Colligative Properties
*For all problems below, ignore van’t Hoff factors unless indicated otherwise.
1. A solution is created by adding 392.7 g of MgCl2 (Molar mass = 95.211 g/mol) to 2750 mL of water (Kb = 0.510 °C/m,
Kf = 1.86 °C/m, BP = 100.0 °C, MP = 0.0 °C, density = 1.00 g/mL). What is the boiling point and freezing point of the
solution?
2. How many grams of KCl need to be added to 1.50 L of water to lower the freezing point to -3.50 °C?
3. A solution contains 32.0 g of an unknown solid and 300.0 g of ethanol (Kb = 1.22 °C/m, BP = 78.4 °C). What is the
molar mass of unknown solid if the boiling point of the solution is 80.63 °C?
4. Find the vapor pressure of a solution containing 27.4 g of naphthalene (C10H8, molar mass = 128.2 g/mol) dissolved
in 465 g of hexane (C6H14, molar mass = 86.2 g/mol) at 25 °C. The vapor pressure of pure hexane at 25 °C is 151 torr.
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5. Find the vapor pressure of a solution that is 41.3% hexane (% by mole) and 58.7% CCl4 (% by mole) at 25 °C. The
vapor pressures at 25 °C of hexane and CCl4 are 151 torr and 107 torr respectively.
6. A solution made up of dichloromethane (CH2Cl2) and chloroform (CHCl3) has a vapor pressure of 375 torr. Calculate
the mole fraction of the solution and find the percent composition of the vapor. The vapor pressures at 25 °C of
dichloromethane and chloroform are 430. torr and 194 torr respectively.
7. When 29.0 mg of the protein are added to 30.0 mL of water, you find that the osmotic pressure is 4.20 mm Hg.
What is the molar mass of the protein?
8. Repeat Problem #1 using ideal van’t Hoff factors and compare the answers.
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