Molecular weight

Question

10grams of solid parafin wax is dissolved in 50grams of diethylether at 298k.The vapour pressure of the solution is 495mmhg. If the vapour pressure of pure diethylether at 2298k is 510mmhg.find the molecular weight of the parafin wax

Answer 1

First, we'll need to find the mole fraction of the paraffin and then convert that to moles. Once we have the moles, and we know the grams (10 g), we can solve for molar mass = g / moles.

mol fraction diethylether = 495 mm Hg / 510 mm Hg = 0.971

mol fraction paraffin = 1.000 - 0.971 = 0.0294

molar mass diethylether (CH₃CH₂)₂O = 74.1 g / mol

mols diethylether = 50 g x 1 mol / 74.1 g = 0.675 mols

mols paraffin: 0.971 / 0.0294 = 0.675 mol / x mol and x = 0.0204 mols paraffin

Molar mass paraffin = g / mols = 10 g / 0.0204 mols ≈ 490 g / mol