What is the vapor pressure at 25°C of a solution composed of 42.71 g of naphthalene (a non-volatile compound,?

Question

What is the vapor pressure at 25°C of a solution composed of 42.71 g of naphthalene (a non-volatile compound, MW = 128 g/mol) and 40.65 g of ethanol (MW = 46.02 g/mol). Given the vapor pressure of pure ethanol at 25°C is 96 torr.

hcbiochem · Accepted Answer

The vapor pressure of this kind of solvent is related to the mole fraction of the solvent and its pure vapor pressure:

Vapor Pressure(solution) = mole fraction of solvent X pure vapor pressure

So, 

Moles naphthalene = 42.71 g / 128 g/mol = 0.334 mol naphthalene

moles ethanol = 40.65 g / 46.02 g/mol = 0.883 mol

Mole fraction ethanol = 0.883 / (0.883 + 0.334) = 0.726

Vapor pressure of solution = 96 torr X 0.726 = 70 torr

What is the vapor pressure at 25°C of a solution composed of 42.71 g of naphthalene (a non-volatile compound,?

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