Aqueous solutions of the same solute have molalities of 0.25 mol kg⁻¹ and 0.75 mol kg⁻¹. They are mixed using equal masses of water. What is the molality of the resulting solution?
Answer and explanation
Correct answer: 0.50 mol kg⁻¹
Molality is moles of solute divided by kilograms of solvent. Because equal masses of water are used, take 1.00 kg of water from each solution. The first contributes 0.25 mol solute and the second contributes 0.75 mol, giving 1.00 mol in total. The total solvent mass is 2.00 kg, so the resulting molality is 1.00/2.00 = 0.50 mol kg⁻¹. Equal solvent masses make this the average of the two molalities.
Frequently asked questions
What is the correct answer to this question?
0.50 mol kg⁻¹
Why is this the correct answer?
Molality is moles of solute divided by kilograms of solvent. Because equal masses of water are used, take 1.00 kg of water from each solution. The first contributes 0.25 mol solute and the second contributes 0.75 mol, giving 1.00 mol in total. The total solvent mass is 2.00 kg, so the resulting molality is 1.00/2.00 = 0.50 mol kg⁻¹. Equal solvent masses make this the average of the two molalities.
Which subject and chapter does this question cover?
This is a Class 11 Chemistry question. Chapter: Chapter 01: Solutions.
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