A solution has mole fraction of solute 0.2 and the solvent is water. What is the approximate molality of the solution?
Answer and explanation
Correct answer: 13.9 mol kg−1
For a binary solution, take 1 mol of total solution. The solute amount is 0.2 mol and water is 0.8 mol. The solvent mass is 0.8 × 18 = 14.4 g = 0.0144 kg. Molality equals moles of solute divided by kilograms of solvent, so m = 0.2/0.0144 = 13.89 mol kg−1, approximately 13.9 mol kg−1. Hence B is correct; using total solution mass or 1 kg water without conversion produces the distractors.
Frequently asked questions
What is the correct answer to this question?
13.9 mol kg−1
Why is this the correct answer?
For a binary solution, take 1 mol of total solution. The solute amount is 0.2 mol and water is 0.8 mol. The solvent mass is 0.8 × 18 = 14.4 g = 0.0144 kg. Molality equals moles of solute divided by kilograms of solvent, so m = 0.2/0.0144 = 13.89 mol kg−1, approximately 13.9 mol kg−1. Hence B is correct; using total solution mass or 1 kg water without conversion produces the distractors.
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.
