Answer to Question #81334 in General Chemistry for Hannah Weber

Question

The vapor pressure of diethyl ether (ether) is 463.57 mm Hg at 25°C.

How many grams of cholesterol, C27H46O, a nonvolatile, nonelectrolyte (MW = 386.6 g/mol), must be added to 214.0 grams of diethyl ether to reduce the vapor pressure to 454.67 mm Hg ?

diethyl ether = CH3CH2OCH2CH3 = 74.12 g/mol.

Answer 1

By Raoult's Law,
vapor pressure = (mole fraction of solvent)(vapor pressure of pure solvent)
454.67 mm Hg = (X)(463.57 mm Hg)
X = 0.9808

(214.0 g H2O)(mol / 74.12 g) = 2.887 mol CH3CH2OCH2CH3

(2.887 mol CH3CH2OCH2CH3)(mol solution / 0.9808 mol H2O) = 2.944 mol solution

2.944 – 2.887 mol = 0.057 mol solute

(0.057 mol)(386 g / mol) = 22 g