7.49.Estimate the osmotic pressure, freezing point, and boil-
ing point of seawater, which you can approximate as equiva-
lent to a 1.08-molal solution of NaCl. Use equations 7.47 and
7.49 to calculate Kfand Kbfor H 2 O, and use (^) fusH[H 2 O]
6.009 kJ/mol and (^) vapH[H 2 O] 40.66 kJ/mol. From what you
know about seawater, what assumptions are we making?
7.50.Calculate the freezing point depression of mercury
caused by dissolved sodium if the mole fraction of Na is 0.0477.
The normal freezing point of Hg is 39°C and its heat of fu-
sion is 2331 J/mol.
7.51.Use the system in exercise 7.45 to calculate the osmotic
pressure of the mercureous solution of sodium at 0°C. Assume
a volume of 15.2 cm^3.
7.52.Use the system in exercise 7.45 to calculate the vapor
pressure depression of mercury from the solution. The normal
vapor pressure of Hg at 0°C is 0.000185 torr.
7.53.Calculate the cryoscopic and ebullioscopic constants for
liquid bromine, Br 2. You will need the following data:
(^) fusH: 10.57 kJ/mol MP: 7.2°C
(^) vapH: 29.56 kJ/mol BP: 58.78°C
7.54.A 200,000-amu average molecular weight polymer is
contaminated with 0.5% of a 100-amu impurity, presumably
the monomer. Determine the error in the molecular weight
determination if a 1.000 10 ^4 molal aqueous solution is
used. Assume a temperature of 25.0°C.
7.55.Consider an aqueous solution of a polymer that has an
average molecular weight of 185,000 amu. Calculate the mo-
lality that is needed to exert an osmotic pressure of 30 Pa at
37°C. How many grams per kilogram of solvent is this?
7.56.Derive equation 7.49.
7.57.The vapor pressures of benzene and 1,1-dichloroethane
at 25.0°C are 94.0 and 224.9 mmHg, respectively. Plot the
total pressure versus the mole fraction of benzene in the solu-
tion.Plot the total pressure versus the mole fraction of 1,1-
dichloroethane.
7.58.The vapor pressures of benzene and 1,1-dichloroethane
at 25.0°C are 94.0 and 224.9 mmHg, respectively. What does
a plot of total pressure versus the mole fraction of benzene in
the vaporlook like? What does a plot of total pressure versus
the mole fraction of 1,1-dichloroethane look like? Compare
these plots with your plots from exercise 7.57.
7.59.Consider your plots from 7.57 and 7.58 above. (a)
Identify the dew point line(s). (b)Identify the bubble point
line(s). (c)Using a combination of two appropriate lines, trace
the fractional distillation of a 5050 mole ratio of benzene and
1,1-dichloroethane, draw the theoretical plates, and predict
the composition of the initially distilled product.
7.60.Tabulate the solubility of naphthalene in toluene be-
tween 50°C and 70°C in 5° increments. The heat of fusion
of C 10 H 8 is 19.123 kJ/mol and its melting point is 78.2°C.
Exercises for Chapter 7 205
Symbolic Math Exercises