A solution has 40 percent solute by mass. The molar mass of solute is 80 and solvent is water. What is the approximate mole fraction of solute?
Answer and explanation
Correct answer: 0.130
Choose a convenient 100 g solution basis: it contains 40 g solute and 60 g water. Solute moles = 40/80 = 0.50 mol, while water moles = 60/18 ≈ 3.33 mol. Total moles are about 3.83 mol, so the solute mole fraction is 0.50/3.83 ≈ 0.130. Option B is correct; 0.400 is the mass fraction, not the mole fraction.
Frequently asked questions
What is the correct answer to this question?
0.130
Why is this the correct answer?
Choose a convenient 100 g solution basis: it contains 40 g solute and 60 g water. Solute moles = 40/80 = 0.50 mol, while water moles = 60/18 ≈ 3.33 mol. Total moles are about 3.83 mol, so the solute mole fraction is 0.50/3.83 ≈ 0.130. Option B is correct; 0.400 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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