The vapor pressure of diethyl ether (ether) is 463.57 mm Hg at 25 °C. A nonvolatile, nonelectrolyte that dissolves in diethyl ether is estrogen.

Question

The vapor pressure of diethyl ether (ether) is 463.57 mm Hg at 25 °C. A nonvolatile, nonelectrolyte that dissolves in diethyl ether is estrogen.

Calculate the vapor pressure of the solution at 25 °C when 6.969 grams of estrogen, C₁₈H₂₄O₂ (272.4 g/mol), are dissolved in 218.2 grams of diethyl ether.

diethyl ether = CH₃CH₂OCH₂CH₃ = 74.12 g/mol.

VP(solution) =  ________ mm Hg

Answer 1

The vapor pressure of the pure ether (463.57 mm Hg) will be reduced by the presence of the nonvolatile solute, estrogen. The amount of this decrease is dependent on the mole fraction of the estrogen and the ether.

mols estrogen = 6.969 g x 1 mol / 272.4 g = 0.02558 mols

mols ether = 218.2 g x 1 mol / 74.12 g = 2.944 mols

Total moles = 0.02558 mols + 2.944 mols = 2.970 mols

Mole fraction of ether = 2.944 / 2.970 = 0.9912

Vapor pressure of solution = 0.9912 x 463.57 mm Hg = 459.5 mm Hg