Calculate the vapor pressure (in torr) at 298 K in a solution prepared by dissolving 38.5 g of the non-volatile non-electrolye urea {CO(NH2)2} in 142 g of methanol. The vapor pressure of methanol at 298 K is 122.7 torr. Give your answer to 2 decimal places.

The vapor pressure of methanol solution at 298K is 107.12 torr

Explanation:

As the relative lowering of vapor pressure is directly proportional to the amount of dissolved solute.

The formula for relative lowering of vapor pressure will be,

where,

= relative lowering in vapor pressure

i = Van'T Hoff factor = 1 (for non electrolytes)

= mole fraction of solute  =

Given : 38.5 g of urea is present in 142 g of methanol

moles of solute (urea) =

moles of solvent (methanol) =

Total moles = moles of solute  + moles of solvent  = 0.64 + 4.4 = 5.04

= mole fraction of solute  =

Thus the vapor pressure of methanol solution at 298K is 107.12 torr