A 3 molal glucose solution has density 1.15 g mL−1. What is its approximate molarity?
Answer and explanation
Correct answer: 2.24 mol L−1
Molality is moles of solute per kilogram of solvent, whereas molarity is moles per litre of solution. Take 1 kg water, so 3 mol glucose are present. Glucose mass = 3 × 180 = 540 g; solution mass = 1540 g. Its volume is 1540/1.15 = 1339 mL = 1.339 L. Therefore molarity = 3/1.339 ≈ 2.24 mol L−1, so option B is correct. Options A, C and D result from using an incorrect solution mass or volume.
Frequently asked questions
What is the correct answer to this question?
2.24 mol L−1
Why is this the correct answer?
Molality is moles of solute per kilogram of solvent, whereas molarity is moles per litre of solution. Take 1 kg water, so 3 mol glucose are present. Glucose mass = 3 × 180 = 540 g; solution mass = 1540 g. Its volume is 1540/1.15 = 1339 mL = 1.339 L. Therefore molarity = 3/1.339 ≈ 2.24 mol L−1, so option B is correct. Options A, C and D result from using an incorrect solution mass or volume.
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.
