Chapter 13 - Solutions

Raoult’s Law:

1. The vapor pressure of pure water at 20.0°C is 17.5mm Hg. What is the vapor pressure of water above a solution of 1.00m Co(NH2)2 (urea) at 20.0°C?

2. The vapor pressure of benzene (C6H6) at 25°C is 95.1mm Hg. What is the vapor pressure of benzene above a solution in which 5.05g C6H5COOH (benzoic acid) is dissolved in 245g C6H6?

3. The vapor pressures of pure benzene (C6H6) and toluene (C7H8) at 25°C are 95.1 and 28.4mm Hg, respectively. A solution is prepared that has equal mole fractions of C6H6 and C7H8. Determine the vapor pressure of C6H6 and C7H8 and the total vapor pressure above this solution. Consider the solution to be ideal. (Hint... The mole fractions for both are equal to 0.500)

4. What is the vapor pressure of water above an 0.20m glucose (C6H12O6) solution at 20°C? The vapor pressure of pure water at 20°C is equal to 17.5mm Hg.

5. What is the vapor pressure of water above 3.49M glycerol (C3H8O3) solution (d= 1.073g/mL) at 20°C? The vapor pressure of pure water at 20°C is equal to 17.5mm Hg.

6. Suppose 651g of ethylene glycol, HOCH2CH2OH, is dissolved in 1.50kg of water. What is the vapor pressure of the water over the solution at 90°C? The vapor pressure of pure water at 90°C is equal to 525.8mm Hg.

7. Assume you dissolve 10.0g of sucrose, C12H22O11, in 225mL (225g) of water and warm the water to 60°C. What is the vapor pressure of the water over this solution? The vapor pressure of pure water at 60°C is equal to 149.4mm Hg.

8. A 35.0g sample of ethylene glycol is dissolved in 500.0g of water. The vapor pressure of water at 32°C is equal to 35.7mm Hg. What is the vapor pressure of the water-ethylene glycol solution at 32°C?

9. 105g of pure iodine is dissolved in 325g of CCl4 at 65°C. Given that the vapor pressure of CCl4 at this temperature is equal to 531mm Hg, what is the vapor pressure of the resulting solution? (Assume that iodine does not contribute to the vapor pressure)

10. If you dissolve 9.00 g of Co(NH2)2 in 10.0mL of water, what is the resulting vapor pressure at 24°C. Assume the density of water is 1.00/mL and the vapor pressure of pure water is 22.4mm Hg.

Osmotic Prssure:

1. Calculate the osmotic pressure of a sugar solution that contained 100 grams of sucrose, C12H22O11, dissolved in enough water to make 1L of solution at 25°C.

2. Calculate the Osmotic pressure at 50°C of a glucose solution (C6H12O6) that has 60 grams of glucose dissolved in enough water to make 1500 mL.

3. The average osmotic pressure of blood is 7.7atm at 25°C. What concentration of glucose will be isotonic with blood?

4. Which would have a higher osmotic pressure, a 0.10M solution of NaCl or a 0.10M solution of KBr?

5. The osmotic pressure of an aqueous solution of a certain protein was measured in order to determine the protein’s molar mass. The solution contained 3.50mg of protein dissolved in sufficient water to form 5.00mL of solution. The osmotic pressure of the solution at 25°C was found to be 1.54 torr. Calculate the molar mass of the protein.

6. A sample of 2.05g of polystyrene of uniform polymer chain length was dissolved in enough toluene to form 0.100L of solution. The osmotic pressure of this solution was found to be 1.21kPa at 25°C. Calculate the molar mass of the polystyrene.

Colligative Properties:

1. Calculate the freezing point of a 0.75m solution of KCl. Assume 100% dissociation.

2. Calculate the boiling point of a 1.5m solution of AlCl3. Assume 40% dissociation.

3. Calculate the molality of a solution of MgCl2 that has a boiling point of 101.22°C. Assume 78% dissociation.

4. Calculate the freezing point of a 0.0568m solution of H2SO4. Assume 100% dissociation.

5. Calculate the molecular weight of a solution that forms 2 ions, if 13g of the solute are dissolved in 1500g of water. The freezing point of this solution is -1.86°C. Assume 100% dissociation.

6. Calculate the boiling point of a 0.635m solution of H3PO4. Assume 100% dissociation.

7. Calculate the weight of solute in a solution if the number of ions it makes is 5, the molecular weight is 149.5, and the mass of water in the solution is 450g. The percentage of dissociation is 100% and the freezing point of the solution is -5.67°C.

8. Calculate the boiling point of the solution in #7.

9. Calculate the freezing point of a solution containing 32g of CaCl2 in 500g of water. The percentage of dissociation is 75%.

10. Calculate the molality of a solution that has a boiling point of 104.7°C. The solute forms 3 ions in solution and there is 100% dissociation.

11. 35.0g of an organic compound dissolved in 350g of water have a boiling point of 101.5°C. What is the molar mass of the solute?

12. 5.85g of an organic compound dissolved in 75.0g of water has a freezing point of -1.04°C. What is the molar mass of this compound?

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