Chapter 12
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Chapter 12

Course Number: CHEM161 161, Spring 2011

College/University: Harvard

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Chapter 12: Physical Properties of Solutions 1. A saturated solution A) contains more solute than solvent. B) contains more solvent than solute. C) contains equal moles of solute and solvent. D) contains the maximum amount of solute that will dissolve in that solvent at that temperature. E) contains a solvent with only sigma bonds and no pi bonds (i.e. only single bonds, with no double or triple bonds). Ans: D...

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12: Chapter Physical Properties of Solutions 1. A saturated solution A) contains more solute than solvent. B) contains more solvent than solute. C) contains equal moles of solute and solvent. D) contains the maximum amount of solute that will dissolve in that solvent at that temperature. E) contains a solvent with only sigma bonds and no pi bonds (i.e. only single bonds, with no double or triple bonds). Register to View AnswerCategory: Easy Section: 12.1 2. Which one of the following would be immiscible with water? Register to View AnswerCategory: Medium Section: 12.2 3. Heat of solution A) is never positive ( Hsoln 0), because the solute-solvent attraction is never weaker than the combination of the solute-solute attraction and solvent-solvent attraction. B) is always positive ( Hsoln > 0), because the solute-solvent attraction is always weaker than the combinatio n of the solute-solute attraction and solvent-solvent attraction. C) is always zero (Hsoln = 0), because the solute-solvent attraction is defined as the average of the solute-solute attraction and solvent-solvent attraction. D) is always negative (H soln < 0), because the solute-solvent attraction is always stronger than the combination of the solute-solute attraction and solvent-solvent attraction. E) may be positive, zero, or negative, depending on the relative strength of the solutesolvent, solute-solute, and solvent-solvent attractive forces. Register to View AnswerCategory: Medium Section: 12.1 Page 219 Chapter 12: Physical Properties of Solutions 4. Which response lists all the following pairs that are miscible liquids. Pair #1: octane (C 8 H18 ) and water Pair #2: acetic acid (CH3 COOH) and water Pair #3: octane (C 8 H18 ) and carbon tetrachloride(CCl4 ) A) 1, 3 B) 1, 2 C) 3 D) 2 E) 2, 3 Register to View AnswerCategory: Medium Section: 12.2 5. In which of the following solvents would you expect KBr to be most soluble? A) C6 H14 (hexane) D) CCl4 (carbon tetrachloride) B) CH3 CH2 OH (ethanol) E) C6 H12 (cyclohexane) C) C6 H6 (benzene) Register to View AnswerCategory: Medium Section: 12.2 6. Which of the following liquids would make a good solvent for iodine, I2 ? A) HCl B) H2 O C) CH3 OH D) NH3 E) CS2 Register to View AnswerCategory: Medium Section: 12.2 7. Which of the following compounds should be soluble in CCl4 ? A) NaCl B) H2 O C) NaOH D) C8 H18 E) None of these Register to View AnswerCategory: Medium Section: 12.2 8. A 9.50 % by mass solution of acetone (C 3 H6 O) in water has a density of 0.9849 g/mL at 20C. What is the molarity of this solution? A) 0.621 M B) 1.61 M C) 1.66 M D) 1.71 M E) 16.9 M Register to View AnswerCategory: Medium Section: 12.3 9. A 15.00 % by mass solution of lactose (C 12 H22 O11 , 342.30 g/mol) in water has a density of 1.0602 g/mL at 20C. What is the molarity of this solution? A) 0.03097 M B) 0.4133 M C) 0.4646 M D) 1.590 M E) 3.097 M Register to View AnswerCategory: Medium Section: 12.3 10. A 20.0 % by mass solution of phosphoric acid (H3 PO4 ) in water has a density of 1.114 g/mL at 20C. What is the molarity of this solution? A) 0.0114 M B) 0.0568 M C) 0.114 M D) 2.27 M E) 11.4 M Register to View AnswerCategory: Medium Section: 12.3 11. Which of the following gives the molarity of a 17.0% by mass solution of sodium acetate, CH3 COONa (molar mass = 82.0 g/mol) in water? The density of the solution is 1.09 g/mL. A) 2.26 106 M B) 0.207 M C) 2.07 M D) 2.26 M E) 2.72 M Register to View AnswerCategory: Medium Section: 12.3 Page 220 Chapter 12: Physical Properties of Solutions 12. What is the molarity of a solution of 10% by mass cadmium sulfate, CdSO4 (molar mass = 208.46 g/mol) by mass? The density of the solution is 1.10 g/mL. A) 0.528 M B) 0.436 M C) 0.479 M D) 0.048 M E) 22.9 M Register to View AnswerCategory: Medium Section: 12.3 13. What is the molarity of a solution that is 7.00% by mass magnesium sulfate and has a density of 1.071 g/mL? A) 0.0890 M B) 0.496 M C) 0.543 M D) 0.623 M E) 1.32 M Register to View AnswerCategory: Medium Section: 12.3 14. What is the percent CdSO4 by mass in a 1.0 molal aqueous CdSO4 solution? A) 1.00 103 % B) 0.100 % C) 17.2 % D) 20.8 % E) 24.4 % Register to View AnswerCategory: Medium Section: 12.3 15. Determine the mass percent HCl in a 1.2 M solution of hydrochloric acid with a density of 1.019 g/mL? A) 3.0 % B) 4.3 % C) 8.6 % D) 13% E) 30. % Register to View AnswerCategory: Medium Section: 12.3 16. What is the percent CsCl by mass in a 0.711 M CsCl solution that has a density of 1.091 g/mL? A) 3.87 104 % D) 1.10 % 1 B) 3.87 10 % E) 6.50 102 % C ) 11.0 % Register to View AnswerCategory: Medium Section: 12.3 17. Calculate the percent by mass of potassium nitrate in a solution made from 45.0 g KNO3 and 295 mL of water. The density of water is 0.997 g/mL. A) 1.51 % B) 7.57 % C) 13.3 % D) 15.2 % E) None of these Register to View AnswerCategory: Medium Section: 12.3 18. How many grams of water are needed to dissolve 27.8 g of ammonium nitrate NH4 NO3 in order to prepare a 0.452 m solution? A) 769 g B) 36.2 g C) 100. g D) 0.157 g E) 157 g Register to View AnswerCategory: Medium Section: 12.3 19. In how many grams of water should 25.31 g of potassium nitrate (KNO3 ) be dissolved to prepare a 0.1982 m solution? A) 250.0 g B) 792.0 g C) 1,000. g D) 1,263 g E) 7,917 g Register to View AnswerCategory: Medium Section: 12.3 Page 221 Chapter 12: Physical Properties of Solutions 20. Calculate the molality of a solution containing 14.3 g of NaCl in 42.2 g of water. A) 2.45 104 m D) 103 m 4 B) 5.80 10 m E) 5.80 m C) 2.45 101 m Register to View AnswerCategory: Medium Section: 12.3 21. What is the molality of a solution that is 3.68 % by mass calcium chloride. A) 0.0332 m B) 0.332 m C) 0.344 m D) 0.464 m E) 0.506 m Register to View AnswerCategory: Medium Section: 12.3 22. What is the mass percent CH3 OH of a 0.256 m CH3 OH(aq) solution. A) 0.814 % B) 0.992 % C) 1.23 % D) 1.29 % E) 1.51 % Register to View AnswerCategory: Medium Section: 12.3 23. Calculate the molality of a 20.0% by mass ammonium sulfate (NH4 )2 SO4 solution. The density of the solution is 1.117 g/mL. A) 0.150 m B) 1.51 m C) 1.70 m D) 1.89 m E) 2.10 m Register to View AnswerCategory: Medium Section: 12.3 24. Calculate the molality of 6.0 M H2 SO4 solution. The density of the solution is 1.34 g/mL. A) 4.48 m B) 7.98 m C) 8.10 m D) 8.43 m E) 10.2 m Register to View AnswerCategory: Medium Section: 12.3 25. The density of a 20.3 M CH3 OH (methanol) solution is 0.858 g/mL. What is the molality of this solution? H2 O is the solvent. A) 17.4 m B) 20.8 m C) 23.7 m D) 70.0 m E) 97.6 m Register to View AnswerCategory: Medium Section: 12.3 26. Calculate the molality of a 15.0% by mass solution of MgCl2 in H2 O. The density of this solution is 1.127 g/mL. A) 0.157 m B) 11.8 m C) 1.86 m D) 0.0134 m E) 1.58 m Register to View AnswerCategory: Medium Section: 12.3 27. Which of the following has the greater molal concentration (molality)? A) 1.0 m KNO3 B) 1.0 M KNO3 C) Both have same molality. Register to View AnswerCategory: Medium Section: 12.3 28. The solubility of gases in water usually decreases with A) increasing pressure. B) increasing temperature. C) decreasing temperature. Register to View AnswerCategory: Easy Section: 12.4 Page 222 Chapter 12: Physical Properties of Solutions 29. Oxygen gas makes up 21 % of the atmosphere by volume. What is the solubility of O2 (g) in water at 25C if the atmospheric pressure is 741 mmHg? The Henry's law constant for oxygen gas at 25C is 1.3 103 mol/Latm. A) 2.7 104 M D) 9.6 103 M 3 B) 1.3 10 M E) 0.96 M 3 C) 6.2 10 M Register to View AnswerCategory: Medium Section: 12.5 30. The solubility of nitrogen gas at 25C and a nitrogen pressure of 522 mmHg is 4.7 104 mol/L. What is the value of the Henry's Law constant in mol/Latm? A) 6.8 104 mol/Latm D) 9.0 107 mol/Latm B) 4.7 104 mol/Latm E) 1.5 103 mol/Latm 4 C) 3.2 10 mol/Latm Register to View AnswerCategory: Medium Section: 12.5 31. The solubility of oxygen in lakes high in the Rocky Mountains is affected by the altitude. If the solubility of O2 from the air is 2.67 104 M at sea level and 25C, what is the solubility of O2 at an elevation of 12,000 ft where the atmospheric pressure is 0.657 atm? Assume the temperature is 25C, and that the mole fraction of O2 in air is 0.209 at both 12,000 ft and at sea level. A) 1.75 104 M D) 4.06 104 M B) 2.67 104 M E) None of the above. 5 C) 3.66 10 M Register to View AnswerCategory: Difficult Section: 12.5 32. The solubility of CO2 gas in water A) increases with increasing temperature. B) decreases with decreasing temperature. C) decreases with increasing temperature. D) is not dependent on temperature. Register to View AnswerCategory: Easy Section: 12.4 33. The solubility of CO2 gas in water A) increases with increasing gas pressure. B) increases with decreasing gas pressure. C) decreases with increasing gas pressure. D) is not dependent on pressure. Register to View AnswerCategory: Easy Section: 12.5 34. At 10 C one volume of water dissolves 3.10 volumes of chlorine gas at 1.00 atm pressure. What is the Henry's Law constant in mol/Latm? A) 3.8 B) 0.043 C) 36. D) 3.1 E) 0.13 Register to View AnswerCategory: Difficult Section: 12.5 Page 223 Chapter 12: Physical Properties of Solutions 35. According to Raoult's law, which statement is false? A) The vapor pressure of a solvent over a solution decreases as its mole fraction increases. B) The solubility of a gas increases as the temperature decreases. C) The vapor pressure of a solvent over a solution is less than that of pure solvent. D) The greater the pressure of a gas over a solution the greater its solubility. E) Ionic solutes dissociate in solution causing an enhancement of all colligative properties. Register to View AnswerCategory: Medium Section: 12.6 36. Consider a solution made from a nonvolatile solute and a volatile solvent. Which statement is true? A) The vapor pressure of the solution is always greater than the vapor pressure of the pure solvent. B) The boiling point of the solution is always greater than the boiling point of the pure solvent. C) The freezing point of the solution is always greater than the freezing point of the pure solvent. Register to View AnswerCategory: Medium Section: 12.6 37. The vapor pressure of water at 20C is 17.5 mmHg. What is the vapor pressure of water over a solution prepared from 2.00 102 g of sucrose (C 12 H22O11 ) and 3.50 102 g water? A) 0.51 mmHg D) 18.0 mmHg B) 16.0 mmHg E) 19.4 mmHg C) 17.0 mmHg Register to View AnswerCategory: Difficult Section: 12.6 38. A solution is 40.0% by volume benzene (C 6 H6 ) in carbon tetrachloride at 20C. The vapor pressure of pure benzene at this temperature is 74.61 mmHg and its density is 0.87865 g/cm3 ; the vapor pressure of pure carbon tetrachloride is 91.32 mmHg and its density is 1.5940 g/cm3 . If this solution is ideal, its total vapor pressure at 20C is A) 84.64 mmHg D) 81.63 mmHg B) 84.30 mmHg E) 165.93 mmHg C) 82.96 mmHg Register to View AnswerCategory: Difficult Section: 12.6 39. A solution of carbon tetrachloride in benzene, C6 H6 , at 20C has a total vapor pressure of 78.50 mmHg. (Assume that this solution is ideal.) The vapor pressure of pure benzene at this temperature is 74.61 mmHg and its density is 0.87865 g/cm3 ; the vapor pressure of pure carbon tetrachloride is 91.32 mmHg and its density is 1.5940 g/cm3 . What percentage of the volume of this solution is due to carbon tetrachloride? (Hint: assume that you have 1.000 L of solution.) A) 75.2% B) 76.7% C) 14.3% D) 24.8% E) 23.3% Register to View AnswerCategory: Difficult Section: 12.6 Page 224 Chapter 12: Physical Properties of Solutions 40. A solution of chloroform, CHCl3 , and acetone, (CH3 )2 CO, exhibits a negative deviation from Raoult's law. This result implies that A) chloroform-chloroform interactions are stronger than chloroform-acetone interactions. B) chloroform-chloroform interactions are weaker than chloroform-acetone interactions. C) acetone-acetone interactions are stronger than chloroform-acetone interactions. D) acetone-acetone interactions are weaker than chloroform-acetone interactions. E) Both B and D. F) Both A and C. Register to View AnswerCategory: Medium Section: 12.6 41. Dissolving a solute such as KOH in a solvent such as water results in A) an increase in the melting point of the liquid. B) a decrease in the boiling point of the liquid. C) a decrease in the vapor pressure of the liquid. D) no change in the boiling point of the liquid. Register to View AnswerCategory: Medium Section: 12.7 42. What is the freezing point of a solution that contains 10.0 g of glucose (C 6 H12 O6 ) in 100. g of H2 O? Kf for water is 1.86C/m. A) 0.186C B) +0.186C C) 0.10C D) +0.10C E) 1.03C Register to View AnswerCategory: Medium Section: 12.6 43. Which of the following aqueous solutions has the highest boiling point? Kb for water is 0.52C/m. A) 0.2 m KCl D) A and B. B) 0.2 m Na2 SO4 E) B and C. C) 0.2 m Ca(NO3 )2 Register to View AnswerCategory: Medium Section: 12.7 44. Which of the following aqueous solutions has the highest osmotic pressure at 25C? A) 0.2 M KBr B) 0.2 M ethano l C) 0.2 M Na2 SO4 D) 0.2 M KCl Register to View AnswerCategory: Medium Section: 12.7 45. During osmosis A) pure solvent diffuses through a membrane but solutes do not. B) pure solutes diffuse through a membrane but solvent does not. C) pure solve nt and a solution both diffuse at the same time through a membrane. D) gases diffuse through a membrane into a solution and build up pressure. Register to View AnswerCategory: Medium Section: 12.6 Page 225 Chapter 12: Physical Properties of Solutions 46. Calculate the freezing point of a solution made from 22.0 g of octane (C 8 H18 ) dissolved in 148.0 g of benzene. Benzene freezes at 5.50C and its Kf value is 5.12C/m. A) 1.16C B) 0.98C C) 6.66C D) 12.2C E) 5.49C Register to View AnswerCategory: Medium Section: 12.6 47. What is the freezing point of a solution prepared from 50.0 g ethylene glycol (C 2 H6 O2 ) and 85.0 g H2 O? Kf of water is 1.86C/m. A) 17.6C B) 176C C) 1.50C D) 1.50C E) 17.6C Register to View AnswerCategory: Medium Section: 12.6 48. A solution that contains 55.0 g of ascorbic acid (Vitamin C) in 250. g of water freezes at 2.34C. Calculate the molar mass (in units of g/mol) of the solute. Kf of water is 1.86C/m. A) 1.26 B) 10.9 C) 43.6 D) 175 E) 277 Register to View AnswerCategory: Medium Section: 12.6 49. What is the molar mass of toluene if 0.85 g of toluene depresses the freezing point of 100. g of benzene by 0.47C? Kf of benzene is 5.12C/m. A) 92.6 g/mol B) 78.0 g/mol C) 10.7 g/mol D) 81.8 g/mol E) 927 g/mol Register to View AnswerCategory: Medium Section: 12.6 50. What mass of ethanol, C2 H5 OH a nonelectrolyte, must be added to 10.0 L of water to give a solution that freezes at 10.0C? Assume the density of water is 1.0 g/mL. Kf of water is 1.86C/m. A) 85.7 kg B) 24.8 kg C) 5.38 kg D) 2.48 kg E) 1.17 kg Register to View AnswerCategory: Medium Section: 12.6 51. When 24.0 g of glucose (a nonelectrolyte) are dissolved in 500. g of water, the solution has a freezing point of 0.47C. What is the molar mass of glucose? Kf of water is 1.86C/m. A) 41.9 g B) 47.5 g C) 54.9 g D) 178 g E) 190. g Register to View AnswerCategory: Medium Section: 12.6 52. What is the osmotic pressure of a solution that contains 13.7 g of propyl alcohol (C 3 H7 OH) dissolved in enough water to make 500. mL of solution at 27C? A) 0.014 atm B) 0.037 atm C) 0.456 atm D) 0.01 atm E) 11.2 atm Register to View AnswerCategory: Medium Section: 12.6 53. What is the freezing point of an aqueous solution of a nonvolatile solute that has a boiling point of 102.5C? For water Kf = 1.86C/m and Kb = 0.52C/m. A) 8.94C B) 366C C) 0.99C D) 0.99C E) 8.94C Register to View AnswerCategory: Medium Section: 12.6 Page 226 Chapter 12: Physical Properties of Solutions 54. What volume of ethanol (density = 0.7893 g/cm3 ) should be added to 450. mL of water in order to have a solution freezes that at 15.0C? (For water, Kf = 1.86 C/m.) A) 371 mL B) 470 mL C) 212 mL D) 132 mL E) 167 mL Register to View AnswerCategory: Medium Section: 12.6 55. What volume of water should be added to 600. mL of ethanol in order to have a solution that boils at 95.0C? (For ethanol, Kb = 1.22 C/m, density = 0.789 g/cm3 , boiling point = 78.4C) A) 186 mL B) 245 mL C) 518 mL D) 116 mL E) 322 mL Register to View AnswerCategory: Medium Section: 12.6 56. Pure benzene, C6 H6 , freezes at 5.5 and boils at 80.1C. What is the boiling point of a solution consisting of cyclohexane (C 6 H12 ) dissolved in benzene if the freezing point of this solution is 0.0C? (For benzene, Kf = 5.12 C/m, Kb = 2.53 C/m; for cyclohexane, Kf = 20.0 C/m, Kb = 2.79C/m) A) 82.8C B) 91.2C C) 80.9C D) 77.4C E) 83.1C Register to View AnswerCategory: Medium Section: 12.6 57. When 12.1 g of the sugar sucrose (a nonelectrolyte) are dissolved in exactly 800 g of water, the solution has a freezing point of 0.082C. What is the molar mass of sucrose? Kf of water is 1.86C/m. A) 426 g B) 99.2 g C) 178 g D) 266 g E) 343 g Register to View AnswerCategory: Medium Section: 12.6 58. What is the osmotic pressure of a 0.25 M solution of sucrose at 37C? (R = 0.0821 Latm/K mol) A) 6.6 105 atm B) 0.76 atm C) 6.4 atm D) 100 atm E) 940 atm Register to View AnswerCategory: Medium Section: 12.6 59. How many grams of sucrose (C 12 H22 O11 , 342.3 g/mol) would be needed to make 2.5 L of a solution with an osmotic pressure of 14 atm at 25C? (R = 0.0821 Latm/K mol) A) 0.57 g B) 6.8 g C) 2.0 102 g D) 4.9 102 g E) 5.8 103 g Register to View AnswerCategory: Medium Section: 12.6 60. What is the boiling point of an aqueous solution of a nonelectrolyte that has an osmotic pressure of 10.50 atm at 25C? Kb of water is 0.52C/m. Assume the density of the solution is the same as that of pure water. A) 0.22C B) 0.429C C) 100.43C D) 99.78C E) 100.22C Register to View AnswerCategory: Difficult Section: 12.6 Page 227 Chapter 12: Physical Properties of Solutions 61. 0.102 g of an unknown compound dissolved in 100. mL of water has an osmotic pressure of 28.1 mmHg at 20C. Calculate the molar mass of the compound. A) 663 g/mol D) 727 g/mol B) 0.872 g/mol E) 1.10 102 g/mol C) 1.15 g/mol Register to View AnswerCategory: Medium Section: 12.6 62. An aqueous dextrose solution having a density of 1.04 g/cm3 freezes at 1.15C. Find the osmotic pressure of this solution at 25C. Kf of water is 1.86 C/m; molecular mass of dextrose = 180.16 g/mol. A) 13.8 atm B) 14.1 atm C) 15.1 atm D) 12.9 atm E) 120 atm Register to View AnswerCategory: Difficult Section: 12.6 63. An aqueous fructose solution having a density of 1.049 g/cm3 is found to have an osmotic pressure of 17.0 atm at 25C. Find the temperature at which this solution freezes. [Given: for water Kf = 1.86 C/m; molecular mass of fructose = 180.16 g/mol] A) 1.52C B) 1.30C C) 1.57C D) 1.69C E) 1.41C Register to View AnswerCategory: Difficult Section: 12.6 64. Consider a 0.90 M Al(NO3 )3 solution. This solution has a nitrate ion concentration of A) 0.30 M B) 0.90 M C) 0.0 M D) 8.1 M E) 2.7 M Register to View AnswerCategory: Easy Section: 12.7 65. What is the approximate Na+ ion concentration in a 0.75 M Na2 CO3 solution? A) 0.375 M B) 0.75 M C) 1.25 M D) 1.50 M E) 2.25 M Register to View AnswerCategory: Easy Section: 12.7 66. Calculate the approximate freezing point of a solution made from 21.0 g NaCl and 1.00 102 g of H2 O. [K f of water is 1.86C/m.] A) 3.59C B) 6.68C C) 13.4C D) 6.68C E) 3.59C Register to View AnswerCategory: Medium Section: 12.7 67. What is the osmotic pressure of a solution prepared from 13.7 g of the electrolyte HCl and enough water to make 0.500 L of solution at 18C? A) 0.55 atm B) 1.10 atm C) 8.95 atm D) 17.9 atm E) 35.9 atm Register to View AnswerCategory: Difficult Section: 12.7 68. Which of the following aqueous solutions has the lowest freezing point? A) 0.18 m KCl D) pure water B) 0.15 m Na2 SO4 E) 0.20 m C2 H6 O2 (ethylene glycol) C) 0.12 m Ca(NO3 )2 Register to View AnswerCategory: Medium Section: 12.7 Page 228 Chapter 12: Physical Properties of Solutions 69. Arrange the following aqueous solutions in order of increasing boiling points: 0.050 m Mg(NO3 )2 ; 0.100 m ethanol; 0.090 m NaCl. A) Mg(NO3 )2 < NaCl < ethanol D) NaCl < ethanol < Mg(NO3 )2 B) ethanol < Mg(NO3 )2 < NaCl E) Mg(NO3 )2 < ethanol < NaCl C) ethanol < NaCl < Mg(NO3 )2 Register to View AnswerCategory: Medium Section: 12.7 70. The osmotic pressure of a 0.010 M MgSO4 solution at 25C is 0.318 atm. Calculate i, the van't Hoff factor, for this MgSO4 solution. A) 0.013 B) 1.3 C) 1.5 D) 2.0 E) 76.8 Register to View AnswerCategory: Medium Section: 12.7 71. What is the molarity of a solution that is 5.50 % by mass oxalic acid (C 2 H2 O4 ) and has a density of 1.0244 g/mL? Ans: 0.626 M Category: Medium Section: 12.3 72. What is the molarity and molality of a solution that is 10.00 % by mass potassium hydrogen carbonate (KHCO3 , 100.11 g/mol) and has a density of 1.0650 g/mL? Ans: 1.064 M and 1.110 m Category: Medium Section: 12.3 73. What is the percent by mass of sodium phosphate in a 0.142 M Na3 PO4 (aq) solution that has a density of 1.015 g/mL? Ans: 2.29 % Category: Medium Section: 12.3 74. What is the molality of a 0.142 M Na3 PO4 (aq) solution that has a density of 1.015 g/mL? Ans: 0.143 m Category: Medium Section: 12.3 75. What is the mole fraction of sodium phosphate in a 0.142 M Na3 PO4 (aq) solution that has a density of 1.015 g/mL? Ans: 0.00257 Category: Medium Section: 12.3 76. Which of the following concentration units will not change with temperature: molarity, percent mass, mole fraction, and molality. Ans: Percent mass, mole fraction, and molality will not change with temperature. Category: Medium Section: 12.3 Page 229 Chapter 12: Physical Properties of Solutions 77. A solution is prepared by adding 6.24 g of benzene (C 6 H6 , 78.11 g/mol) to 80.74 g of cyclohexane (C 6 H12 , 84.16 g/mol). Calculate the mole fraction and molality of benzene in this solution. Ans: mole fraction = 0.0769; molality = 0.989 m Category: Medium Section: 12.3 78. A solution is prepared by adding 40.3 g of Mg(NO3 )2 to 127 g of water. Calculate the mole fraction and molality of magnesium nitrate in this solution. Ans: mole fraction = 0.0371; molality = 2.14 m Category: Medium Section: 12.3 79. What is the concentration of O2 (g) in water at 25C exposed to a partial pressure of oxygen of 325 mmHg? The Henry's law constant for oxygen gas at 25C is 1.3 103 mol/Latm. Ans: 5.6 104 M Category: Medium Section: 12.3 80. The concentration of nitrogen in water at 25C was determined to be 7.2 106 M. Calculate the partial pressure of nitrogen at the surface of the water in mmHg. The Henry's law constant for nitrogen gas at 25C is 6.8 104 mol/Latm? Ans: 8.0 mmHg Category: Medium Section: 12.3 81. How many grams of propanol (C 3 H7 OH, 60.10 g/mol) would be needed to make 750 mL of a solution with an osmotic pressure of 25 atm at 25C? (R = 0.0821 Latm/K mol) Ans: 46 g Category: Medium Section: 12.6 82. An organic compound was prepared and purified by chromatography. A conductivity measurement showed the compound to be a nonelectrolyte. Elemental analysis gave an empirical formula of CH3 O. A 0.127 g sample of the compound was dissolved in water and diluted to 100.0 mL, and the osmotic pressure of that solution was determined to 0.492 atm at 20C. Determine the molar mass and molecular formula of the compound. (R = 0.0821 Latm/K mol) Ans: 62.1 g/mol, consistent with C2 H6 O2 Category: Difficult Section: 12.6 83. How many liters of ethylene glycol antifreeze (C 2 H6 O2 ) would you add to your car radiator containing 15.0 L of water if you needed to protect your engine to 17.8C? (The density of ethylene glycol is 1.1 g/mL. For water, Kf = 1.86C/m.) Ans: 8.1 L Category: Difficult Section: 12.6 Page 230 Chapter 12: Physical Properties of Solutions 84. In the course of research, a chemist isolates a new compound with an empirical formula C3 H3O2 . Dissolving 2.51 g of the compound in 100. g of water produces a solution with a freezing point of 0.325 C. What is the molecular formula of the compound? (For water, Kf = 1.86C/m.) Ans: C6 H6O4 Category: Difficult Section: 12.6 85. Define solvation. Ans: Solvation is the process in which an ion or a molecule is surrounded by solvent molecules arranged in a specific manner. Category: Easy Section: 12.2 86. Automobile radiators usually carry a sticker that indicates that they must contain an antifreeze solution for proper operation, winter or summer. Why should you not use ordinary water during the summer? Ans: The antifreeze will lower the vapor pressure of the fluid or elevate the boiling point of the radiator solution so that the cooling system of your car will be able to operate at higher temperatures without generating excessive pressure. Category: Medium Section: 12.6 87. A 100.-mL sample of water is taken from the Pacific Ocean, and the water is allowed to evaporate. The salts that remain (mostly NaCl) have a mass of 3.85 g. Calculate the original concentration of NaCl, in g per liter, in the water sample. Ans: 38.5 g/L Category: Easy Section: 12.3 88. A 100. mL sample of water is taken from the Great Salt Lake, and the water is allowed to evaporate. The salts that remain (mostly NaCl) have a mass of 31.9 g Calculate the original concentration of NaCl, in g per liter, in each water sample. Ans: 319 g/L Category: Easy Section: 12.3 89. The solubility of oxygen in water is about 4.5 102 g/L. The water portion of an adult's total blood supply is about 5 liters. How many grams of oxygen could dissolve in 5 liters of water? Ans: 0.2 g Category: Easy Section: 12.5 90. It has been suggested that gold might be recovered from seawater. If seawater contains about 4.0 109 g/L of dissolved gold, how many liters of seawater would have to be processed to get 1.00 ounce of gold? (1 oz = 28.4 g) Ans: 7.1 109 L Category: Medium Section: 12.3 Page 231 Chapter 12: Physical Properties of Solutions 91. Explain the following, on the basis of osmosis or osmotic pressure: When sprinkled with sugar, a dish of sliced fruit will form its own juice. Ans: The water inside the fruit cells passes through cell membranes, trying to dilute the sugar on the outside. Category: Medium Section: 12.6 92. Explain the following, on the basis of osmosis or osmotic pressure: Meat that is salted before cooking tends to dry out. Ans: The water passes through the muscle cells to the outside, trying to dilute the salt. Category: Medium Section: 12.6 93. Explain the following, on the basis of osmosis or osmotic pressure: In trees and plants water is drawn from the soil up into the branches and leaves. Ans: The water passes into the cells, which are more concentrated in solutes, and is drawn up the tree by osmosis. Category: Medium Section: 12.6 94. Explain the following, on the basis of osmosis or osmotic pressure: An effective way to kill a snail or slug in your garden is to sprinkle it with salt. Ans: The water leaves the snails cells to dilute the salt, and the snail becomes dehydrated and dies. Category: Medium Section: 12.6 95. Explain the following, on the basis of osmosis or osmotic pressure: Drinking salt water actually dehydrates our tissues. Ans: The water passes from cells, trying to dilute the salt water. Category: Medium Section: 12.6 96. Maple syrup is mostly a solution of sucrose in water. Calculate the molality of the syrup if a sample freezes at 0.50C, assuming the solute is pure sucrose. [For water, Kf is 1.86C/m.] Ans: 0.27 m Category: Medium Section: 12.6 97. Calculate the mass of solute in the following solution: 50.0 mL of 0.0300 M C12 H22 O11 . Ans: 0.513 g Category: Medium Section: 12.3 98. Thyroxine, an important hormone that controls the rate of metabolism in the body, can be isolated from the thyroid gland. If 0.455 g of thyroxine is dissolved in 10.0 g of benzene, the freezing point of the solution is 5.144C. Pure benzene freezes at 5.444C and has a Kf of 5.12C/m. What is the molar mass of thyroxine? Ans: 777 g/mol Category: Difficult Section: 12.6 Page 232 Chapter 12: Physical Properties of Solutions 99. When 20.0 grams of an unknown compound are dissolved in 500. grams of benzene, the freezing point of the resulting solution is 3.77C. The freezing point of pure benzene is 5.444C, and the Kf for benzene is 5.12C/m. What is the molar mass of the unknown compound? Ans: 120 g/mol Category: Difficult Section: 12.6 100. The term "proof" is defined as twice the percent by volume of pure ethanol in solution. A solution that is 95% ethanol is 190 proof. What is the molarity of ethanol in a 92-proof ethanol/water solution? (Given: density of ethanol = 0.80 g/cm3 ; density of water = 1.0 g/cm3 ) Ans: 8.0 M Category: Difficult Section: 12.3 101. Some KCl is dissolved in water 25C, where it completely dissociates. The vapor pressure of pure water at 25C is 28.3 mmHg. On the graph below, sketch the vapor pressure above the salt solution as a function of the mole fraction of H2 O, assuming that Raoult's law is obeyed. Explain how you arrived at your graph. Ans: Pure water has a vapor pressure of 28.3 mmHg and pure KCl has a vapor pressure of zero. Since Raoult's law is obeyed, the line is straight. Category: Medium Section: 12.6 Page 233 Chapter 12: Physical Properties of Solutions 102. Some KCl is dissolved in water 25C, where it completely dissociates. The vapor pressure of pure water at 25C is 28.3 mmHg. Estimate the mass in grams of KCl needed per liter of pure water to reduce the vapor pressure of water at 25C by 5%. Ans: 110 g Category: Difficult Section: 12.6 103. Plasma is the fluid portion of blood. The concentration of acetylsalicylic acid (aspirin, C9 H8O4 , molar mass = 180. g/mol) in your plasma is found to be 2.99 104 M after you take two tablets of aspirin. If the volume of your plasma is 5.85 L, how many grams of aspirin are in your blood? (Assume that the density of plasma is 1.00 g/mL.) Ans: 0.315 g Category: Medium Section: 12.3 104. Plasma is the fluid portion of blood. The concentration of acetylsalicylic acid (aspirin, C9 H8O4 , molar mass = 180. g/mol) in your plasma is found to be 2.99 104 M after you take two tablets of aspirin. If the volume of your plasma is 5.85 L, what is the molality, m, of aspirin in your blood? (Assume density of plasma is 1.00 g/mL.) Ans: 2.99 104 m Catego ry: Medium Section: 12.3 105. For dilute aqueous solutions, the concentration units molarity and molality have almost the same values. Register to View AnswerCategory: Medium Section: 12.3 106. To interconvert the concentration units molarity (M) and mass percent, you must also know the density of the solution. Register to View AnswerCategory: Medium Section: 12.3 107. To interconvert the concentration units molality (m) and mass percent, you must also know the density of the solution. Register to View AnswerCategory: Medium Section: 12.3 108. The solubility of gases in water always decreases with increasing temperature. Register to View AnswerCategory: Easy Section: 12.4 109. For water Kf = 1.86C/m. Therefore, the freezing points of 1.0 M aqueous KCl and C2 H5OH (ethanol) solutions are the same. Register to View AnswerCategory: Medium Section: 12.6 110. The solubility of a solid always increases with increasing solvent temperature. Register to View AnswerCategory: Medium Section: 12.4 Page 234
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