AP Chemistry 1994 Exam

29. When an aqueous solution of NaOH is added to an aqueous solution of potassium dichromate, K2Cr2O7 the dichromate ion is converted to (A) CrO42¯ (B) CrO2 (C) Cr3+ (D) Cr2O3(s) (E) Cr(OH)3(s)

A

48. PCl3(g) + Cl2(g) <===> PCl5(g) + energy Some PCl3 and Cl2 are mixed in a container at 200 °C and the system reaches equilibrium according to the equation above. Which of the following causes an increase in the number of moles of PCl5 present at equilibrium? I. Decreasing the volume of the container II. Raising the temperature III. Adding a mole of He gas at constant volume (A) I only (B) II only (C) I and III only (D) II and III only (E) I, II, and III

A

57. Molecules that have planar configurations include which of the following? I. BCl3 II. CHCl3 III. NCl3 (A) I only (B) III only (C) I and II only (D) II and III only (E) I, II, and III

A

62. The electron-dot structure (Lewis structure) for which of the following molecules would have two unshared pairs of electrons on the central atom? (A) H2S (B) NH3 (C) CH4 (D) HCN (E) CO2

A

65. Barium sulfate is LEAST soluble in a 0.01-molar solution of which of the following? (A) Al2(SO4)3 (B) (NH4)2SO4 (C) Na2SO4 (D) NH3 (E) BaCl2

A

68. Which of the following molecules has a dipole moment of zero? (A) C6H6 (benzene) (B) NO (C) SO2 (D) NH3 (E) H2S

A

70. To determine the molar mass of a solid mono protic acid, a student titrated a weighed sample of the acid with standardized aqueous NaOH. Which of the following could explain why the student obtained a molar mass that was too large? I. Failure to rinse all acid from the weighing paper into the titration vessel II. Addition of more water than was needed to dissolve the acid III. Addition of some base beyond the equivalence point (A) I only (B) III only (C) I and II only (D) II and III only (E) I, II, and III

A

73. 2 SO2(g) + O2(g) <===> 2 SO3(g) When 0.40 mole of SO2 and 0.60 mole of O2 are placed in an evacuated 1.00-liter flask, the reaction represented above occurs. After the reactants and the product reach equilibrium and the initial temperature is restored, the flask is found to contain 0.30 mole of SO3. Based on these results, the equilibrium constant, Kc for the reaction is (A) 20. (B) 10. (C) 6.7 (D) 2.0 (E) 1.2

A

Look at the Phase Diagram for 5-7 (A) Sublimation (B) Condensation (C) Solvation (D) Fusion (E) Freezing 5. If the temperature increases from 10° C to 60° C at a constant pressure of 0.4 atmosphere, which of the processes occurs?

A

Look for Answers 43. Which of the following pairs of compounds are isomers? (A) (B) (C) (D) (E)

A

Questions 11-13 (A) Pb (B) Ca (C) Zn (D) As (E) Na 13. Utilized as a shield from sources of radiation

A

16. Commercial vinegar was titrated with NaOH solution to determine the content of acetic acid, HC2H3O2. For 20.0 milliliters of the vinegar 26.7 milliliters of 0.600-molar NaOH solution was required. What was the concentration of acetic acid in the vinegar if no other acid was present? (A) 1.60 M (B) 0.800 M (C) 0.600 M (D) 0.450 M (E) 0.200 M

B

19. In which of the following compounds is the mass ratio of chromium to oxygen closest to 1.62 to 1.00 ? (A) CrO3 (B) CrO2 (C) CrO (D) Cr2O (E) Cr2O3

B

23. Step 1: Ce4+ + Mn2+ ---> Ce3+ + Mn3+ Step 2: Ce4+ + Mn3+ ---> Ce3+ + Mn4+ Step 3: Mn4+ + Tl+ ---> Tl3+ + Mn2+ The proposed steps for a catalyzed reaction between Ce4+ and Tl+ are represented above. The products of the overall catalyzed reaction are (A) Ce4+ and Tl+ (B) Ce3+ and Tl3+ (C) Ce3+ and Mn3+ (D) Ce3+ and Mn4+ (E) Tl3+ and Mn2+

B

49. The isomerization of cyclopropane to propylene is a first-order process with a half-life of 19 minutes at 500 °C. The time it takes for the partial pressure of cyclopropane to decrease from 1.0 atmosphere to 0.125 atmosphere at 500 °C is closest to (A) 38 minutes (B) 57 minutes (C) 76 minutes (D) 152 minutes (E) 190 minutes

B

Look at the Phase Diagram for 5-7 (A) Sublimation (B) Condensation (C) Solvation (D) Fusion (E) Freezing 6. If the temperature decreases from 110° C to 40° C at a constant pressure of 1.1 atmospheres, which of the processes occurs?

B

36. Zn(s) + Cu2+ ---> Zn2+ + Cu(s) An electrolytic cell based on the reaction represented above was constructed from zinc and copper half-cells. The observed voltage was found to be 1.00 volt instead of the standard cell potential, E°, of 1.10 volts. Which of the following could correctly account for this observation? (A) The copper electrode was larger than the zinc electrode. (B) The Zn2+ electrolyte was Zn(NO3)2, while the Cu2+ electrolyte was CuSO4. (C) The Zn2+ solution was more concentrated than the Cu2+ solution. (D) The solutions in the half-cells had different volumes. (E) The salt bridge contained KCl as the electrolyte.

C

Look at diagram 40. The system shown above is at equilibrium at 28 °C. At this temperature, the vapor pressure of water is 28 millimeters of mercury. The partial pressure of O2(g) in the system is (A) 28 mm Hg (B) 56 mm Hg (C) 133 mm Hg (D) 161 mm Hg (E) 189 mm Hg

C

Questions 1-4 (A) Heisenberg uncertainty principle (B) Pauli exclusion principle (C) Hund's rule (principle of maximum multiplicity) (D) Shielding effect (E) Wave nature of matter 1. Can be used to predict that a gaseous carbon atom in its ground state is paramagnetic

C

17. Relatively slow rates of chemical reaction are associated with which of the following? (A) The presence of a catalyst (B) High temperature (C) High concentration of reactants (D) Strong bonds in reactant molecules (E) Low activation energy

D

20. . . . Ag+ + . . . AsH3(g) + . . . OH¯ ---> . . . Ag(s) + . . . H3AsO3(aq) + . . . H2O When the equation above is balanced with lowest whole-number coefficients, the coefficient for OH¯ is (A) 2 (B) 4 (C) 5 (D) 6 (E) 7

D

21. Correct statements about alpha particles include which of the following? I. They have a mass number of 4 and a charge of +2. II. They are more penetrating than beta particles. III. They are helium nuclei. (A) I only (B) III only (C) I and II (D) I and III (E) II and III

D

Look at Diagram for 30 30. The energy diagram for the reaction X + Y ---> Z is shown above. The addition of a catalyst to this reaction would cause a change in which of the indicated energy differences? (A) I only (B) II only (C) III only (D) I and II only (E) I, II, and III

D

15. In a molecule in which the central atom exhibits sp3d2 hybrid orbitals, the electron pairs are directed toward the corners of (A) a tetrahedron (B) a square-based pyramid (C) a trigonal bipyramid (D) a square (E) an octahedron

E

74. A solution of calcium hypochlorite, a common additive to swimming-pool water, is (A) basic because of the hydrolysis of the OCl¯ ion (B) basic because Ca(OH)2 is a weak and insoluble base (C) neutral if the concentration is kept below 0.1 molar (D) acidic because of the hydrolysis of the Ca2+ ions (E) acidic because the acid HOCl is formed

A

Questions 1-4 (A) Heisenberg uncertainty principle (B) Pauli exclusion principle (C) Hund's rule (principle of maximum multiplicity) (D) Shielding effect (E) Wave nature of matter 4. Predicts that it is impossible to determine simultaneously the exact position and the exact velocity of an electron

A

52. When dilute nitric acid was added to a solution of one of the following chemicals, a gas was evolved, This gas turned a drop of limewater, Ca(OH)2, cloudy, due to the formation of a white precipitate. The chemical was (A) household ammonia, NH3 (B) baking soda, NaHCO3 (C) table salt, NaCl (D) epsom salts, MgSO4 . 7H2O (E) bleach, 5% NaOCl

B

56. It is suggested that SO2 (molar mass 64 grams), which contributes to acid rain, could be removed from a stream of waste gases by bubbling the gases through 0.25-molar KOH, thereby producing K2SO3. What is the maximum mass of SO2 that could be removed by 1,000. liters of the KOH solution? (A) 4.0 kg (B) 8.0 kg (C) 16 kg (D) 20. kg (E) 40. kg

B

58. N2(g) + 3 H2(g) ---> 2 NH3(g) The reaction indicated above is thermodynamically spontaneous at 298 K, but becomes nonspontaneous at higher temperatures. Which of the following is true at 298 K? (A) DG, DH, and DS are all positive. (B) DG, DH, and DS are all negative. (C) DG and DH are negative, but DS is positive. (D) DG and DS are negative, but DH is positive. (E) DG and DH are positive, but DS is negative.

B

60. I2(g) + 3 Cl2(g) ---> 2 ICl3(g) According to the data in the table below, what is the value of DH° for the reaction represented above? Bond Average Bond Energy (kilojoules / mole) I---I 149 Cl---Cl 239 I---Cl 208 (A) - 860 kJ (B) - 382 kJ (C) + 180 kJ (D) + 450 kJ (E) + 1,248 kJ

B

61. A 1-molar solution of which of the following salts has the highest pH ? (A) NaNO3 (B) Na2CO3 (C) NH4Cl (D) NaHSO4 (E) Na2SO4

B

63. What is the maximum mass of copper that could be plated out by electrolyzing aqueous CuCl2 for 16.0 hours at a constant current of 3.00 amperes? (1 faraday = 96,500 coulombs) (A) 28 grams (B) 57 grams (C) 64 grams (D) 114 grams (E) 128 grams

B

75. A direct-current power supply of low voltage (less than 10 volts) has lost the markings that indicate which output terminal is positive and which is negative. A chemist suggests that the power supply terminals be connected to a pair of platinum electrodes that dip into 0.1-molar KI solution. Which of the following correctly identifies the polarities of the power supply terminals? (A) A gas will be evolved only at the positive electrode. (B) A gas will be evolved only at the negative electrode. (C) A brown color will appear in the solution near the negative electrode. (D) A metal will be deposited on the positive electrode. (E) None of the methods above will identify the polarities of the power supply terminals.

B

Look at the Phase Diagram for 5-7 (A) Sublimation (B) Condensation (C) Solvation (D) Fusion (E) Freezing 7. If the pressure increases from 0.5 to 1.5 atmospheres at a constant temperature of 50° C, which of the processes occurs?

B

Questions 1-4 (A) Heisenberg uncertainty principle (B) Pauli exclusion principle (C) Hund's rule (principle of maximum multiplicity) (D) Shielding effect (E) Wave nature of matter 3. Indicates that an atomic orbital can hold no more than two electrons

B

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 (B) Vapor pressure (C) Freezing point (D) Electrical conductivity (E) Absorption of visible light

C

24. A sample of 0.0100 mole of oxygen gas is confined at 37° C and 0.216 atmosphere. What would be the pressure of this sample at 15° C and the same volume? (A) 0.0876 atm (B) 0.175 atm (C) 0.201 atm (D) 0.233 atm (E) 0.533 atm

C

26. Which of the following actions would be likely to change the boiling point of a sample of a pure liquid in an open container? I. Placing it in a smaller container II. Increasing the number of moles of the liquid in the container III. Moving the container and liquid to a higher altitude (A) I only (B) II only (C) III only (D) II and III only (E) I, II, and III

C

27. Which of the following sets of quantum numbers (n, l, ml, ms) best describes the valence electron of highest energy in a ground-state gallium atom (atomic number 31) ? (A) 4, 0, 0, 1/2 (B) 4, 0, 1, 1/2 (C) 4, 1, 1, 1/2 (D) 4, 1, 2, 1/2 (E) 4, 2, 0, 1/2

C

31. H2C2O4 + 2 H2O ---> 2 H3O+ + C2O42¯ Oxalic acid, H2C2O4, is a diprotic acid with K1 = 5.36 x 10¯2 and K2 = 5.3 x 10¯5. For reaction above, what is the equilibrium constant? (A) 5.36 x 10¯2 (B) 5.3 x 10¯5 (C) 2.8 x 10¯6 (D) 1.9 x 10¯10 (E) 1.9 x 10¯13

C

33. A hydrocarbon gas with an empirical formula CH2 has a density of 1.88 grams per liter at 0 °C and 1.00 atmosphere. A possible formula for the hydrocarbon is (A) CH2 (B) C2H4 (C) C3H6 (D) C4H8 (E) C5H10

C

38. Concentrations of colored substances are commonly measured by means of a spectrophotometer. Which of the following would ensure that correct values are obtained for the measured absorbance? I. There must be enough sample in the tube to cover the entire light path. II. The instrument must be periodically reset using a standard. III. The solution must be saturated. (A) I only (B) II only (C) I and II only (D) II and III only (E) I, II, and III

C

39. Samples of F2 gas and Xe gas are mixed in a container of fixed volume. The initial partial pressure of the F2 gas is 8.0 atmospheres and that of the Xe gas is 1.7 atmospheres. When all of the Xe gas reacted, forming a solid compound, the pressure of the unreacted F2 gas was 4.6 atmospheres. The temperature remained constant. What is the formula of the compound? (A) XeF (B) XeF3 (C) XeF4 (D) XeF6 (E) XeF8

C

45. A sample of an ideal gas is cooled from 50.0 °C to 25.0 °C in a sealed container of constant volume. Which of the following values for the gas will decrease? I. The average molecular mass of the gas II. The average distance between the molecules III. The average speed of the molecules (A) I only (B) II only (C) III only (D) I and III (E) II and III

C

55. What volume of 0.150-molar HCl is required to neutralize 25.0 millilters of 0.120-molar Ba(OH)2? (A) 20.0 mL (B) 30 0 mL (C) 40.0 mL (D) 60.0 mL (E) 80.0 mL

C

69. Correct procedures for a titration include which of the following? I. Draining a pipet by touching the tip to the side of the container used for the titration II. Rinsing the buret with distilled water just before filling it with the liquid to be titrated III. Swirling the solution frequently during the titration (A) I only (B) II only (C) I and III only (D) II and III only (E) I, II, and III

C

71 ... Fe(OH)2 + ... O2 + ... H2O ---> ... Fe(OH)3 If 1 mole of O2 oxidizes Fe(OH)2 according to the reaction represented above, how many moles of Fe(OH)3 can be formed? (A) 2 (B) 3 (C) 4 (D) 5 (E) 6

C

8-10 Refer to the following diatomic species (A) Li2 (B) B2 (C) N2 (D) O2 (E) F2 10. Contains 1 sigma (s) and 2 pi (p) bonds

C

8-10 Refer to the following diatomic species (A) Li2 (B) B2 (C) N2 (D) O2 (E) F2 8. Has the largest bond-dissociation energy

C

Questions 11-13 (A) Pb (B) Ca (C) Zn (D) As (E) Na 11. Utilized as a coating to protect Fe from corrosion

C

25. H2(g) + (1/2) O2(g) ---> H2O(l) DH° = - 286 kJ 2 Na(s) + (1/2) O2(g) ---> Na2O(s) DH° = - 414 kJ Na(s) + (1/2) O2(g) + (1/2) H2(g) ---> NaOH(s) DH° = - 425 kJ Based on the information above, what is the standard enthalpy change for the following reaction? Na2O(s) + H2O(l) ---> 2 NaOH(s) (A) -1,125 kJ (B) -978 kJ (C) -722 kJ (D) -150 kJ (E) +275 kJ

D

32. CH3CH2OH boils at 78 °C and CH3OCH3 boils at - 24 °C, although both compounds have the same composition. This difference in boiling points may be attributed to a difference in (A) molecular mass (B) density (C) specific heat (D) hydrogen bonding (E) heat of combustion

D

35. For which of the following processes would DS have a negative value? I. 2 Fe2O3(s) ---> 4 Fe(s) + 3 O2(g) II. Mg2+ + 2 OH¯ ---> Mg(OH)2(s) III. H2(g) + C2H4(g) ---> 3 C2H6(g) (A) I only (B) I and II only (C) I and III only (D) II and III only (E) I, II, and III

D

37. A sample of 3.30 grams of an ideal gas at 150.0 °C and 1.25 atmospheres pressure has a volume of 2.00 liters. What is the molar mass of the gas? The gas constant, R, is 0.0821 L atm mol¯1 K¯1). (A) 0.0218 gram/mole (B) 16.2 grams/mole (C) 37.0 grams/mole (D) 45.8 grams/mole (E) 71.6 grams/mole

D

41. A strip of metallic scandium, Sc, is placed in a beaker containing concentrated nitric acid. A brown gas rapidly forms, the scandium disappears, and the resulting liquid is brown-yellow but becomes colorless when warmed. These observations best support which of the following statements? (A) Nitric acid is a strong acid. (B) In solution scandium nitrate is yellow and scandium chloride is color less. (C) Nitric acid reacts with metals to form hydrogen. (D) Scandium reacts with nitric acid to form a brown gas. (E) Scandium and nitric acid react in mole propor tions of 1 to 3.

D

42. Mass of an empty container = 3.0 grams Mass of the container plus the solid sample = 25.0 grams Volume of the solid sample = 11.0 cubic centimeters The data above were gathered in order to determine the density of an unknown solid. The density of the sample should be reported as (A) 0.5 g/cm3 (B) 0.50 g/cm3 (C) 2.0 g/cm3 (D) 2.00 g/cm3 (E) 2.27 g/cm3

D

47. Which of the following has the lowest conductivity? (A) 0.1 M CuS04 (B) 0.1 M KOH (C) 0.1 M BaCl2 (D) 0.1 M HF (E) 0.1 M HNO3

D

51. 4 HCl(g) + O2(g) <===> 2 Cl2(g) + 2 H2O(g) Equal numbers of moles of HCl and O2 in a closed system are allowed to reach equilibrium as represented by the equation above. Which of the following must be true at equilibrium? I. [HCl] must be less than [Cl2]. II. [O2] must be greater than [HCl]. III. [Cl2] must equal [H2O]. (A) I only (B) II only (C) I and III only (D) II and III only (E) I, II, and III

D

54. All of the following statements concerning the characteristics of the halogens are true EXCEPT: (A) The first ionization energies (potentials) decrease as the atomic numbers of the halogens increase. (B) Fluorine is the best oxidizing agent. (C) Fluorine atoms have the smallest radii. (D) Iodine liberates free bromine from a solution of bromide ion. (E) Fluorine is the most electronegative of the halogens.

D

59. When a 1.00-gram sample of limestone was dissolved in acid, 0.38 gram of CO2 was generated. If the rock contained no carbonate other than CaCO3, what was the percent of CaCO3 by mass in the limestone? (A) 17% (B) 51% (C) 64% (D) 86% (E) 100%

D

64. At 25 °C, a sample of NH3 (molar mass 17 grams) effuses at the rate of 0.050 mole per minute. Under the same conditions, which of the following gases effuses at approximately one-half that rate? (A) O2 (molar mass 32 grams) (B) He2 (molar mass 4.0 grams) (C) CO2 (molar mass 44 grams) (D) Cl2 (molar mass 71 grams) (E) CH4 (molar mass 16 grams)

D

66. What is the pH of a 1.0 x 10¯2-molar solution of HCN? (For HCN, Ka = 4.0 x 10¯10.) (A) 10 (B) Between 7 and 10 (C) 7 (D) Between 4 and 7 (E) 4

D

8-10 Refer to the following diatomic species (A) Li2 (B) B2 (C) N2 (D) O2 (E) F2 9. Has a bond order of 2

D

Questions 11-13 (A) Pb (B) Ca (C) Zn (D) As (E) Na 12. Is added to silicon to enhance its properties as a semiconductor

D

18. 2 H2O + 4 MnO4¯ + 3 ClO2¯ ---> 4 MnO2 + 3 ClO4¯ + 4 OH¯ Which species acts as an oxidizing agent in the reaction represented above? (A) H2O (B) ClO4¯ (C) ClO2¯ (D) MnO2 (E) MnO4¯

E

22. HSO4¯ + H2O <===> H3O+ + SO42¯ In the equilibrium represented above, the species that act as bases include which of the following? I. HSO4¯ II. H2O III. SO42¯ (A) II only (B) III only (C) I and II (D) I and III (E) II and III

E

28. Given that a solution is 5 percent sucrose by mass, what additional information is necessary to calculate the molarity of the solution? I. The density of water II. The density of the solution III. The molar mass of sucrose (A) I only (B) II only (C) III only (D) I and III (E) II and III

E

34. X = CH3-CH2-CH2-CH2-CH3 Y = CH3-CH2-CH2-CH2-OH Z = HO-CH2-CH2-CH2-OH Based on concepts of polarity and hydrogen bonding, which of the following sequences correctly lists the compounds above in the order of their increasing solubility in water? (A) Z < Y < X (B) Y < Z < X (C) Y < X < Z (D) X < Z < Y (E) X < Y < Z

E

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

E

46. Which of the following solids dissolves in water to form a colorless solution? (A) CrCl3 (B) FeCl3 (C) CoCl2 (D) CuCl2 (E) ZnCl2

E

50. Which of the following acids can be oxidized to form a stronger acid? (A) H3PO4 (B) HNO3 (C) H2CO3 (D) H3BO3 (E) H2SO3

E

53. If 87 grams of K2 SO4 (molar mass 174 grams) is dissolved in enough water to make 250 milliliters of solution, what are the concentrations of the potassium and the sulfate ions? [K+] [SO42¯] (A) 0.020 M 0.020 M (B) 1.0 M 2.0 M (C) 2.0 M 1.0 M (D) 2.0 M 2.0 M (E) 4.0 M 2.0 M

E

67. Substances X and Y that were in a solution were separated in the laboratory using the technique of fractional crystallization. This fractional crystallization is possible because substances X and Y have different (A) boiling points (B) melting points (C) densities (D) crystal colors (E) solubilities

E

72. The nuclide 245Cm is radioactive and decays by the loss of one beta ([beta]¯) particle. The product nuclide is (A) 245Pu (B) 95Am (C) 248Cm (D) 250Cm (E) 97Bk

E

Questions 1-4 (A) Heisenberg uncertainty principle (B) Pauli exclusion principle (C) Hund's rule (principle of maximum multiplicity) (D) Shielding effect (E) Wave nature of matter 2. Explains the experimental phenomenon of electron diffraction

E