A solution containing ethylene glycol and water has a vapor pressure of 7.88 torr at 10∘c. Pure water has a vapor pressure of 9.21 torr at 10∘c. What is the mole fraction of ethylene glycol in the solution?

0.144.

Explanation:

Change in vapor pressure = ΔPsolvent = P of the pure solvent (water) - P of the mixture = 9.21 torr - 7.88 torr = 1.33 torr.

∵ ∆Psolvent = (Xsolute, ethylene glycol) (Pºsolvent, water)

where, Xsolute is the mole fraction of the solute (ethylene glycol).

Pºsolvent is the vapor pressure of the pure solvent = 9.21 torr.

∴ Xsolute = ∆Psolvent / Pºsolvent = (1.33 torr) / (9.21 torr) = 0.144.