Olympic High School  AP Chemistry
Name _________________________________
Period ___ Date ___/___/___
14  Solutions and Their Behavior
STUDY
QUESTIONS
1.
35.0 g of a salt (molar mass 90 g mol-1) were dissolved to make 100 g of solution which has a density
of 1.29 g/mL.
Calculate the molarity of the solution.
2.
Concentrated sulfuric acid contains very little water, only 5.0% by mass. It has a density of 1.84
g/mL. What is the molarity of this acid?
3.
The lattice energy of a salt is 350 kJ/mol and the solvation energies of its ions add up to 320 kJ/mol
for the preparation of a 0.50 M solution. In the preparation of this solution would the solution get
colder or warmer? What is the driving force for this solution process?
4.
Addition of excess sodium nitrate to water to form a saturated solution results in the following
equilibrium. The solution process is endothermic. NaNO3(s)
Na+(aq) + NO3(aq)
How could the concentration of sodium nitrate in the solution be increased? Explain.
a. add more NaNO3(s)
b. increase the pressure on the solution
c. increase the temperature
d. stir the solution more vigorously
5.
The value of Henry’s law constant kH for oxygen in water at 24C is 1.66 x 10-6 M/torr.
a. Calculate the solubility of oxygen in water at 25C when the total external pressure is 1 atm and
the mole fraction of oxygen in the air is 0.20.
b. Calculate the solubility at the same temperature with the same atmospheric composition but at an
increased pressure of 2 atm.
c. What would happen to the solubility of the oxygen gas if the temperature was increased?
6.
Ethanol (CH3OH) and methanol (C2H5OH) form an almost ideal solution. If 64 g of methanol is
mixed with 69 g of ethanol, what is the total vapor pressure above the solution?
The vapor pressure of pure methanol at this temperature = 90 torr.
The vapor pressure of pure ethanol at this temperature = 45 torr.
(hint: there are two volatile substances in this solution)
7. Cigars are best stored in a “humidor” at 18°C and 55% relative humidity. This means the pressure of water
vapor should be 55% of the vapor pressure of pure water at the same temperature. The proper humidity
can be maintained by placing a solution of glycerol [C3H5(OH)3] and water in the humidor. Calculate the
percentage by mass of glycerol that will lower the vapor pressure of water to the desired value. (Assume
the vapor pressure of glycerol is negligible.)
8. A solution is made by adding 50.0 mL of ethanol (C2H5OH) to 50.0 mL of water. What is the total vapor
pressure over the solution at 20°C? The vapor pressure of ethanol at 20°C is 43.6 mm Hg and its density
is 0.785 g/mL. The vapor pressure of water is 17.5°C at the same temperature.
9. Which of the following substances is likely to dissolve in water, and which is likely to dissolve in benzene
(C6H6)?
(a) NaNO3
(b) Diethyl ether, CH3CH2OCH2CH3
(c) Naphthalene (C10H8)
(d) NH4Cl
(e) I2
10. Some lithium chloride, LiCl, is dissolved in 100 mL of water in one beaker and some Li2SO4 is dissolved
in 100 mL of water in another beaker. Both are at 10°C and both are saturated solutions; some solid
remains undissolved in each beaker. Describe what you would observe as the temperature is raised giving
reasons for your answers. The following data are available to you from the handbook of chemistry:
11. When salts of Mg2+, Na+, and Cs+ are placed in water, the positive ion is hydrated (as is the negative ion).
Which of these three cations is most strongly hydrated? Why?
Which one is least strongly hydrated? Why?
12. Henry’s law constant for O2 in water at 25°C is 1.66 × 10−6 M/mm Hg. Which of the following is a
reasonable constant when the temperature is 50°C? Explain the reason for your choice.
(a) 8.8 × 10−7 M/mm Hg
(b) 3.40 × 10−6 M/mm Hg
(c) 1.66 × 10−6 M/mm Hg
(d) 8.40 × 10−5 M/mm Hg