Determine the vapor pressure of a solution at 25°C that contains 85.3 g of naphthalene (C10H8) in 540 g of benzene (C6H6). The vapor pressure of benzene at 25°C is 74.6 torr.

Answer 1

Raoult's Law:

The vapor pressure of the mixture will be equal to the vapor pressure of pure benzene x the mole fraction of benzene in the mixture. So, find the mole fraction of benzene in the mixture and multiply it by 74.6 torr.

moles naphthalene = 85.3 g x 1 mol/128.2 g = 0.665 moles

moles benzene = 540 g x 1 mol/78.1 g = 6.91 moles

Total moles = 7.58

Mole Fraction of Benzene = 6.91 mol/7.58 mol = 0.912

Vapor Pressure of solution = 0,912 x 74.6 torr = 68.0 torr