Princeton 2012/Barron 4th ed.

AP Practice ProblemsUnit 9 Solutions

Multiple Choice (no calculator)For questions 1-3, one or more of the following responses will apply; each response may be used more than once or not at all in these questions.A. Molarity (M)

B. Molality (m)

C. Density

D. pH

E. pOH

1. Has the units moles/kg. (P9.1)

2. Can have the units grams/liter. (P9.3)

3. Has the units moles per liter (P9.4)

4. Which of the following is (are) colligative properties? (P9.5)

I. Freezing-point depressionII. Vapor pressure lowering

III. Boiling-point elevation

a. I only

b. I and II only

c. I and III only

d. II and III only

e. I, II, and III

5. Which of the following aqueous solutions has the highest boiling point? (P9.6)

a. 0.5m NaCl

b. 0.5m KBr

c. 0.5m CaCl2d. 0.5m C6H12O6e. 0.5m NaNO36. When sodium chloride is added to a saturated solution of silver chloride, which of the following precipitates would be expected to appear? (P9.7)

a. Sodium

b. Silver

c. Chlorine

d. Sodium chloride

e. Silver chloride

7. A substance is dissolved in water, forming a 0.50-molar solution. If 4.0 liters of solution contains 240 grams of the substance, what is the molecular mass of the substance? (P9.8)a. 60 grams/mole

b. 120 grams/mole

c. 240 grams/mole

d. 480 grams/mole

e. 640 grams/mole

8. When 31.0 grams of a nonionic substance is dissolved in 2.00 kg of water, the observed freezing-point depression of the solution is 0.93C. If kf for water is 1.86C/m, which of the following expressions is equal to the molar mass of the substance? (P9.11)a. g/molb. g/molc. g/mold. g/mole. (31.0)(0.93)(1.86)(2.00) g/mol9. What is the boiling point of a 2 m solution of NaCl in water? (The boiling point elevation constant, kb, for water is 0.5C/m.) (P9.12)

a. 100C

b. 101C

c. 102C

d. 103C

e. 104C

10. When an aqueous solution of potassium chloride is compared with water, the salt solution will have (P9.13)

a. a higher boiling point, a lower freezing point, and a lower vapor pressure

b. a higher boiling point, a higher freezing point, and a lower vapor pressure

c. a higher boiling point, a higher freezing point, and a higher vapor pressure

d. a lower boiling point, a lower freezing point, and a lower vapor pressure

e. a lower boiling point, a higher freezing point, and a higher vapor pressure

11. If 46 grams of MgBr2 (molar mass 184 grams) are dissolved in water to form 0.50 liters of solution, what is the concentration of bromine ions in the solution? (P9.14)

a. 0.25-molar

b. 0.50-molar

c. 1.0-molar

d. 2.0-molar

e. 4.0-molar

12. A solution contains equal masses of glucose (molecular mass 180) and toluene (molecular mass 90). What is the mole fraction of glucose in the solution? (P9.15)

a.

b. 1/3

c.

d. 2/3

e.

13. When benzene and toluene are mixed together, they form an ideal solution. If benzene has a higher vapor pressure than toluene, then the vapor pressure of a solution that contains an equal number of moles of benzene and toluene will be (P9.16)

a. higher than the vapor pressure of benzeneb. equal to the vapor pressure of benzene

c. lower than the vapor pressure of benzene and higher than the vapor pressure of toluene

d. equal to the vapor pressure of toluene

e. lower than the vapor pressure of toluene

14. How many moles of Na2SO4 must be added to 500 milliliters of water to create a solution that has a 2-molar concentration of the Na+ ion? (Assume the volume of the solution does not change). (P9.17)

a. 0.5 moles

b. 1 mole

c. 2 moles

d. 4 moles

e. 5 moles

15. Given that a solution of NaCl (molar mass 58.5 g/mole) in water (molar mass 18 g/mole) has a molality of 0.5m, which of the following can be determined? (P9.18)

I. The mass of the NaCl in the solution

II. The total mass of the solution

III. The mole fraction of the NaCl in the solution

a. I only

b. III only

c. I and II only

d. II and III only

e. I, II, and III

16. How many liters of water must be added to 4 liters of a 6-molar HNO3 solution to create a solution that is 2-molar? (P9.19)a. 2 liters

b. 4 liters

c. 6 liters

d. 8 liters

e. 12 liters

17. Which of the following expressions is equal to the Ksp of Ag2CO3? (P9.20)a. Ksp = [Ag+][CO3-2]

b. Ksp = [Ag+][CO3-2]2c. Ksp = [Ag+]2[CO3-2]

d. Ksp = [Ag+]2 [CO3-2] 2e. Ksp = [Ag+]2 [CO3-2] 318. If the solubility of BaF2 is equal to x, which of the following expressions is equal to the solubility product, Ksp, for BaF2? (P9.21)

a. x2b. 2x2c. x3d. 2x3e. 4x319. A beaker contains 50.0 mL of a 0.20 M Na2SO4 solution. If 50.0 mL of a 0.10 M solution of Ba(NO3)2 is added to the beaker, what will be the final concentration of sulfate ions in the solution? (P9.22)a. 0.20 M

b. 0.10 M

c. 0.050 M

d. 0.025 M

e. 0.012 M

20. The bottler of a carbonated beverage dissolves carbon dioxide in water by placing carbon dioxide in contact with water at a pressure of 1 atm at room temperature. The best way to increase the amount of dissolved CO2 would be to (P9.24)

a. increase the temperature and increase the pressure of CO2b. decrease the temperature and decrease the pressure of CO2c. decrease the temperature and increase the pressure of CO2d. increase the temperature without changing the pressure of CO2e. increase the pressure of CO2 without changing the temperature

21. Copper II chloride will be LEAST soluble in a 0.02-molar solution of which of the following compounds? (P9.27)

a. NaCl

b. CuNO3c. CaCl2d. NaCO3e. KI

For questions 22-25, one or more of the following responses will apply. Each response may be used more than once or not at all in these questions.

I. Osmotic PressureII. Freezing-point Depression

III. Vapor Pressure

IV. Raoults Law

V. Henrys Law

22. Which of these best explains why a soda bottle fizzes when opened? (B9.1)a. I

b. II

c. III

d. IV

e. V

23. Which of these is the method of choice to determine the molecular mass of large biomolecules? (B9.2)a. I

b. II

c. III

d. IV

e. V

24. Which two items are most closely related to each other? (B9.3)a. I and IIIb. II and V

c. III and IV

d. IV and V

e. V and I

25. The extent of ion pairing in a solution of an electrolyte can be best estimated by using which of these? (B9.4)a. I and III

b. II

c. III and V

d. IV

e. V

26. All of the following physical properties change as solute is added to the solution. Which is NOT a colligative property? (B9.7)a. Boiling point

b. Surface tension

c. Vapor pressure

d. Melting point

e. Osmotic pressure

27. Which of the following is expected to be the most soluble in hexane, C6H14? (B9.8)a. KCl

b. C2H5OH

c. C6H6d. H2O

e. HC2H3O228. Molarity units are most appropriate in calculating which of the following? (B9.9)a. Freezing-point depression

b. Vapor pressure

c. Boiling-point elevation

d. Surface tension

e. Osmotic pressure

29. All of the following may be used to determine molar masses. Which one requires an ideal solution for accurate results? (B9.10)a. Freezing-point depression

b. Boiling-point elevation

c. Osmotic pressure

d. Vapor pressure

e. Gas density

30. To make a solution, 3.45 mol of C6H13Cl and 1.26 mol of C5H12 are mixed. Which of the following is needed, but not readily available, to calculate the molarity of this solution? (B9.11)a. The density of the solution

b. The densities of C6H13Cl and C5H12c. The temperature

d. The molar masses of C6H13Cl and C5H12e. The volumes of C6H13Cl and C5H1231. Ethyl alcohol, C2H5OH, and water become noticeable warmer when mixed. This is due to (B9.13)a. The decrease in volume when they are mixed

b. Smaller attractive forces in the mixture than in the pure liquids

c. The hydrogen bonding of the two liquids

d. The change in vapor pressure observed

e. Stronger attractive forces in the mixture than in the pure liquids

32. Which is the most appropriate method for determining the molar mass of a newly discovered enzyme? (B9.14)a. Freezing-point depression

b. Osmotic pressure

c. Boiling-point depression

d. Gas density

e. Vapor pressure

33. When algae decay in a pond, the process uses up the available oxygen. Which of the following factors will also contribute to a decrease in oxygen in a pond? (B9.16)a. Decreasing salinity (salt concentration)

b. Increasing acidity due to acid rain

c. Increasing temperature

d. Increasing surface tension of the water

e. Increasing atmospheric pressure

34. Which of the following compounds is incorrectly classified? (B9.19)a. NaF electrolyte

b. CH3OH weak electrolyte

c. Mg(C2H3O2)2 electrolyte

d. CH3CH2COOH weak electrolyte

e. Glucose nonelectrolyte 35. If equal numbers of moles of each of the following are dissolved in 1 kg of distilled water, the one with the lowest boiling point will be (B9.21)a. NaF

b. AlCl3c. Mg(C2H3O2)2d. CH3CH2COOH

e. Glucose

36. Which of the following changes as temperature changes? (B6.2)

a. Molarity

b. Mass percentage

c. Molar mass

d. Empirical formula

e. Molecular formula

Additional Multiple Choice Calculator my be used37. The solubility of cadmium chloride, CdCl2 is 140 g per 100 mL of solution. What is the molar solubility (molarity) of a saturated solution of CdCl2? (B9.5)

a. 0.765 M

b. 1.31 M

c. 7.65 M

d. 12.61 M

e. 0.131 M

38. The vapor pressure of an ideal solution is 456 mmHg. If the vapor pressure of the pure solvent is 832 mmHg, what is the mole fraction of the nonvolatile solute? (B9.6)

f. 0.548

g. 0.345

h. 0.645

i. 1.82

j. 0.452

39. Which of the following, when added to 1.00 kg H2O, is expected to give the greatest increase in the boiling point of water? (kb = 0.052Cm-1) (B9.12)

k. 1.25 mol sucrose

l. 0.25 mol iron (III) nitrate

m. 0.50 mol ammonium chloride

n. 0.60 mol calcium sulfate

o. 1.00 mol acetic acid

40. A polluted pond contains 25 ppb of lead ions. What is the concentration of lead ions in molarity units? (B9.15)

a. 1.2108 M

b. 1.210-7 M

c. 2.510-8 M

d. 0.121 M

e. 1.210-10 M

41. Liquid A has a vapor pressure of 437 mmHg, and liquid B has a vapor pressure of 0.880 atm at 85C. Which of the following represents a possible solution of the two liquids? (B9.17)

a. A mixture with a vapor pressure of 345 mmHg

b. A mixture with a vapor pressure of 0.750 atm

c. A mixture with a boiling point of 165C

d. A mixture with a vapor pressure of 1106 mmHg

e. A mixture with a boiling point of 85C

42. The freezing-point depression constant for water is 1.86Cm-1. When 100 g of a compound is dissolved in 500 g H2O, the freezing point is -10C. Of the five possibilities below, which is the identity of the compound? (B9.18)

a. Mg(NO3)2b. KCl

c. Na2SO4d. HCOOH

e. HF

43. The kf and kb values for water are 1.86 and 0.52Cm-1, respectively. A solution boils at 107.5C. At what temperature does this solution freeze? (B9.20)

a. 7.5C

b. -7.5C

c. 0.0C

d. -26.8C

e. -284.5C

44. The solubility of acetylene, CHCH, in water at 30C is 0.975gL-1 when the pressure of acetylene is 1.00 atm. What is the solubility, at the same temperature, when the pressure of acetylene above the water is reduced to 0.212 atm? (B9.22)

a. 4.60 gL-1b. 0.207 gL-1c. 0.975 gL-1d. 0.212 gL-1e. The answer cannot be determined from the data

45. If 20.0g of ethanol (molar mass = 46) and 30.0g of water (molar mass = 18) are mixed together, the mole fraction of ethanol in this mixture is (B9.24)

a. 0.207

b. 0.261

c. 0.739

d. 0.793

e. 4.83

46. What weight of KClO3 (molar mass = 122.5) is needed to make 200 mL of a 0.150 M solution of this salt? (B6.5)

a. 2.73 g

b. 3.68 g

c. 27.3 g

d. 164 g

e. 3.69 g

47. How many milligrams of Na2SO4 (molar mass = 142) are needed to prepare 100 mL of a solution that is 0.00100 M in Na+ ions? (B6.10)

a. 28.4

b. 14,200

c. 1.00

d. 7.1

e. 14.2

Essays1. The molecular weight and formula of a hydrocarbon are to be determined through the use of the freezing-point depression method. The hydrocarbon is known to be 86 percent carbon and 14 percent hydrogen by mass. In the experiment, 3.72 grams of the unknown hydrocarbon were placed into 50.0 grams of liquid benzene, C6H6. The freezing point of the solution was measured to be 0.06C. The normal freezing point of benzene is 5.50C, and the freezing-point depression constant for benzene is 5.12C/m. (P9.1)a. What is the molecular weight of the compound?

b. What is the molecular formula of the hydrocarbon?

c. What is the mole fraction of benzene in the solution?

d. If the density of the solution is 875 grams per liter, what is the molarity of the solution?2. Explain the following statements in terms of the chemical properties of the substances involved. (P9.3)a. A 1-molal aqueous solution of sodium chloride has a lower freezing point than a 1-molal aqueous solution of ethanol.

b. NaCl is a strong electrolyte, whereas PbCl2 is a weak electrolyte.

c. Propanol is soluble in water, but propane is not.

d. In a dilute aqueous solution, molarity and molality have the same value.

3. Answer the following questions according to the equation below. (P5.4)

2 Mg(s) + 2 CuSO4(aq) + H2O(l) ( 2 MgSO4(aq) + Cu2O(s) + H2(g)

a. If 1.46 grams of Mg(s) are added to 500mL of a 0.200 M solution of CuSO4, what is the maximum molar yield of H2(g)?

b. When all of the limiting reagent has been consumed in (a), how many moles of the other reactant (not water) remain?

c. What is the mass of the Cu2O produced in (a)?

d. What is the value of [Mg+2] in the solution at the end of the experiment? (Assume that the volume of the solution remains unchanged.)

4. Consider solutions and their behaviors. (B9.1)

a. Explain the concept like dissolves like.

b. Explain how a nonvolatile, non-dissociating solute affects the boiling point of a solvent.

c. The freezing-point depression constant of cyclohexane is 20.2C per molal. The melting point of cyclohexane is 6.50C. What is the freezing point of a hexane solution prepared by dissolving 20.0 g of C18H38 in 100 g of cyclohexane?

d. Solutes in aqueous systems are usually classified based on how electricity is conducted. Name these classifications and give an example of each.

e. A solution is prepared by dissolving 15.2 milligrams of CrCl3 in 2.50 liters of water. What is the concentration of cesium in parts per million?

Answer Key Unit 9 Solutions

Multiple Choice1. B2. C

3. A

4. E

5. C

6. E

7. B

8. B

9. C

10. A

11. C

12. B

13. C

14. A

15. B

16. D

17. C

18. E

19. C

20. C

21. C

22. E

23. A

24. C

25. B

26. B

27. C

28. E

29. D

30. A

31. E

32. B

33. C

34. B

35. E

36. AAdditional Multiple Choice

37. C

38. E

39. A

40. B

41. B

42. B

43. D

44. B

45. A

46. B

47. D

Essays

1. For the problema. Freezing point depression T = 5.50C 0.06C = 5.44C

T = kfm5.44C = (5.12C/m)mm = 1.06

m = moles solute/kg solvent

Rearrange to

moles solute = (molality)(kg solvent)

moles solute = (1.06m)(0.050 kg) = 0.053 moles

Molecular weight = grams/mole = 3.72 g/0.053 moles = 70.2 grams

b. Use percent by mass and molecular weightFor carbon ( (86%)(70g/mol) = 60 g/mol

Molar mass of carbon = 12 g/mol so 60/12 = 5 moles C

For hydrogen ( (14%)(70g/mol) = 10 g/mol

Molar mass of hydrogen = 1 g/mol so 10/1 = 10 moles H

Molecular Formula = C5H10c. There are 0.053 moles of hydrocarbon. Find moles of benzene.

Total moles = 0.64 mol + 0.53 mol = 0.69 mol

Mole fraction = 0.64/0.69 = 0.93d. M = mol/L

Mass of solution = 50.00 g + 3.72 g = 53.72 g

D = m/V 875 g/L = (53.72g)/(V)

V = 0.0614 L

M = (0.053 mol)/(0.0614 L) = 0.863 M2. For the problema. Freezing-point depression is a colligative property which means that it depends on the number of particles in solution, not their identity. Sodium chloride dissociates into Na+ and Cl- so every unit of sodium chloride produces 2 particles in solution. Ethanol does not dissociate, so sodium chloride will put twice as many particles in solution as ethanol.

b. An electrolyte ionizes in solution causing the solution to conduct electricity. Both salts dissociate into ions, but PbCl2 is almost insoluble, so it will produce very few ions in solution, which NaCl is extremely soluble and produces many ions.

c. Water is best at dissolving polar solvents according to like dissolves like. Propanol (C3H7OH) has a hydroxide group, which makes it polar, and thus soluble in water. Propane (C3H8) is nonpolar and is best dissolved in nonpolar solvents.

d. Molarity = moles solute/liter of solutionMolality = moles of solute/kilograms of solvent

For water, 1 liter weighs 1 kilogram, so for a dilute solution, this distinction disappears. If there is very little solute, the mass and volume of the solution will be indistinguishable from the mass and volume of the solvent.

3. For the problema. M

X = 0.100 mol CuSO4Mg and CuSO4 react in a 1:1 ratio so Mg is the limiting reagent

= 0.030 moles H2b. Moles of CuSO4 remaining = 0.100 mol 0.060 mol = 0.040 molc. = 0.030 moles Cu2O d. All of the Mg consumed ends up a Mg+2 ions in the solution.

4. Behaviors of solutions

a. Polar substances tend to dissolve polar solutes better than nonpolar solutes and nonpolar solutes dissolve nonpolar solutes better than polar solutes. b. The nonvolatile solute decreases the fraction of the solute with enough kinetic energy to vaporize. Because the vapor pressure is decreased, it therefore requires a higher temperature to achieve a vapor pressure of 1.0 atm than is required for boiling.

c. m = = Tf = -(0.787m)(20.2Cm-1) = -15.91CT = 6.50 15.91 = -9.41Cd. Strong electrolytes completely dissociate in water and conduct electricity well. Weak electrolytes dissociate but not completely. They conduct electricity, but poorly. Nonelectrolytes do not dissociate and do not conduct electricity.e. 15.210-3 g CrCl3