NAME: AP CHEMISTRY CHAPTER 8 PROBLEM SET #2 (Questions 1-3) Select the letter of the answer that best completes the statement or answers the question. 1. 2. 3. According to Raoult s Law, which statement is false? A. The vapor pressure of a solvent over a solution is less than that of the pure solvent. B. Ionic solids ionize in water, increasing the effects of all colligative properties. C. The vapor pressure of a solvent decreases as its mole fraction increases. D. The solubility of a gas increases as the temperature decreases. E. The solubility of a gas in solution increases as the pressure of the gas increases. Which of the following solutions would show the greatest conductivity at 30 C? A. 0.20 M Ca(NO 3 ) 2 B. 0.25 M HCl C. 0.20 M NaOH D. 0.10 M NaCl E. 0.40 CH 3 OH A solution of NH 3 dissolved in water is 10.0 m. What is the mole fraction of water in the solution? A. 1.00/1.18 B. 1.00/2.18 C. 0.18/1.00 D. 0.18/10.0 E. 1.18 Answer the following questions to the best of your ability. 4. List the following aqueous solutions in order of their expected freezing points (from lowest to highest): 0.50 m CaCl 2 ; 0.15 m NaCl; 0.10 m HCl; 0.050 m HC 2 H 3 O; 0.10 m C 12 H 22 O 11.
(Questions 5-8) A solution is formed by dissolving 10.0 grams of potassium chloride in 500.0 grams of water. 5. What is the vapor pressure of the solution at 25 C if the vapor pressure of pure water is 23.8 mm Hg at 25 C? 6. What is the boiling-point elevation? K b for water is 0.52 C. kg/mol. 7. What is the freezing-point depression? K f for water is 1.86 C. kg/mol. 8. What is the osmotic pressure of the solution? Assume that the volume of the solution is 0.500 L at 25 C. 9. A solution of an unknown volatile nonelectrolyte was prepared by dissolving 0.250 grams of the substance in 40.0 grams of CCl 4. The boiling point of the resultant solution was 0.357 C higher than that of the pure solvent. Calculate the molar mass of the solute. The K b for CCl 4 is 5.02 C. kg/mol.
10. Lysozyme is an enzyme that breaks bacterial cell walls. A solution containing 0.150 grams of this enzyme in 210 ml of solution has an osmotic pressure of 0.953 torr at 25 C. What is the molar mass of this substance? (Questions 11-12) Carbon disulfide boils at 46.30 C and has a density of 1.26 g/ml. 11. When 0.250 moles of a nondissociating solute is dissolved in 400.0 ml of carbon disulfide, the solution boils at 47.46 C. What is the molal-boiling point elevation constant for carbon disulfide? 12. When 5.39 grams of nondissociating unknown is dissolved in 50.0 ml of carbon disulfide, the solution boils at 47.08 C. What is the molar mass of the unknown? 13. Michael Faraday first prepared ruby-red colloids of gold particles in water that were stable for indefinite times. To the unaided eye these brightly colored colloids are not distinguishable from solutions. How could you determine whether a given colored preparation is a solution or colloid? (Questions 14-15) The osmotic pressure of 0.010 M aqueous solution of calcium chloride is found to be 0.674 atm at 25 C. 14. Calculate the van t Hoff factor for this solution.
15. How would you expect the value of i to change as the solution becomes more concentrated? Explain. 16. What volume of ethylene glycol (C 2 H 6 O 2 ), a nonelectrolyte, must be added to 15.0 L of water to produce an antifreeze solution with a freezing point of -30.0 C? The density of ethylene glycol is 1.11 g/cm 3, and the density of water is 1.00 g/cm 3. The K f = 1.86 C. kg/mol and K b = 0.51 C. kg/mol). a. What is the boiling point of this solution? 17. A solution contains 3.75 grams of a nonvolatile pure hydrocarbon in 95 grams of acetone. The boiling points of pure acetone and the solution are 55.95 C and 56.50 C respectively. The molal boiling point constant of acetone is 1.71 C. kg/mol. What is the molar mass of the hydrocarbon?
(Questions 18-22) Answer the following questions about a pure compound that contains only carbon, hydrogen, and oxygen. 18. A 0.7549 gram sample of the compound burns in O(g) to produce 1.9061 grams of CO 2 (g) and 0.3370 grams of H 2 O(g). Calculate the individual masses of C, H, and O in the 0.7549 gram sample. 19. Determine the empirical formula for the compound. 20. A 0.5246 gram sample of the compound was dissolved in 10.0012 g of lauric acid, and it was determined that the freezing point of the lauric acid was lowered by 1.68 C. The value of K f of lauric acid is 3.90 C m -1. Assume that the compound does not dissociate in lauric acid.. Calculate the molality of the compound dissolved in the lauric acid. 21. Calculate the molar mass of the compound from the information provided. 22. Without doing any calculations, explain how to determine the molecular formula of the compound based on the answers to #20 and #23 above.