0.2 mole urea is dissolved in 200 g water. What is the molality?
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Answer and explanation
Correct answer: 1.0 mol kg⁻¹
Molality uses the mass of solvent, not the final solution volume. Convert 200 g water to 0.200 kg, then use m = moles of solute/mass of solvent = 0.200/0.200 = 1.0 mol kg⁻¹. The common error is to leave the solvent mass in grams or use solution mass.
Frequently asked questions
What is the correct answer to this question?
1.0 mol kg⁻¹
Why is this the correct answer?
Molality uses the mass of solvent, not the final solution volume. Convert 200 g water to 0.200 kg, then use m = moles of solute/mass of solvent = 0.200/0.200 = 1.0 mol kg⁻¹. The common error is to leave the solvent mass in grams or use solution mass.
Which subject and chapter does this question cover?
This is a Class 11 Chemistry question. Chapter: Chapter 01: Solutions.
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