Raoult’s Law
1. Glycerin, C3H8O3, is a nonvolatile liquid. What is the vapor pressure of a solution made by adding 164 g of
glycerin to 338 ml of water at 39.8 ◦C. (The vapor pressure of pure water at 39.8 ◦C is 54.74 torr and its density
is 0.992 g/ml.
2. At 29◦C pure water has a vapor pressure of 31.1 torr. A solution is prepared by adding 86.7 g of “Y”, a
nonvolatile, nonelectrolyte to 350.0 g of water. The vapor pressure of the resulting solution is 28.6 torr.
Calculate the molar mass of Y.
3. What is the vapor pressure of a solution made by adding 52.9 g of CuCl2, a strong electrolyte, to 800.0 ml of
water at 52.0◦C? The vapor pressure of water at 52.0◦C is 102.1 torr and its density is 0.987 g/ml.
4. The vapor pressure of pure hexane (C6H14) at 60◦C is 573 torr. That of pure benzene (C6H6) at 60.0◦C is 391
torr. What is the vapor pressure of a solution prepared by mixing 58.9g of hexane with 44.0g of benzene?
5. A solution if prepared by mixing 50.0g of glucose (C6H12O6) with 600.0g water. What is the vapor pressure
of this solution at 25◦C? At 25◦C the vapor pressure of pure water is 23.8 torr.
6. A solution is made by dissolving 25.8 g of urea (CH4N2O), a nonelectrolyte, in 275g of water. Calculate the
vapor pressures of this solution at 25◦C and 45◦C. The vapor pressure of pure water is 23.8 torr at 25◦C and
71.9 torr at 45◦C.
7. Pentane (C5H12) and hexane (C6H14) form an ideal solution. At 25◦C the vapor pressures of pentane and
hexane are 511 and 150. Torr, respectively. A solution is prepared by mixing 25ml pentane (density 0.63 g/ml)
with 45 ml hexane (density 0.66 g/ml).
a. What is the vapor pressure of the resulting solution?
b. What is the composition by mole fraction of pentane in the vapor that is in equilibrium with this solution?
8. Which of the following will have the lowest vapor pressure at 25◦C?
a. pure water
b. a solution of glucose (C6H12O6) in water with Xglucose = 0.01
c. a solution of sodium chloride in water with XNaCl = 0.01
d. a solution of methanol (CH3OH) in water with Xmethanol = 0.2. Consider the vapor pressure of both methanol
(143 torr at 25C and water).
9. What is the vapor pressure of a solution made by dissolving 5.00g of a nonvolatile substance, C6H6O, in
45.0g of benzene? The vapor pressure of benzene, C6H6 at 25◦C is 95 torr.
10. Find the vapor pressure of an aqueous solution containing 60.0g of sugar, C12H22O11, dissolved in 195g of
water. The vapor pressure of pure water at 25C is 23.8 torr.