Problem: The vapor above a mixture of pentane and hexane at room temperature contains 35.5% pentane by mass. What is the mass percent composition of the solution? Pure pentane and hexane have vapor pressures of 425 torr and 151 torr, respectively, at room temperature.

FREE Expert Solution

Take 100 g basis for the mass of vapor: 

mass pentane = 35.5g 

mass hexane = 64.5g 



Convert these values to mol using their molecular weights:

Pentane

M = 72.15 g/mol 

 35.5 g × 1 mol72.15 g= 0.492 mol


Hexane: 

M = 86.18 g/mol 

64.5 g × 1 mol86.18 g= 0.748 mol


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Problem Details

The vapor above a mixture of pentane and hexane at room temperature contains 35.5% pentane by mass. What is the mass percent composition of the solution? Pure pentane and hexane have vapor pressures of 425 torr and 151 torr, respectively, at room temperature.


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