Ch.13 - Solutions & Their Properties
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- Lactose, C12H22O11, is a naturally occurring sugar found in mammalian milk. A 0.335 M solution of lactose in water has a density of 1.0432 g/L at 20 °C. What is the concentra- tion of this solution in the following units? (b) Mass percent
Problem 79
- Look at the solubility graph in Figure 13.7, and estimate which member of each of the following pairs has the higher molar solubility at the given temperature. (b) CH3CO2Na or glucose at 20 °C
Problem 80
- Vinyl chloride (H2C=CHCl), the starting material from which PVC polymer is made, has a Henry’s law constant of 0.091 mol/L-atm at 25 °C. What is the solubility of vinyl chloride in water in mol/L at 25 °C and a partial pressure of 0.75 atm?
Problem 82
- Hydrogen sulfide, H₂S, is a toxic gas responsible for the odor of rotten eggs. The solubility of H₂S in water at STP is 0.195 M. What is the Henry’s law constant of H₂S at 0 °C? What is the solubility of H₂S in water at 0 °C and a partial pressure of 25.5 mm Hg?
Problem 83
- Fish generally need an O2 concentration in water of at least 4 mg/L for survival. What partial pressure of oxygen above the water in atmospheres at 0 °C is needed to obtain this concentration? The solubility of O2 in water at 0 °C and 1 atm partial pressure is 2.21 * 10-3 mol>L.
Problem 84
- At an altitude of 10,000 ft, the partial pressure of oxygen in the lungs is about 68 mm Hg. What is the concentration in mg/L of dissolved O2 in blood (or water) at this partial pres- sure and a normal body temperature of 37 °C? The solubil- ity of O2 in water at 37 °C and 1 atm partial pressure is 1.93 * 10-3 mol>L.
Problem 85
- Sulfur hexafluoride, which is used as a nonflammable insulator in high-voltage transformers, has a Henry’s law constant of 2.4 * 10⁻⁴ mol/L·atm at 25 °C. What is the solubility in mol/L of sulfur hexafluoride in water at 25 °C and a partial pressure of 2.00 atm?
Problem 86
- When 1 mL of toluene is added to 100 mL of benzene (bp 80.1 °C), the boiling point of the benzene solution rises, but when 1 mL of benzene is added to 100 mL of toluene (bp 110.6 °C), the boiling point of the toluene solution falls. Explain.
Problem 88
- When solid CaCl2 is added to liquid water, the temperature rises. When solid CaCl2 is added to ice at 0 °C, the temperature falls. Explain.
Problem 89
- Which of the following aqueous solutions has the (a) higher freezing point, (b) higher boiling point, (c) lower vapor pressure: 0.50 m sucrose (C12H22O11) or 0.35 m HNO3?
Problem 91
- What is the vapor pressure in mm Hg of a solution prepared by dissolving 5.00 g of benzoic acid (C7H6O2) in 100.00 g of ethyl alcohol (C2H6O) at 35 °C? The vapor pressure of pure ethyl alcohol at 35 °C is 100.5 mm Hg.
Problem 92
- What is the freezing point in °C of a solution prepared by dissolving 7.40 g of MgCl2 in 110 g of water if the value of Kf for water is given in Table 13.4, and the van’t Hoff factor for MgCl2 is i = 2.7?
Problem 94
- Assuming complete dissociation, what is the molality of an aqueous solution of KBr whose freezing point is -2.95 °C? The molal freezing-point-depression constant of water is given in Table 13.4.
Problem 95
- When 9.12 g of HCl was dissolved in 190 g of water, the freezing point of the solution was - 4.65 °C. What is the value of the van't Hoff factor for HCl?
Problem 96
- The observed osmotic pressure for a 0.125 M solution of MgCl2 at 310 K is 8.57 atm. Calculate the value of the van’t Hoff factor for MgCl2 under these conditions.
Problem 97
- A solution concentration must be expressed in molality when considering boiling-point elevation or freezing-point depression but can be expressed in molarity when consider- ing osmotic pressure. Why?
Problem 101
- What is the vapor pressure in mm Hg of the following solu-tions, each of which contains a nonvolatile solute? The vapor pressure of water at 45.0 °C is 71.93 mm Hg. (b) A solution of 10.0 g of LiCl in 150.0 g of water at 45.0 °C, assuming complete dissociation
Problem 102
- What is the vapor pressure in mm Hg of a solution of 16.0 g of glucose (C6H12O6) in 80.0 g of methanol (CH3OH) at 27 °C? The vapor pressure of pure methanol at 27 °C is 140 mm Hg.
Problem 103
- What is the freezing point in °C of each of the solutions in Problem 13.102? For water, Kf = 1.86 °C·kg/mol.
Problem 105
- A 1.0 m solution of K2SO4 in water has a freezing point of -4.3 °C. What is the value of the van’t Hoff factor i for K2SO4?
Problem 106
- The van’t Hoff factor for KCl is i = 1.85. What is the boiling point of a 0.75 m solution of KCl in water? For water, Kb = 0.511°C kg/mol.
Problem 107
- Heptane (C₇H₁₆) and octane (C₈H₁₈) are constituents of gasoline. At 80.0 °C, the vapor pressure of heptane is 428 mm Hg, and the vapor pressure of octane is 175 mm Hg. What is the mole fraction of heptane (Xheptane) in a mixture of heptane and octane that has a vapor pressure of 305 mm Hg at 80.0 °C?
Problem 108
- Cyclopentane 1C5H102 and cyclohexane 1C6H122 are vola- tile, nonpolar hydrocarbons. At 30.0 °C, the vapor pres- sure of cyclopentane is 385 mm Hg, and the vapor pressure of cyclohexane is 122 mm Hg. What is Xpentane in a mixture of C5H10 and C6H12 that has a vapor pressure of 212 mm Hg at 30.0 °C?
Problem 109
- The industrial solvents chloroform (CHCl₃) and dichloromethane (CH₂Cl₂) are prepared commercially by the reaction of methane with chlorine, followed by fractional distillation of the product mixture. At 25 °C, the vapor pressure of CHCl₃ is 205 mm Hg, and the vapor pressure of CH₂Cl₂ is 415 mm Hg. What is the vapor pressure in mm Hg at 25 °C of a mixture of 15.0 g of CHCl₃ and 37.5 g of CH₂Cl₂?
Problem 111
- What is the mole fraction of each component in the liquid mixture in Problem 13.110, and what is the mole fraction of each component in the vapor at 30 °C?
Problem 112
- What is the mole fraction of each component in the liquid mixture in Problem 13.111, and what is the mole fraction of each component in the vapor at 25 °C?
Problem 113
- A solution prepared by dissolving 5.00 g of aspirin, C9H8O4, in 215 g of chloroform has a normal boiling point that is elevated by ΔT = 0.47 °C over that of pure chloro- form. What is the value of the molal boiling-point-elevation constant for chloroform?
Problem 114
- A solution prepared by dissolving 3.00 g of ascorbic acid (vitamin C, C6H8O6) in 50.0 g of acetic acid has a freez- ing point that is depressed by ΔT = 1.33 °C below that ofpure acetic acid. What is the value of the molal freezing- point-depression constant for acetic acid?
Problem 115
- A solution of citric acid, C6H8O7, in 50.0 g of acetic acid has a boiling point elevation of ΔT = 1.76 °C. What is the molality of the solution if the molal boilin# g-point-elevation constant for acetic acid is Kb = 3.07 1°C kg2>mol.
Problem 116
- What is the normal boiling point in °C of ethyl alcohol if a solution prepared by dissolving 26.0 g of glucose (C6H12O6) in 285 g of ethyl alcohol has a boiling point of 79.1 °C? See Table 13.4 to find Kb for ethyl alcohol.
Problem 117