PX-III Chem 1411 Chaps 11 & 12 Ebbing 1. What is the name for the following phase change? I 2 (s) I 2 (g) A) melting B) condensation C) sublimation D) freezing E) vaporization 2. Which of the following processes is exothermic? A) sublimation B) vaporization C) melting D) fusion E) deposition 3. The process represented by the equation C 10 H 8 (s) C 10 H 8 (g) is A) fusion. B) melting. C) sublimation. D) liquefaction. E) condensation. 4. The normal boiling point of a liquid is A) the only temperature at which there can be equilibrium between the liquid and gas states. B) the temperature above which the substance cannot exist as a liquid regardless of the pressure. C) the temperature at which the amounts of liquid and gas are equal. D) the temperature at which the vapor pressure equals atmospheric pressure. E) the temperature at which all three phases are in equilibrium. 5. The enthalpy of fusion of sulfur (S atoms) is 17.7 kj/mol. How many grams of sulfur can be melted by 22.5 kj of energy? A) 9.8 g B) 19.5 g C) 26.2 g D) 40.7 g E) 52.5 g Page 1
6. How much heat is released at constant pressure if a 15.0-L tank containing 80.0 atm of hydrogen sulfide gas condenses at its boiling point of -60.0 o C? The enthalpy of vaporization of hydrogen sulfide is 18.7 kj/mol at -60.0 o C. (R = 0.0821 L atm/(k mol)) A) 1.28 10 6 J B) 1.87 10 4 J C) 2.73 10 2 J D) 4.56 10 6 J E) 7.68 10 1 J 7. The vapor pressure of a given liquid will increase if A) the liquid is moved to a container in which its surface is very much larger. B) the volume of the liquid is increased. C) the volume of the vapor phase is increased. D) the temperature is increased. E) a more volatile liquid is added to the given liquid. 8. A liquid has an enthalpy of vaporization of 30.3 kj/mol. At 272 K it has a vapor pressure of 103 mmhg. What is the normal boiling point of this liquid? (R = 8.31 J/(K mol)) A) 272 K B) 320 K C) 291 K D) 237 K E) 255 K 9. Knowing that H vap for water is 40.7 kj/mol, calculate P vap of water at 37 C. A) 6.90 torr B) 12.4 torr C) 18.7 torr D) 25.4 torr E) 52.6 torr Page 2
10. Choose the correct statement about the diagram below. A) The diagram is qualitatively correct for water. B) The diagram shows that the melting point of the solid increases with increasing pressure. C) The diagram shows the triple point above 1 atm pressure. D) The diagram could represent the phase diagram of CO 2. E) None of the above statements is correct. 11. From a consideration of the phase diagram below, a change from point M to point N corresponds to A) sublimation. B) condensation. C) evaporation. D) freezing. E) liquefaction. 12. The measure of the resistance to flow of a liquid is A) van der Waals forces. B) vapor pressure. C) London forces. D) surface tension. E) viscosity. Page 3
13. The solubility of 1-pentanol in water is 2.7 g per 100 g of water at 25 C. What is the maximum amount of 1-pentanol that will dissolve in 2.5 g of water at 25 C? A) 2.7 g B) 6.8 g C) 0.068 g D) 1.1 g E) 0.011 g 14. The solubility of O 2 in water is 0.590 g/l at an oxygen pressure of around 15.3 atm. What is the Henry's law constant for O 2 (in units of L atm/mol)? A) 3.86 10-2 B) 1.21 10-3 C) 8.30 10 2 D) 2.82 10-1 E) None of the above are within 5% of the correct answer. 15. Which of the following is not a colligative property? A) osmotic pressure B) vapor pressure lowering C) freezing-point depression D) lattice energy E) boiling-point elevation 16. As the number of solute particles in a given volume of solution increases, A) the freezing point will increase and the vapor pressure will increase. B) the freezing point will decrease and the vapor pressure will decrease. C) the boiling point will increase and the vapor pressure will increase. D) the boiling point will decrease and the vapor pressure will decrease. E) the osmotic pressure will decrease and the lattice energy will increase. 17. What mass of 20.0% potassium chloride solution contains 80.0 g of water? A) 20.0 g B) 40.0 g C) 60.0 g D) 80.0 g E) 100.0 g Page 4
18. What is the mass percent of an aqueous sodium hydroxide solution in which the mole fraction of NaOH is 0.311? The density of the solution is 1.5290 g/ml. A) 68.9% B) 47.5% C) 8.12% D) 50.0% E) 4.92% 19. The molality of a solution is defined as A) moles of solute per liter of solution. B) grams of solute per liter of solution. C) moles of solute per kilogram of solution. D) moles of solute per kilogram of solvent. E) the gram molecular weight of solute per kilogram of solvent. 20. The molarity of a solution is the A) moles of solute per liter of solvent. B) moles of solute per kilogram of solution. C) moles of solute per liter of solution. D) moles of solute per kilogram of solvent. E) moles of solute per mole of solution. 21. If 11.7 g of naphthalene, C 10 H 8, is dissolved in 117.1 g of chloroform, CHCl 3, what is the molality of the solution? A) 0.0914 m B) 0.0932 m C) 0.781 m D) 11.9 m E) 0.0908 m 22. What is the mole fraction of urea, CH 4 N 2 O, in an aqueous solution that is 46% urea by mass? A) 0.20 B) 0.80 C) 0.45 D) 0.74 E) 0.46 Page 5
23. What is the vapor pressure at 20 C of an ideal solution prepared by the addition of 5.64 g of the nonvolatile solute urea, CO(NH 2 ) 2, to 22.1 g of methanol, CH 3 OH? The vapor pressure of pure methanol at 20 C is 89.0 mmhg. A) 10.7 mmhg B) 70.9 mmhg C) 60.2 mmhg D) 28.8 mmhg E) 78.3 mmhg 24. What is the freezing point of a 0.21 m solution of glucose, C 6 H 12 O 6, in water? (K f for water is 1.858 C/m.) A) 0.39 C B) 0.20 C C) 0.20 C D) 0.39 C E) 0.78 C 25. When a 41.4-g sample of an unknown compound is dissolved in 500. g of benzene, the freezing point of the resulting solution is 3.77 C. The freezing point of pure benzene is 5.48 C, and K f for benzene is 5.12 C/m. Calculate the molar mass of the unknown compound. A) 124.0 g/mol B) 24.2 g/mol C) 212 g/mol D) 496 g/mol E) 248. g/mol 26. A red blood cell placed in pure water will swell because A) the osmotic pressure is greater in the water than in the cell. B) the osmotic pressure is greater in the cell than in the water. C) the osmotic pressure is the same in the cell and the water. D) water moves from a higher osmotic pressure to a lower osmotic pressure. E) the vapor pressure of the water in the cell is greater than the vapor pressure of pure water. Page 6
27. Determine the osmotic pressure of a solution that contains 0.035 g of a hydrocarbon solute (molar mass = 340 g/mol) dissolved in benzene to make a 350-mL solution. The temperature is 20.0 C. A) 0.37 torr B) 1.8 torr C) 2.4 torr D) 5.4 torr E) 5.0 torr 28. A 2.8-g sample of a small protein having a molecular weight of 42,000 g/mol is dissolved in 45.6 ml of water at 25 C. What is the osmotic pressure of the solution? (R = 0.0821 L atm/(k mol)) A) 0.036 mmhg B) 2.3 mmhg C) 27 mmhg D) 21000 mmhg E) 1100 mmhg 29. Osmotic pressure is A) inversely proportional to mole fraction. B) inversely proportional to mass fraction. C) inversely proportional to molality. D) directly proportional to molarity. E) directly proportional to lattice energy. 30. Calculate the molecular weight of a small protein if a 0.24-g sample dissolved in 196 ml of water has an osmotic pressure of 9.8 mmhg at 23 C. (R = 0.0821 L atm/(k mol)) A) 3.0 10 3 g/mol B) 2.3 10 3 g/mol C) 3.3 10 2 g/mol D) 1.8 10 2 g/mol E) 3.0 g/mol Page 7
Answer Key 1. C 2. E 3. C 4. D 5. D 6. A 7. D 8. B 9. E 10. B 11. D 12. E 13. C 14. C 15. D 16. B 17. E 18. D 19. D 20. C 21. C 22. A 23. E 24. D 25. E 26. B 27. D 28. C 29. D 30. B Page 8