In an aqueous solution the mole fraction of solute is 0.01. What is the approximate molality?
Answer and explanation
Correct answer: 0.56 mol kg−1
Take 1 mol of total solution: solute moles are 0.01 and water moles are 0.99. The solvent mass is 0.99 × 18 = 17.82 g = 0.01782 kg. Molality is moles of solute per kilogram of solvent, so m = 0.01/0.01782 ≈ 0.561 mol kg⁻¹, which rounds to 0.56 mol kg⁻¹. Therefore option B is correct.
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What is the correct answer to this question?
0.56 mol kg−1
Why is this the correct answer?
Take 1 mol of total solution: solute moles are 0.01 and water moles are 0.99. The solvent mass is 0.99 × 18 = 17.82 g = 0.01782 kg. Molality is moles of solute per kilogram of solvent, so m = 0.01/0.01782 ≈ 0.561 mol kg⁻¹, which rounds to 0.56 mol kg⁻¹. Therefore option B is correct.
Which subject and chapter does this question cover?
This is a Class 11 Chemistry question. Chapter: Some Basic Concepts of Chemistry. Topic: Mole concept and molar mass.
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