O Levels Chemistry (5070)•5070/12/O/N/20
Explanation
Percentage Yield from Stoichiometric Ratio
Steps:
- Balanced reaction: Fe₂O₃ → 2Fe (molar masses: Fe₂O₃ = 160 tonnes equiv., 2Fe = 112 tonnes equiv.).
- Theoretical yield of Fe: (112/160) × 80 = 56 tonnes.
- Actual yield: 50 tonnes.
- Percentage yield: (50/56) × 100% ≈ 89%.
Why D is correct:
- Percentage yield formula (actual/theoretical × 100%) yields 89% based on stoichiometric mass ratio.
Why the others are wrong:
- A: 45% ignores stoichiometry, underestimates theoretical yield.
- B: 63% approximates 50/80 × 100%, treating oxide mass as theoretical iron.
- C: 68% miscalculates ratio, possibly inverting masses.
Final answer: D
Topic: Relative masses of atoms and molecules
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