Question

The vapor pressure of a solution containing 53.6 g glycerin (c3h8o3) in 133.7 g ethanol (c2h5oh) is 113 torr at 40°c. calculate the vapor pressure of pure ethanol at 40°c assuming that glycerin is a nonvolatile, nonelectrolyte solute in ethanol.

Answer 1

Moles glycerin = 53.6 g /92 g/mol =0.582  
Moles ehanol = 133.7 g /46 g/mol =2.91  
total moles = 3.492  
Moles fraction ethanol = 2.91 / 3.492 =0.833  
p = p° X  
113 = p° 0.833  
p° = 135.6 torr