A solution has 25 mass percent solute. Molar mass of solute is 50 g mol−1 and that of solvent is 18 g mol−1. What is the approximate mole fraction of solute?
Answer and explanation
Correct answer: 0.107
Take 100 g of solution, so it contains 25 g solute and 75 g solvent. The corresponding amounts are 25/50 = 0.50 mol and 75/18 = 4.1667 mol. Total amount is 4.6667 mol. Thus the solute mole fraction is 0.50/4.6667 = 0.107 approximately. Option B is correct; mass percentage itself cannot be used directly as mole fraction because the molar masses differ.
Frequently asked questions
What is the correct answer to this question?
0.107
Why is this the correct answer?
Take 100 g of solution, so it contains 25 g solute and 75 g solvent. The corresponding amounts are 25/50 = 0.50 mol and 75/18 = 4.1667 mol. Total amount is 4.6667 mol. Thus the solute mole fraction is 0.50/4.6667 = 0.107 approximately. Option B is correct; mass percentage itself cannot be used directly as mole fraction because the molar masses differ.
Which subject and chapter does this question cover?
This is a Class 11 Chemistry question. Chapter: Some Basic Concepts of Chemistry. Topic: Percentage composition and empirical/molecular formulas.
