O Levels Chemistry (5070)•5070/11/O/N/22

Explanation
Percentage yield from limiting reactant
Steps:
- Moles of Na₂SO₄ = (25/1000) dm³ × 1.0 mol dm⁻³ = 0.025 mol.
- Theoretical moles of BaSO₄ = 0.025 mol (1:1 stoichiometry with excess BaCl₂).
- Theoretical mass of BaSO₄ = 0.025 mol × 233 g mol⁻¹ = 5.825 g.
- Percentage yield = (5.36 g / 5.825 g) × 100% = 92%.
Why C is correct:
- Percentage yield formula (actual mass / theoretical mass) × 100% yields exactly 92% based on molar mass of BaSO₄ (233 g mol⁻¹).
Why the others are wrong:
- A: Error in volume conversion, treating 25 cm³ as 25 dm³.
- B: Divides actual mass by molar mass without moles calculation.
- D: Forgets to convert cm³ to dm³, yielding ~9% from incorrect moles.
Final answer: C
Topic: The mole and the Avogadro constant
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