If 0.1 mole sodium chloride is dissolved in 900 g water, what is the molality?
Answer and explanation
Correct answer: About 0.111 mole per kilogram
Molality uses the mass of solvent in kilograms: m = moles of solute/kg of solvent. Convert 900 g water to 0.900 kg, then calculate m = 0.1/0.900 = 0.111... mol kg⁻¹. Therefore option A is correct. The value 0.900 is the solvent mass in kilograms, not the answer, and using solution volume would incorrectly change the concentration measure to molarity.
Frequently asked questions
What is the correct answer to this question?
About 0.111 mole per kilogram
Why is this the correct answer?
Molality uses the mass of solvent in kilograms: m = moles of solute/kg of solvent. Convert 900 g water to 0.900 kg, then calculate m = 0.1/0.900 = 0.111... mol kg⁻¹. Therefore option A is correct. The value 0.900 is the solvent mass in kilograms, not the answer, and using solution volume would incorrectly change the concentration measure to molarity.
Which subject and chapter does this question cover?
This is a Class 11 Chemistry question. Chapter: Chapter 01: Solutions.
