Questions over Chapter 11 from past exams



Questions over Chapter 11 from past exams

1. Calculate the freezing/melting point of a solution prepared by dissolving 125-g CaCl2 [FM = 111] in 750-g H2O. [Kf = 1.86 deg/molal]

2. A sample of a non-electrolyte with a mass of 5.247 g is dissolved in 25.00 g water. The solution has a freezing point of -3.4 oC. What is the MM of the substance?

3. A 4.5 molar H2SO4 solution has a density of 1.88 g/cm3. Calculate its molality.

4. Suppose that a solution is made by dissolving 25.0 g of sodium sulfate in enough water to make 250.0 mL of solution. What is the molarity of the solution?

5. Suppose that a solution is made by dissolving 25.0 g of sodium sulfate with 250 mL water. [density of water = 1.0 g/mL]

(a) What is the molality of the solution?

(b) Calculate the mole fraction of sodium sulfate

(c) Calculate the mass percent of sodium sulfate

6. Calculate the molality of an aqueous 4.68 M HCl solution. The solution density is 1.198 g/mL.

7. What is the freezing point of an aqueous 1.500 m sodium chloride solution. [Kf = 1.86 oC/molal]

8. Pure benzene has a vapor pressure of 100 mmHg at a certain temperature. What is the vapor pressure of a solution that contains 0.20 mol of a non-electrolyte per mole benzene?

9. A 5.50 g sample of a non-volatile, non-electrolyte sample was dissolved in 25.0 g of benzene, C6H6. Pure benzene has a vapor pressure of 100 mmHg at a certain temperature. If the solution has a vapor pressure that is 85 mmHg, calculate the molar mass of this sample.

10. What is the osmotic pressure of a 0.30 M NaCl solution at 298 K?

Answers:

1. Tf = -8.4 oC

2. MM = 115 g/mol

3. Concentration = 3.12 molal H2SO4

4. Concentration = 0.70 M Na2SO4;

5. (a) Concentration = 0.70 molal Na2SO4; (b) mole fraction = 0.0125; (c) 9.09%

6. Concentration = 4.55 molal HCl solution

7. Tf = -5.58 oC

8. 80 mmHg

9. MM = 97 g/mol

10. 14.7 atm

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