WAEC Chemistry 2023 Objective — Question 12
Question 12 of 50 from the West African Examinations Council (WAEC) Chemistry 2023 Objective paper, with the correct answer and a full explanation.
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If 100 cm3 of a saturated solution of sodium tetraoxosulphate (VI) at 30°C contains 10.5 g of the salt, what would be its solubility at this temperature? [Na2SO4 = 142]
- A. 0.57 mol dm⁻³
- B. 0.60 mol dm⁻³
- C. 0.74 mol dm⁻³Correct
- D. 2.15 mol dm⁻³
Explanation
Mole = 10.5 g ÷ 142 g/mol = 0.0739 mol. Since 0.0739 mol saturates 100 cm3 at 30°C, 1000 cm3 (1 dm3) at the same temperature contains (0.0739/100)×1000 = 0.739 mol. Solubility ≈ 0.74 mol dm⁻³.
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