Exercises 587Boiling Point Elevation and Freezing Point
Depression: Solutions of Electrolytes
*063.What is ion association in solution? Can you suggest why
the term “ion pairing” is sometimes used to describe this
phenomenon?
*064.You have separate 0.10 Maqueous solutions of the fol-
lowing salts: LiNO 3 , Ca(NO 3 ) 2 , and Al(NO 3 ) 3. In which
one would you expect to find the highest particle con-
centration? Which solution would you expect to conduct
electricity most strongly? Explain your reasoning.
*065.What is the significance of the van’t Hoff factor, i?
*066.What is the value of the van’t Hoff factor, i,for the
following strong electrolytes at infinite dilution?
(a) Na 2 SO 4 ; (b) KOH; (c) Al 2 (SO 4 ) 3 ; (d) SrSO 4.
*067.Compare the number of solute particles that are present
in solutions of equal concentrations of strong electrolytes,
weak electrolytes, and nonelectrolytes.
*068.Four beakers contain 0.010 m aqueous solutions of
CH 3 OH, KClO 3 , CaCl 2 , and CH 3 COOH, respectively.
Without calculating the actual freezing points of each of
these solutions, arrange them from lowest to highest
freezing point.
0 *69.A 0.050 maqueous solution of K 3 [Fe(CN) 6 ] has a freez-
ing point of 0.2800°C. Calculate the total concentration
of solute particles in this solution and interpret your
results.
0 *70.A solution is made by dissolving 1.00 gram each of NaCl,
NaBr, and NaI in 100. g of water. What is the vapor pres-
sure above this solution at 100°C? Assume complete
dissociation of the three salts.
*071.The ice fish lives under the polar ice cap where the water
temperature is 4°C. This fish does not freeze at that
temperature due to the solutes in its blood. The solute
concentration of the fish’s blood can be related to a
sodium chloride solution that would have the same freez-
ing point. What is the minimum concentration of a
sodium chloride solution that would not freeze at 4°C?
*072.Which solution freezes at a lower temperature, 0.1 m
sodium sulfate or 0.1 mcalcium sulfate? Explain.
*073.Solutions are produced by dissolving 25.0 grams of
sodium sulfate in 0.500 kg of water and by dissolving
25.0 grams of calcium sulfate in 0.500 kg of water. Which
solution will freeze at a lower temperature? Explain.
*074.A series of 1.1 maqueous solutions is produced. Predict
which solution of each pair would boil at the higher tem-
perature. (a) NaCl or LiCl; (b) LiCl or Li 2 SO 4 ; (c) Li 2 SO 4
or HCl; (d) HCl or C 6 H 12 O 6 ; (e) C 6 H 12 O 6 or CH 3 OH;
(f) CH 3 OH or CH 3 COOH; (g) CH 3 COOH or NaCl.
*075.Identify which of the following solutions, each prepared
by dissolving 65.0 g of the solute in 150. mL of water,
will display the highest boiling point and explain your
choice. (a) NaCl or LiCl; (b) LiCl or Li 2 SO 4 ; (c) Li 2 SO 4
or HCl; (d) HCl or C 6 H 12 O 6 ; (e) C 6 H 12 O 6 or CH 3 OH;
(f) CH 3 OH or CH 3 COOH; (g) CH 3 COOH or NaCl.*076.Synthetic ocean water can be produced by dissolving
36.0 g of table salt in 1000. mL of water. What is the
boiling point of this solution? (Assume that the density
of the water is 0.998 g/mL and that table salt is pure
sodium chloride.)
*077.Formic acid, HCOOH, ionizes slightly in water.HCOOH(aq) 34 H(aq)HCOO(aq)A 0.0100 mformic acid solution freezes at 0.0209°C.
Calculate the percent ionization of HCOOH in this
solution.
*078.A 0.100 m acetic acid solution in water freezes at
0.1884°C. Calculate the percent ionization of
CH 3 COOH in this solution.
0 *79.In a home ice cream freezer, we lower the freezing point
of the water bath surrounding the ice cream can by
dissolving NaCl in water to make a brine solution. A
15.0% brine solution is observed to freeze at 10.888°C.
What is the van’t Hoff factor, i,for this solution?
*080.CsCl dissolves in water according to
H 2 O
CsCl(s)8888nCs(aq)Cl(aq)A 0.121 msolution of CsCl freezes at 0.403°C. Calcu-
late iand the apparent percent dissociation of CsCl in
this solution.Osmotic Pressure
*081.What are osmosis and osmotic pressure?
0 *82.Show numerically that the molality and molarity of 1.00
10 ^4 Maqueous sodium chloride are nearly equal.
Why is this true? Would this be true if another solvent,
say acetonitrile, CH 3 CN, replaced water? Why or why
not? The density of CH 3 CN is 0.786 g/mL at 20.0°C.
*083.Show how the expression MRT,where is osmotic
pressure, is similar to the ideal gas law. Rationalize qual-
itatively why this should be so.
*084.What is the osmotic pressure associated with a 0.0111 M
aqueous solution of a nonvolatile nonelectrolyte solute at
75°C?
*085.The osmotic pressure of an aqueous solution of a non-
volatile nonelectrolyte solute is 1.17 atm at 0.0°C. What
is the molarity of the solution?
*086.Calculate the freezing point depression and boiling point
elevation associated with the solution in Exercise 85.
*087.Estimate the osmotic pressure associated with 24.5 g of
an enzyme of molecular weight 4.21 106 dissolved in- mL of ethyl acetate solution at 38.0°C.
088.Calculate the osmotic pressure at 25°C of 0.10 mK 2 CrO 4
in water, taking ion association into account. Refer to
Table 14-3.
089.Estimate the osmotic pressure at 25°C of 0.10 mK 2 CrO 4
in water, assuming no ion association.