12.69 Which of the following aqueous solutions has (a)
the higher boiling point, (b) the higher freezing point, and
(c) the lower vapor pressure: 0.35 m CaCl2 or 0.90 m
urea? Explain. Assume CaCl2 to undergo complete
dissociation.
12.70 Consider two aqueous solutions, one of sucrose
(C12H22O11) and the other of nitric acid (HNO3). Both
solutions freeze at −1.5°C. What other properties do
these solutions have in common?
12.71 Arrange the following solutions in order of
decreasing freezing point: 0.10 m Na3PO4, 0.35 m NaCl,
0.20 m MgCl2, 0.15 m C6H12O6, 0.15 m CH3COOH.
12.72 Arrange the following aqueous solutions in order
of decreasing freezing point, and explain your reasoning:
0.50 m HCl, 0.50 m glucose, 0.50 m acetic acid.
12.73 What are the normal freezing points and boiling
points of the following solutions? (a) 21.2 g NaCl in 135
mL of water and (b) 15.4 g of urea in 66.7 mL of water
12.74 At 25°C the vapor pressure of pure water is 23.76
mmHg and that of seawater is 22.98 mmHg. Assuming
that seawater contains only NaCl, estimate its molal
concentration.
12.75 Both NaCl and CaCl2 are used to melt ice on roads
and sidewalks in winter. What advantages do these
substances have over sucrose or urea in lowering the
freezing point of water?
12.76 A 0.86 percent by mass solution of NaCl is called
“physiological saline” because its osmotic pressure is
equal to that of the solution in blood cells. Calculate the
osmotic pressure of this solution at normal body
temperature (37°C). Note that the density of the saline
solution is 1.005 g/mL.
12.82 Water and methanol are miscible with each other
but they are immiscible with octane (C8H18). Which of the
following shows the correct picture when equal volumes
of these three liquids are mixed in a test tube at 20°C?
Assume volumes to be additive. (The densities of the
liquids are methanol: 0.792 g/mL; octane: 0.703 g/mL;
water: 0.998 g/mL.)
12.83 Lysozyme is an enzyme that cleaves bacterial cell
walls. A sample of lysozyme extracted from egg white has
a molar mass of 13,930 g. A quantity of 0.100 g of this
enzyme is dissolved in 150 g of water at 25°C. Calculate
the vapor-pressure lowering, the depression in freezing
point, the elevation in boiling point, and the osmotic
pressure of this solution. (The vapor pressure of water at
25°C is 23.76 mmHg.)
12.84 Solutions A and B have osmotic pressures of 2.4
atm and 4.6 atm, respectively, at a certain temperature.
What is the osmotic pressure of a solution prepared by
mixing equal volumes of A and B at the same
temperature?
12.85 A cucumber placed in concentrated brine (salt
water) shrivels into a pickle. Explain.
12.86 Two liquids A and B have vapor pressures of 76
mmHg and 132 mmHg, respectively, at 25°C. What is the
total vapor pressure of the ideal solution made up of (a)
1.00 mole of A and 1.00 mole of B and (b) 2.00 moles of
A and 5.00 moles of B?
12.87 Calculate the van't Hoff factor of Na3PO4 in a 0.40
m solution whose freezing point is −2.6°C.
12.88 A 262-mL sample of a sugar solution containing
1.22 g of the sugar has an osmotic pressure of 30.3
mmHg at 35°C. What is the molar mass of the sugar?
12.89 An aqueous solution of a 0.10 M monoprotic acid
HA has an osmotic pressure of 3.22 atm at 25°C. What is
the percent ionization of the acid at this concentration?
12.90 Calculate the mass of naphthalene (C10H8) that
must be added to 250 g of benzene (C6H6) to give a
solution with a freezing point 2.00°C below that of pure
benzene.