# Exercise 6 | Colligative Properties of Solutions

The vapor pressure of pure water at 65oC is 412 torr.

What is the vapor pressure at 65oC of a solution prepared from 100 mL of water (density 1.00 g/mL) and 120 g of diglyme, C6H14O3, a nonvolatile substance?

Raoult’s Law:

Pwater = xwater P0water

Pwater = vapor pressure of the water in the solution

xwater = mole fraction of water in the solution

P0water = vapor pressure of the pure water

xwater =

nwater = $\frac{{\mathrm{m}}_{\mathrm{water}}}{{\mathrm{M}}_{\mathrm{water}}}$ = $\frac{100}{18.0}$  = 5.55 mol

ndiglyme = $\frac{{\mathrm{m}}_{\mathrm{diglyme}}}{{\mathrm{M}}_{\mathrm{diglyme}}}$ = $\frac{120}{134.17}$ = 0.894 mol

xwater = $\frac{5.55}{6.45}$ = 0.861

Pwater = xwater P0water = 0.861 x 412 = 355 torr