A 30 percent by mass urea solution is given. What is the approximate mole fraction of urea?
Answer and explanation
Correct answer: 0.114
Choose a convenient 100 g sample of solution. It contains 30 g urea and 70 g water. Using molar masses urea = 60 g mol−1 and water = 18 g mol−1, the amounts are 30 ÷ 60 = 0.50 mol urea and 70 ÷ 18 ≈ 3.89 mol water. Hence the urea mole fraction is 0.50 ÷ (0.50 + 3.89) ≈ 0.114. Option B is correct; 0.300 is the mass fraction, not the mole fraction.
Frequently asked questions
What is the correct answer to this question?
0.114
Why is this the correct answer?
Choose a convenient 100 g sample of solution. It contains 30 g urea and 70 g water. Using molar masses urea = 60 g mol−1 and water = 18 g mol−1, the amounts are 30 ÷ 60 = 0.50 mol urea and 70 ÷ 18 ≈ 3.89 mol water. Hence the urea mole fraction is 0.50 ÷ (0.50 + 3.89) ≈ 0.114. Option B is correct; 0.300 is the mass fraction, not the mole fraction.
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.
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