A 68 percent by mass nitric acid solution has density 1.42 g mL−1. What is its approximate molarity?
Answer and explanation
Correct answer: 15.3 mol L−1
Molarity is the number of solute moles in one litre of solution. For 1 L solution, density gives mass = 1.42 × 1000 = 1420 g. Since the solution is 68% HNO3 by mass, acid mass = 0.68 × 1420 = 965.6 g. Using molar mass HNO3 = 63 g mol−1, moles = 965.6/63 ≈ 15.3 mol. Therefore the molarity is about 15.3 mol L−1, so option B is correct; the other values use an incorrect percentage or volume.
Frequently asked questions
What is the correct answer to this question?
15.3 mol L−1
Why is this the correct answer?
Molarity is the number of solute moles in one litre of solution. For 1 L solution, density gives mass = 1.42 × 1000 = 1420 g. Since the solution is 68% HNO3 by mass, acid mass = 0.68 × 1420 = 965.6 g. Using molar mass HNO3 = 63 g mol−1, moles = 965.6/63 ≈ 15.3 mol. Therefore the molarity is about 15.3 mol L−1, so option B is correct; the other values use an incorrect percentage or volume.
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.
