If 10 g of a solute dissolved in 500 g of solvent produces a molality of 0.2 mol kg⁻¹, what is the molar mass of the solute?
Answer and explanation
Correct answer: 100 g mol⁻¹
Molality is m = moles of solute divided by kilograms of solvent. The solvent mass is 500 g = 0.5 kg. Therefore, moles of solute = 0.2 mol kg⁻¹ × 0.5 kg = 0.1 mol. Molar mass equals the mass of solute divided by its amount: M = 10 g ÷ 0.1 mol = 100 g mol⁻¹. Thus, option B is correct. The key step is converting grams of solvent into kilograms before applying the molality formula.
Frequently asked questions
What is the correct answer to this question?
100 g mol⁻¹
Why is this the correct answer?
Molality is m = moles of solute divided by kilograms of solvent. The solvent mass is 500 g = 0.5 kg. Therefore, moles of solute = 0.2 mol kg⁻¹ × 0.5 kg = 0.1 mol. Molar mass equals the mass of solute divided by its amount: M = 10 g ÷ 0.1 mol = 100 g mol⁻¹. Thus, option B is correct. The key step is converting grams of solvent into kilograms before applying the molality formula.
Which subject and chapter does this question cover?
This is a Class 11 Chemistry question. Chapter: Chapter 01: Solutions.
