A solution has molarity 2.5 M and density 1.25 g mL−1. The molar mass of solute is 100 g mol−1. What is the mass percent of the solution?
Answer and explanation
Correct answer: 20 percent
Use a 1 L sample because molarity directly gives the solute moles in that volume. Solute moles = 2.5 mol, so solute mass = 2.5 × 100 = 250 g. Density gives solution mass = 1.25 × 1000 = 1250 g. Therefore mass percent = (250/1250) × 100 = 20%, making option C correct. Molarity alone would not provide solution mass; the density is needed for the denominator.
Frequently asked questions
What is the correct answer to this question?
20 percent
Why is this the correct answer?
Use a 1 L sample because molarity directly gives the solute moles in that volume. Solute moles = 2.5 mol, so solute mass = 2.5 × 100 = 250 g. Density gives solution mass = 1.25 × 1000 = 1250 g. Therefore mass percent = (250/1250) × 100 = 20%, making option C correct. Molarity alone would not provide solution mass; the density is needed for the denominator.
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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