Chapter 12 – Physical Properties of Solutions
80. The vapor pressure of water at 45.0 C is 71.93 mmHg. Calculate the vapor pressure of a
solution of 1.50m K2CO3 at this temperature (assume 100% dissociation).
81. The vapor pressure of water at 45.0 C is 71.93 mmHg. Calculate the vapor pressure of a
solution of 1.25m Al(ClO3)3 at this temperature (assume 100% dissociation).
Chapter 12 – Physical Properties of Solutions
82. What is the molarity of a solution that is 5.50 % by mass oxalic acid (C2H2O4) and has a
density of 1.0244 g/mL?
83. 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?
Chapter 12 – Physical Properties of Solutions
84. What is the percent by mass of sodium phosphate in a 0.142 M Na3PO4(aq) solution that
has a density of 1.015 g/mL?
85. What is the molality of a 0.142 M Na3PO4(aq) solution that has a density of 1.015 g/mL?
Chapter 12 – Physical Properties of Solutions
86. What is the mole fraction of sodium phosphate in a 0.142 M Na3PO4(aq) solution that has
a density of 1.015 g/mL?
87. What is the mole fraction of NaOH in a 32.0 % by mass NaOH aqueous solution?
Chapter 12 – Physical Properties of Solutions
88. What is the mass % of K2SO4 in an aqueous solution that has a mole fraction of K2SO4, X
= 0.350?
89. Which of the following concentration units will change with temperature?
Chapter 12 – Physical Properties of Solutions
90. A solution is prepared by adding 6.24 g of benzene (C6H6, 78.11 g/mol) to 80.74 g of
cyclohexane (C6H12, 84.16 g/mol). Calculate the mole fraction and molality of benzene in this
solution.
91. 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.
Chapter 12 – Physical Properties of Solutions
92. 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 10–3
mol/L·atm.
93. The concentration of nitrogen in water at 25C was determined to be 7.2 10–6 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 10–4 mol/L·atm.
Chapter 12 – Physical Properties of Solutions
94.
How many grams of propanol (C3H7OH, 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 L·atm/K·mol)
95.
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 CH3O. 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 of the compound. (R = 0.0821 L·atm/K·mol)
Chapter 12 – Physical Properties of Solutions
96. How many liters of ethylene glycol antifreeze (C2H6O2) 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.)
97. A research chemist isolates a new compound with an empirical formula C3H3O2.
Dissolving 2.51 g of the compound in 100. g of water produces a solution with a freezing
point of –0.325C. What is the molecular formula of the compound? (For water, Kf =
1.86C/m.)
Chapter 12 – Physical Properties of Solutions
98. 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.
99. 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.
Chapter 12 – Physical Properties of Solutions
100. Select True or False: Using your knowledge of osmosis or osmotic pressure decide if the
following statement is true or false: When sprinkled with sugar, a dish of sliced fruit will form
its own juice.
101. Select True or False: Using your knowledge of osmosis or osmotic pressure decide if the
following statement is true or false: Meat that is salted before cooking tends to dry out.
102. Select True or False: Using your knowledge of osmosis or osmotic pressure decide if the
following statement is true or false: In trees and plants water is drawn from the soil up into the
Chapter 12 – Physical Properties of Solutions
103. Select True or False: Using your knowledge of osmosis or osmotic pressure decide if the
following statement is true or false: Drinking salt water actually dehydrates our tissues.
104. 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.]
Chapter 12 – Physical Properties of Solutions
105. Calculate the mass of solute in the following solution: 50.0 mL of 0.0300 M C12H22O11.
106. 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?
Chapter 12 – Physical Properties of Solutions
107. 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?
108. 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)
Chapter 12 – Physical Properties of Solutions
109. List the following solutions in order of increasing boiling point: 0.15m NaI, 0.10m
K3PO4, 0.20 ethylene glycol
110. List the following solutions in order of decreasing melting point: 0.20m glycerol, 0.11m
Sc(NO3)3, 0.15m K2CO3
Chapter 12 – Physical Properties of Solutions
111. Some KCl is dissolved in water at 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%.
112. Plasma is the fluid portion of blood. The concentration of acetylsalicylic acid (aspirin,
C9H8O4, molar mass = 180. g/mol) in your plasma is found to be 2.99 10–4 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.)
Chapter 12 – Physical Properties of Solutions
113. Plasma is the fluid portion of blood. The concentration of acetylsalicylic acid (aspirin,
C9H8O4, molar mass = 180. g/mol) in your plasma is found to be 2.99 10–4 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.)
114. Select True or False: A solution made of pentane and hexane has a mole fraction, X =
115. Select True or False: A solution made of pentane and hexane has a mole fraction, X =
0.250 of pentane. Hexane is the solute.
Chapter 12 – Physical Properties of Solutions
116. Select True or False: The vapor pressure of a solution depends on the chemical nature of
117. Select True or False: The vapor pressure of a solution depends on the chemical nature of
the solvent.
118. Select True or False: To interconvert the concentration units of molarity (M) and mass
percent, you must also know the density of the solution.
Chapter 12 – Physical Properties of Solutions
119. Select True or False: To interconvert the concentration units of molality (m) and mass
120. Select True or False: The solubility of gases in water always decreases with increasing
temperature.
121. Select True or False: For water Kf = 1.86C/m. Therefore, the freezing points of 1.0 M
aqueous KCl and C2H5OH (ethanol) solutions are the same.
Chapter 12 – Physical Properties of Solutions
122. Select True or False: The solubility of a solid always increases with increasing solvent
temperature.