10 g solute is dissolved in 190 g water. If molar mass of solute is 50 what is the molality?
Answer and explanation
Correct answer: 1.05 mol kg−1
Molality is defined as moles of solute per kilogram of solvent, not per kilogram of the entire solution. Moles of solute = 10 g ÷ 50 g mol−1 = 0.20 mol. The water mass is 190 g = 0.190 kg. Thus, molality = 0.20 ÷ 0.190 = 1.0526, approximately 1.05 mol kg−1. Therefore option B is correct; using 10 g or 200 g as the solvent mass would produce distractor values.
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What is the correct answer to this question?
1.05 mol kg−1
Why is this the correct answer?
Molality is defined as moles of solute per kilogram of solvent, not per kilogram of the entire solution. Moles of solute = 10 g ÷ 50 g mol−1 = 0.20 mol. The water mass is 190 g = 0.190 kg. Thus, molality = 0.20 ÷ 0.190 = 1.0526, approximately 1.05 mol kg−1. Therefore option B is correct; using 10 g or 200 g as the solvent mass would produce distractor values.
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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