(g) + O₂(g) ⇌ 2SO₃(g).
   Write two equations to show how V₂O₅ acts as a catalyst for the oxidation of SO₂ and is regenerated.2 marks
2. A car's catalytic converter contains platinum and rhodium spread as a thin layer over a ceramic honeycomb. It converts carbon monoxide and nitrogen monoxide in exhaust gases into carbon dioxide and nitrogen.
   Suggest why the platinum and rhodium are used as a thin layer on a ceramic honeycomb rather than as solid blocks of metal.2 marks
3. The reaction between iodide ions and peroxodisulfate ions, S₂O₈²⁻(aq) + 2I⁻(aq) → 2SO₄²⁻(aq) + I₂(aq), is very slow, but it is catalysed by a few drops of iron(II) sulfate solution. Standard electrode potentials: S₂O₈²⁻ + 2e⁻ ⇌ 2SO₄²⁻, E° = +2.01 V; Fe³⁺ + e⁻ ⇌ Fe²⁺, E° = +0.77 V; I₂ + 2e⁻ ⇌ 2I⁻, E° = +0.54 V.
   Explain why the uncatalysed reaction is slow, and why iron(II) ions speed it up. State the type of catalysis involved.3 marks