In a binary solution, the mole fraction of solvent is 0.75 and moles of solute are 3. How many moles of solvent are present?
Answer and explanation
Correct answer: 9 mol
Let y represent the moles of solvent. Because the solution is binary, its only components are solvent and solute, so the total moles are y + 3. The solvent mole fraction is therefore y/(y + 3). Set this equal to the given value: y/(y + 3) = 0.75. Solving gives y = 0.75y + 2.25, so 0.25y = 2.25 and y = 9 mol. Hence option A is correct. Verification gives 9/(9 + 3) = 9/12 = 0.75. The binary condition matters because no third component is added to the denominator. The other choices produce different solvent fractions and therefore cannot satisfy the stated information.
Frequently asked questions
What is the correct answer to this question?
9 mol
Why is this the correct answer?
Let y represent the moles of solvent. Because the solution is binary, its only components are solvent and solute, so the total moles are y + 3. The solvent mole fraction is therefore y/(y + 3). Set this equal to the given value: y/(y + 3) = 0.75. Solving gives y = 0.75y + 2.25, so 0.25y = 2.25 and y = 9 mol. Hence option A is correct. Verification gives 9/(9 + 3) = 9/12 = 0.75. The binary condition matters because no third component is added to the denominator. The other choices produce different solvent fractions and therefore cannot satisfy the stated information.
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.
