A Levels Chemistry (9701)•9701/11/M/J/22

Explanation
Stoichiometry of CO-NO reaction in catalytic converter
Steps:
- Balanced equation: 2CO + 2NO → 2CO₂ + N₂ (excess NO ensures complete CO reaction).
- Moles of CO = 5 g / 28 g/mol = 0.1786 mol.
- Moles CO₂ = 0.1786 mol; mass CO₂ = 0.1786 × 44 g/mol ≈ 7.86 g ≈ 8 g.
- Moles N₂ = 0.1786 / 2 = 0.0893 mol; mass N₂ = 0.0893 × 28 g/mol ≈ 2.5 g ≈ 2 g.
Why D is correct:
- Matches stoichiometric masses from balanced equation, using standard molar masses (CO=28, CO₂=44, N₂=28) and approximation for given option.
Why the others are wrong:
- A: Produces NO (reactant, not product) with masses from incorrect equation.
- B: CO₂ mass correct, but 9.2 g N₂ implies ~10.4 g CO (violates given 5 g).
- C: 2.4 g CO₂ implies ~1.5 g CO (wrong stoichiometry); 9.2 g N₂ too high.
Final answer: D
Topic: Atoms, molecules and stoichiometry
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