How many moles of solute are needed in 400 g solvent to make a 2.5 molal solution?
Answer and explanation
Correct answer: 1.0 mole
Molality is the number of moles of solute per kilogram of solvent, not per litre of solution. Convert 400 g solvent to 0.400 kg. Required moles = molality × solvent mass = 2.5 mol kg−1 × 0.400 kg = 1.0 mol. Therefore, option A is correct. The value 2.5 would apply to 1 kg solvent, while 0.4 is only the converted solvent mass.
Frequently asked questions
What is the correct answer to this question?
1.0 mole
Why is this the correct answer?
Molality is the number of moles of solute per kilogram of solvent, not per litre of solution. Convert 400 g solvent to 0.400 kg. Required moles = molality × solvent mass = 2.5 mol kg−1 × 0.400 kg = 1.0 mol. Therefore, option A is correct. The value 2.5 would apply to 1 kg solvent, while 0.4 is only the converted solvent mass.
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.
