A student is assigned a molecular weight determination by means of a colligative
ID: 909780 • Letter: A
Question
A student is assigned a molecular weight determination by means of a colligative property measurement. He dissolves his entire sample of unknown (20.40 g) in 846.0 g of a mysterious solvent called duffanol and measures a boiling point of 162.0 °C and a freezing point of -54.2°C. He then tries to find data on duffanol but can only locate the following for pure duffanol:
Boiling point of 155.0 °C
H of sublimation is 42106.0 J/mol (note that H of sublimation is equal to the sum of HVAP and HFUSION)
Melting point of -53.0 °C
Molecular weight equal to 145.0 g/mol
Clueless as to what to do to calculate a molecular weight, the student contacts another student for help. Assuming the unknown to be non-volatile, and the solution to be dilute and ideal, the second student shows that the molecular weight of the unknown as well as the HVAP and HFUSION for duffanol can be calculated. Please give these values providing details of your calculations.
Explanation / Answer
A student is assigned a molecular weight determination by means of a colligative
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