If the mole fraction of solute is 0.2 and the moles of solvent are 8, how many moles of solute are present?
Answer and explanation
Correct answer: 2 mol
Let n be the moles of solute. The solute mole fraction is the solute amount divided by the total amount, so x = n/(n + 8). Using x = 0.2 gives n/(n + 8) = 0.2. Multiplication and simplification yield n = 0.2n + 1.6, then 0.8n = 1.6, and finally n = 2 mol. Therefore, option A is correct. The value 1.6 mol is only the intermediate product of 0.2 × 8; it cannot be used directly because the unknown solute is included in the total-mole denominator. Substitution confirms the result: 2/(2 + 8) = 2/10 = 0.2.
Frequently asked questions
What is the correct answer to this question?
2 mol
Why is this the correct answer?
Let n be the moles of solute. The solute mole fraction is the solute amount divided by the total amount, so x = n/(n + 8). Using x = 0.2 gives n/(n + 8) = 0.2. Multiplication and simplification yield n = 0.2n + 1.6, then 0.8n = 1.6, and finally n = 2 mol. Therefore, option A is correct. The value 1.6 mol is only the intermediate product of 0.2 × 8; it cannot be used directly because the unknown solute is included in the total-mole denominator. Substitution confirms the result: 2/(2 + 8) = 2/10 = 0.2.
Which subject and chapter does this question cover?
This is a Class 11 Chemistry question. Chapter: Chapter 01: Solutions.
