Sample Problems – Chapter 14
Some useful constants:
solvent
Acetic acid
Benzene
Chloroform
Naphthalene
Water
normal boiling
point, °C
Kb, °C/m
freezing point,
°C
Kf, °C/m
118.9
80.1
61.2
–
100.0
3.1
2.53
3.63
–
0.512
16.6
5.5
–
80.22
0.00
3.9
5.12
–
6.85
1.86
1. What is the mole fraction of H2 in a gaseous mixture containing 1.0 g H2, 8.0 g O2, and 16 g
CH4?
2. Determine the mole fractions of both substances in a solution containing 36.0 g water and
46.0 g glycerin, C3H5(OH)3.
3. A solution contains 10.0 g acetic acid, CH3COOH, in 125 g water. What is the concentration
of the solution expressed as (a) mole fractions of CH3COOH and H2O; (b) molality of
CH3COOH?
4. Calculate the molalities and the mole fractions of acetic acid in two solutions prepared by
dissolving 120 g acetic acid (a) in 100 g water; (b) in 100 g ethyl alcohol, C2H5OH.
5. Calculate the molality of a solution containing:
(a) 0.65 mol glucose, C6H12O6, in 250 g water;
(b) 45 g glucose in 1.00 kg water;
(c) 18 g glucose in 200 g water.
6. How many g CaCl2 should be added to 300 mL water to make up a 2.46 m solution?
7. Calculate the molarity, molality, and mole fraction of ethyl alcohol, C2H5OH, in a solution of
total volume 95 mL prepared by adding 50 mL ethyl alcohol (density = 0.789 g/mL) to 50
mL water (density = 1.0 g/mL).
8. The density of 10.0% by mass KCl solution in water is 1.06 g/mL. Calculate the molarity,
molality, and mole fraction of KCl in this solution.
9. The vapor pressure of pure liquid solvent A is 0.80 atm. When a nonvolatile substance B is
added to the solvent, its vapor pressure drops to 0.60 atm. What is the mole fraction of
component B in the solution?
10. The vapor pressure of pure water at 26°C is 25.21 torr. What is the vapor pressure of a
solution which contains 20.0 g glucose, C6H12O6, in 70 g water at the same temperature?
11. The vapor pressure of pure water at 25°C is 23.76 torr. The vapor pressure of a solution
containing 5.40 g of a nonvolatile substance in 90.0 g water is 23.32 torr. Compute the
molecular weight of the solute.
12. At 30°C, pure benzene, C6H6, has a vapor pressure of 121.8 torr. Dissolving 15.0 g of a
nonvolatile solute in 250 g of benzene produced a solution having a vapor pressure of 120.2
torr. Determine the approximate molecular weight of the solute.
13. The vapor pressure of water at 28°C is 28.35 torr. Compute the vapor pressure lowering at
28°C of a solution containing 68 g of cane sugar, C12H22O11, in 1000 g of water.
14. What is the freezing point of a 10% (by weight) solution of CH3OH in water?
15. When 10.6 g of a nonvolatile substance is dissolved in 740 g of ether, its boiling point is
raised by 0.284°C. What is the molecular weight of the substance? For ether Kb = 2.11 °C/m.
16. The freezing point of a sample of naphthalene was found to be 80.6°C. When 0.512 g of a
substance is dissolved in 7.03 g naphthalene, the solution has a freezing point of 75.2°C.
What is the molecular weight of the solute?
17. How much ethyl alcohol, C2H5OH, must be added to 1.00 L of water so that the solution will
not freeze at –20°C?
18. If the radiator of an automobile contains 12 L of water, how much would be the freezing
point lowered by the addition of 5 kg of Prestone (glycol, C2H4(OH)2)?
19. An aqueous solution containing 288 g of a nonvolatile compound in 90.0 g of water boils at
101.24°C at 1.00 atm pressure. What is the molecular weight of the compound?
20. A solution containing 3.24 g of a nonvolatile compound and 200 g of water boils at
100.130°C at 1 atm. What is the molecular weight of the solute?