Determination of Molar Mass from Colligative Properties

Determination of Molar Mass from Colligative Properties 

The colligative properties of solutions provide a useful means of determining the molar mass of solutes. Any of the four colligative properties can be used, as shown in Sample Exercises 13.10 and 13.11. 

EXERCISE 13.10 Molar Mass from Freezing-Point Depression 

A solution of an unknown nonvolatile nonelectrolyte was prepared by dissolving 0.250 g of the substance in 40.0 g of CCI4. The boiling point of the resultant solution was 0.357 °C higher than that of the pure solvent. Calculate the molar mass of the solute. 

Analyze Our goal is to calculate the molar mass of a solute based on knowledge of the boiling-point elevation of its solution in CCI4, ATj = 0.357 °C, and the masses of solute and solvent. Table 13.3 gives fCj for the solvent (CCI4), fCj = 5.02 °C/m. 

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Determination of Molar Masses from Colligative Properties... 

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