The mole fraction of solute is 0.1. If moles of solvent are 9, how many moles of solute are present?
Answer and explanation
Correct answer: 1 mol
Let n denote the unknown moles of solute. Because the solution contains solute and solvent, the total moles are n + 9. The definition of solute mole fraction therefore gives n/(n + 9) = 0.1. Multiplying through, n = 0.1n + 0.9, so 0.9n = 0.9 and n = 1 mol. Therefore, option B is correct. Substitution verifies the answer: 1/(1 + 9) = 1/10 = 0.1. A common error is to divide by the solvent moles alone or to calculate 0.1 × 9 = 0.9 mol; that ignores the fact that solute moles are also part of the denominator. The total-mole definition is essential.
Frequently asked questions
What is the correct answer to this question?
1 mol
Why is this the correct answer?
Let n denote the unknown moles of solute. Because the solution contains solute and solvent, the total moles are n + 9. The definition of solute mole fraction therefore gives n/(n + 9) = 0.1. Multiplying through, n = 0.1n + 0.9, so 0.9n = 0.9 and n = 1 mol. Therefore, option B is correct. Substitution verifies the answer: 1/(1 + 9) = 1/10 = 0.1. A common error is to divide by the solvent moles alone or to calculate 0.1 × 9 = 0.9 mol; that ignores the fact that solute moles are also part of the denominator. The total-mole definition is essential.
Which subject and chapter does this question cover?
This is a Class 11 Chemistry question. Chapter: Chapter 01: Solutions.
