If a 0.5 m solution is prepared using 0.2 kg of solvent, how many moles of solute are present?
Answer and explanation
Correct answer: 0.10 mol
Molality is the amount of solute in moles divided by the mass of solvent in kilograms: m = n/mass of solvent. Rearranging gives n = m × mass of solvent. Substitution gives n = 0.5 mol kg⁻¹ × 0.2 kg = 0.10 mol. The solvent mass, rather than the total solution mass, must be used. Thus, option B is correct. The result also has the proper unit, mol.
Frequently asked questions
What is the correct answer to this question?
0.10 mol
Why is this the correct answer?
Molality is the amount of solute in moles divided by the mass of solvent in kilograms: m = n/mass of solvent. Rearranging gives n = m × mass of solvent. Substitution gives n = 0.5 mol kg⁻¹ × 0.2 kg = 0.10 mol. The solvent mass, rather than the total solution mass, must be used. Thus, option B is correct. The result also has the proper unit, mol.
Which subject and chapter does this question cover?
This is a Class 12 Chemistry question. Chapter: Chapter 01: Solutions. Topic: 2: Concentration Metrics.
