The mole fraction of water in a solution is 0.9. If moles of water are 9, how many moles of solute are present?
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Answer and explanation
Correct answer: 1.0 mol
Mole fraction of water is the ratio of water moles to total moles. Let the solute amount be x mol. Then 9/(9 + x) = 0.9. Solving gives 9 = 8.1 + 0.9x, so 0.9 = 0.9x and x = 1.0 mol. Equivalently, 9 mol is 90% of the total, so total moles are 10 and solute moles are 1. Option B is correct.
Frequently asked questions
What is the correct answer to this question?
1.0 mol
Why is this the correct answer?
Mole fraction of water is the ratio of water moles to total moles. Let the solute amount be x mol. Then 9/(9 + x) = 0.9. Solving gives 9 = 8.1 + 0.9x, so 0.9 = 0.9x and x = 1.0 mol. Equivalently, 9 mol is 90% of the total, so total moles are 10 and solute moles are 1. Option B is correct.
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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