A solution has solute mole fraction 0.02. If the solvent is water, what is the approximate molality?
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Answer and explanation
Correct answer: 1.13 mol kg−1
Use a basis of 1 total mole of solution. Then solute moles = 0.02 and water moles = 0.98. Water mass is 0.98 × 18 = 17.64 g = 0.01764 kg. Molality, defined as solute moles per kilogram of solvent, is 0.02 ÷ 0.01764 = 1.13 mol kg−1 approximately. Therefore B is correct; total solution mass is not the denominator.
Frequently asked questions
What is the correct answer to this question?
1.13 mol kg−1
Why is this the correct answer?
Use a basis of 1 total mole of solution. Then solute moles = 0.02 and water moles = 0.98. Water mass is 0.98 × 18 = 17.64 g = 0.01764 kg. Molality, defined as solute moles per kilogram of solvent, is 0.02 ÷ 0.01764 = 1.13 mol kg−1 approximately. Therefore B is correct; total solution mass is not the denominator.
Which subject and chapter does this question cover?
This is a Class 11 Chemistry question. Chapter: Chapter 01: Solutions.
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