Ch 14 Practice: Solutions
AP Chemistry 2011-12
AP Multiple Choice Questions. 1989
27.
I. Difference in temperature between freezing point of solvent and freezing point of solution
II. Molal freezing point depression constant, Kf, for solvent
In addition to the information above, which of the following gives the minimum data required to determine the
molecular mass of a nonionic substance by the freezing point depression technique?
(A) No further information is necessary.
(B) Mass of solute
(C) Mass of solute and mass of solvent
(D) Mass of solute and volume of solvent
(E) Mass of solute, mass of solvent, and vapor pressure of solvent
71. A solution of toluene (molecular weight 92.1) in benzene (molecular weight 78.1) is prepared. The mole
fraction of toluene in the solution is 0.100. What is the molality of the solution?
(A) 0.100 m
(D) 1.28 m
(B) 0.703 m
(E) 1.42 m
(C) 0.921 m
1994
14. Which of the following is lower for a 1.0-molar aqueous solution of any solute than it is for pure water?
(A) pH
(D) Electrical conductivity
(B) Vapor pressure
(E) Absorption of visible light
(C) Freezing point
28. Given that a solution is 5 percent sucrose by mass, what additional information is necessary to calculate the
molarity of the solution?
1. The density of water
II. The density of the solution
Ill. The molar mass of sucrose
(A) I only
(D) I and III
(B) II only
(E) II and III
(C) III only
44. Which of the following solutions has the lowest freezing point?
(A) 0.20 m C6H12O6, glucose
(B) 0.20 m NH4Br
(C) 0.20 m ZnSO4
(D) 0.20 m KMnO4
(E) 0.20 m MgCl2
1999
31. If the temperature of an aqueous solution of NaCl is increased from 20°C to 90°C, which of the following
statements is true?
(A) The density of the solution remains unchanged.
(B) The molarity of the solution remains unchanged.
(C) The molality of the solution remains unchanged.
(D) The mole fraction of solute decreases.
(E) The mole fraction of solute increases.
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43. A sample of 61.8 g of H3BO3, a weak acid, is dissolved in 1,000 g of water to make a 1.0-molal solution.
Which of the following would be the best procedure to determine the molarity of the solution? (Assume no
additional information is available.)
(A) Titration of the solution with standard acid
(B) Measurement of the pH with a pH meter
(C) Determination of the boiling point of the solution
(D) Measurement of the total volume of the solution
(E) Measurement of the specific heat of the solution
52. Under which of the following sets of conditions could the most O2(g) be dissolved in H2O(l) ?
Pressure of O2(g)
Above H2O(l)
(atm)
(A) 5.0
(B) 5.0
(C) 1.0
(D) 1.0
(E) 0.5
Temperature
of H2O(l)
(°C)
80
20
80
20
20
73. The volume of distilled water that should be added to 10.0 mL of 6.00 M HCl(aq) in order to prepare a
0.500 M HCl(aq) solution is approximately
(A) 50.0 mL
(D) 110. mL
(B) 60.0 mL
(E) 120. mL
(C) 100. mL
75. Which of the following pairs of liquids forms the solution that is most ideal (most closely follows Raoult's
law)?
(A) C8H18(l) and H2O(l)
(B) CH3CH2CH2OH(l)and H2O(l)
(C) CH3CH2CH2OH(l) and C8H18(l)
(D) C6H14(l) and C8Hl8(l)
(E) H2SO4(l) and H2O(l)
2002
26. Approximately what mass of CuSO4 ⋅ 5H2O (250 g mol-l) is required to prepare 250 mL of 0.10 M
copper(II) sulfate solution?
(A) 4.0 g
(B) 6.2 g
(C) 34 g
(D) 85 g
(E) 140 g
35. A solution is made by dissolving a nonvolatile solute in a pure solvent. Compared to the pure solvent, the
solution
(A) has a higher normal boiling point
(D) has a higher freezing point
(B) has a higher vapor pressure
(E) is more nearly ideal
(C) has the same vapor pressure
38. A 0.10 M aqueous solution of sodium sulfate, Na2SO4, is a better conductor of electricity than a 0.10 M
aqueous solution of sodium chloride, NaCl. Which of the following best explains this observation?
(A) Na2SO4 is more soluble in water than NaCl is.
(B) Na2SO4has a higher molar mass than NaCl has.
(C) To prepare a given volume of 0.10 M solution, the mass of Na2SO4 needed is more than twice the mass
of NaCl needed.
(D) More moles of ions are present in a given volume of 0.10 M Na2SO4 than in the same volume of 0.10 M
NaCl.
(E) The degree of dissociation of Na2SO4 in solution is significantly greater than that of NaCl.
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39. On the basis of the solubility curves shown above, the greatest
percentage of which compound can be recovered by cooling a
saturated solution of that compound from 90°C to 30°C?
(A) NaCl
(B) KNO3
(C) K2CrO4
(D) K2SO4
(E) Ce2(SO4)3
45. What is the mole fraction of ethanol, C2H5OH, in an aqueous
solution that is 46 percent ethanol by mass? (The molar mass of C2H5OH is 46 g; the molar mass of H2O is
18 g.)
(A) 0.25
(D) 0.67
(B) 0.46
(E) 0.75
(C) 0.54
69. If 200. mL of 0.60 M MgCl2(aq) is added to 400. mL of distilled water, what is the concentration of
Mg2+(aq) in the resulting solution? (Assume volumes are additive.)
(A) 0.20 M
(D) 0.60 M
(B) 0.30 M
(E) 1.2 M
(C) 0.40 M
AP Free Response Questions
1996 B
Concentrated sulfuric acid (18.4-molar H2SO4) has a density of 1.84 grams per milliliter. After dilution with
water to 5.20-molar, the solution has a density of 1.38 grams per milliliter and can be used as an electrolyte in
lead storage batteries for automobiles.
(a) Calculate the volume of concentrated acid required to prepare 1.00 liter of 5.20-molar H2SO4.
(b) Determine the mass percent of H2SO4 in the original concentrated solution.
(c) Calculate the volume of 5.20-molar H2SO4 that can be completely neutralized with 10.5 grams of sodium
bicarbonate, NaHCO3.
(d) What is the molality of the 5.20-molar H2SO4?
1998 B
An unknown compound contains only the three elements C, H, and O. A pure sample of the compound is
analyzed and found to be 65.60 percent C and 9.44 percent H by mass.
(a) Determine the empirical formula of the compound.
(b) A solution of 1.570 grams of the compound in 16.08 grams of camphor is observed to freeze at a
temperature 15.2 Celsius degrees below the normal freezing point of pure camphor. Determine the molar
mass and apparent molecular formula of the compound. (The molal freezing-point depression constant, Kâ,
for camphor is 40.0 kg•K•mol-1.)
(c) When 1.570 grams of the compound is vaporized at 300°C and 1.00 atmosphere, the gas occupies a volume
of 577 milliliters. What is the molar mass of the compound based on this result?
(d) Briefly describe what occurs in solution that accounts for the difference between the results obtained in
parts (b) and (c).
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1999 D
Answer the following questions, which refer to the 100 mL samples of
aqueous solutions at 25ºC in the stoppered flasks shown above.
(a) Which solution has the lowest electrical conductivity? Explain.
(b) Which solution has the lowest freezing point? Explain.
(c) Above which solution is the pressure of the water vapor greatest?
Explain.
(d) Which solution has the highest pH? Explain.
2000
5. The molar mass of an unknown solid, which is nonvolatile and a nonelectrolyte, is to be determined by the
freezing-point depression method. The pure solvent used in the experiment freezes at 10ºC and has a known
molal freezing-point depression constant, Kf . Assume that the following materials are also available.
test tubes
stirrer
pipet
thermometer
balance
beaker
stopwatch
graph paper
hot-water bath ice
(a) Using the two sets of axes provided below, sketch cooling curves for (i) the pure solvent and for (ii) the
solution as each is cooled from 20ºC to 0.0ºC.
(b) Information from these graphs may be used to determine the molar mass of the unknown solid.
(i) Describe the measurements that must be made to determine the molar mass of the unknown solid
by this method.
(ii) Show the setup(s) for the calculation(s) that must be performed to determine the molar mass of the
unknown solid from the experimental data.
(iii) Explain how the difference(s) between the two graphs in part (a) can be used to obtain information
needed to calculate the molar mass of the unknown solid.
(c) Suppose that during the experiment a significant but unknown amount of solvent evaporates from the
test tube. What effect would this have on the calculated value of the molar mass of the solid (i.e., too
large, too small, or no effect)? Justify your answer.
(d) Show the setup for the calculation of the percentage error in a student's result if the student obtains a
value of 126 g mol-1 for the molar mass of the solid when the actual value is 120. g mol-1.
2003 Question 4
For each of the following, use appropriate chemical principles to explain the observations. Include
chemical equations as appropriate.
(a) In areas affected by acid rain, statues and structures made of limestone (calcium carbonate) often
show signs of considerable deterioration.
(b) When table salt (NaCl) and sugar (C12H22O11) are dissolved in water, it is observed that
(i) both solution have higher boiling points than pure water, and
(ii) the boiling point of 0.10 M NaCl(aq) is higher than that of 0.10 M C12H22O11(aq).
(c) Methane gas does not behave as an ideal gas at low temperatures and high pressures.
(d) Water droplets form on the outside of a beaker containing an ice bath.
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