What is the vapor pressure

Question

Glycerin, C₃H₈O₃, is a nonvolatile liquid. What is the vapor pressure of a solution made by adding 164

g glycerin to 338 mL H2O at 39.8 C? The vapor pressure of pure water at 39.8 C is 54.74 torr, and its 

density is 0.992 g/mL

Answer 1

Molar mass glycerin = 92.1 g / mole

To find the vapor pressure of the solution, we will need to find the mole fraction of glycerin and H2O.

mols glycerin = 164 g glycerin x 1 mol / 92.1 g = 1.781 mols glycerin

mols H2O = 338 mls H2O x 0.992 g / ml x 1 mol / 18.02 g = 18.61 mols H2O

Total mols = 1.781 + 18.61 = 20.39 mols

mol fraction H2O = 18.61 mol / 20.39 mol = 0.9127

Vapor pressure of solution = 0.9127 x 54.74 torr = 49.96 torr = 50.0 torr (3 sig. figs.)