Problem: Carbon disulfide (CS2 ) boils at 46.30 oC and has a density of 1.261 g/mL.When 5.40 g of a nondissociating unknown is dissolved in 50.0 mL of CS2, the solution boils at 47.08 oC. What is the molecular weight of the unknown?

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Establish the colligative property for boiling point elevation and determine the molar mass of the unknown solution using the molality calculated


Recall that the boiling point of a solution is higher than that of the pure solvent and the change in boiling point (ΔT­b) is given by:


Tb = Tb solution - Tb pure solvent



The change in boiling point is also related to the molality of the solution:

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Problem Details

Carbon disulfide (CS2 ) boils at 46.30 oC and has a density of 1.261 g/mL.

When 5.40 g of a nondissociating unknown is dissolved in 50.0 mL of CS2, the solution boils at 47.08 oC. What is the molecular weight of the unknown?

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