An aqueous solution has molality 5. What is the approximate mole fraction of solute?
Answer and explanation
Correct answer: 0.083
A 5 molal aqueous solution contains 5 mol of solute in 1 kg of water. Taking the molar mass of water as 18 g mol−1, 1 kg water contains 1000 ÷ 18 ≈ 55.5 mol water. Total moles are therefore 5 + 55.5 = 60.5 mol. The solute mole fraction is 5 ÷ 60.5 ≈ 0.083. Thus option B is correct; molality itself is not a mole fraction.
Frequently asked questions
What is the correct answer to this question?
0.083
Why is this the correct answer?
A 5 molal aqueous solution contains 5 mol of solute in 1 kg of water. Taking the molar mass of water as 18 g mol−1, 1 kg water contains 1000 ÷ 18 ≈ 55.5 mol water. Total moles are therefore 5 + 55.5 = 60.5 mol. The solute mole fraction is 5 ÷ 60.5 ≈ 0.083. Thus option B is correct; molality itself is not a mole fraction.
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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