U.S. National Chemistry Olympiad: 1985 Local Section Test

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1. Which measurement contains three significant figures?

(A) 2.00 cm³
(B) 0.20 cm³
(C) 0.02 cm³
(D) 0.002 cm³

2. An analytical balance is capable of measuring mass to the nearest 0.1 mg. Which measurement correctly reflects the precision which can be obtained when using this balance?

(A) 2.06 g
(B) 2.060 g
(C) 2.0600 g
(D) 2.06000 g

3. A sample of gallium has an atomic weight of approximately 69.8. If the sample consists of two isotopes of masses 69.0 and 71.0 respectively, what is the approximate percentage of the lighter isotope in the sample?

(A) 80.0 %
(B) 60.0 %
(C) 40.0 %
(D) 20.0 %

4. One basic assumption in the Bohr theory of the structure of the hydrogen atom was that

(A) the electron could have any of a continuous range of energies.
(B) the electron could exist in any one of a set of discrete energy levels.
(C) the electron could move from a higher to a lower energy orbit by absorbing a quantum of energy.
(D) electromagnetic radiation would be given off as the electron moved in orbit around the nucleus.

5. Which experiment led to the belief that the atom contained an extremely small, positively charged nucleus?

(A) Millikan's oil drop experiment
(B) Rutherford's scattering experiment
(C) Thomson's cathode ray tube experiment
(D) Moseley's experiment on X-ray emission by metals

6. According to the Heisenberg Uncertainty Principle, as the wavelength of light used to locate an electron decreases,

(A) the error in determining its position increases and the error in determining its momentum increases also.
(B) the error in determining its position decreases and the error in determining its momentum decreases also.
(C) the error in determining its position increases and the error in determining its momentum decreases.
(D) the error in determining its position decreases and the error in determining its momentum increases.

7. Relative atomic and molar masses are determined with a mass spectrometer utilizing the fact that

(A) the velocity of the paritcles can be accurately determined.
(B) a definite fraction of the particles is formed in a charged state.
(C) all particles with the same charge to mass ratio follow the same curved path.
(D) the force with which the accelerated particles strike a target can be measured.

8. If a neutral atom has an atomic number of 29 and a mass number of 61, then the atom must contain

(A) 90 neutrons
(B) 61 electrons
(C) 29 neutrons
(D) 29 electrons

9. Atom X has 9 protons, 9 electrons, and 10 neutrons. Atom Y has 10 protons, 10 electrons, and 9 neutrons. It can therefore be concluded that

(A) atom X and Y are isotopes.
(B) atom X is more massive than atom Y.
(C) atoms X and Y have the same mass number.
(D) atoms X and Y have the same atomic number.

10. Which set of quantum numbers (n, l, m, s) represents the outermost electron in a gaseous aluminum atom?

(A) 2, 1, 0, +1/2
(B) 2, 1, -1, +1/2
(C) 3, 0, 0, +1/2
(D) 3, 1, -1, +1/2

11. What is the energy of a photon with a wavelength of 6400 nm?

(A) 4.2 x 10¯⁴⁰ J
(B) 4.2 x 10¯³¹ J
(C) 3.1 x 10¯¹⁹ J
(D) 3.1 x 10¯¹⁷ J

12. The attraction that nonpolar molecules have for each other is primarily caused by the presence of

(A) gravity.
(B) hydrogen bonding.
(C) van der Waals' forces.
(D) permanent dipole-dipole interactions.

13. The geometries of the molecules BF₃ and NF₃ are trigonal planar and trigonal pyramidal respectively. Which statement best accounts for the difference?

(A) N is more elctronegative than B.
(B) BF₃ is ionic, which NF₃is covalent.
(C) B utilizes sp hybridization, while N does not.
(D) N has a non-bonding pair of valence electrons, while B does not.

14. The best example of a nonpolar molecule containing polar bonds is

(A) F₂
(B) SO₂
(C) CS₂
(D) PCl₃

15. Which molecule utilizes sp³ hybridization according to Valence Bond Theory?

(A) NH₃
(B) BF₃
(C) BeF₂
(D) XeF₄

16. How many oxygen molecules are contained in a 3.25 L flask at 25.0 °C and a pressure of 725 torr (mm of Hg)? Assume ideal behavior.

(A) 7.63 x 10¹⁹
(B) 7.63 x 10²²
(C) 9.90 x 10²³
(D) 5.80 x 10²⁵

17. Which statement best explains why real gases sometimes exhibit a measured volume greater than that which is calculated from the Ideal Equation of State?

(A) Molecules have a finite size.
(B) Collisions between molecules are not elastic.
(C) Significant intermolecular attractions exist between molecules.
(D) High temperatures result in a significant decrease in pressures.

18. A gas which will diffuse twice as fast as SO₂ (MW = 64) is

(A) He (MW = 4)
(B) CH₄ (MW = 16)
(C) O₂ (MW = 32)
(D) HI (MW = 128)

19. An ideal gas occupies a volume of 31.6 Liters at a pressure of 735 torr (mm of Hg) and a temperature of 25.0 °C. Which expression correctly calculates the volume of the gas at a pressure of 765 torr (mm of Hg) and a temperature of 50.0 °C?

(A) (31.6 L) (735/765) (323/298)
(B) (31.6 L) (735/765) (298/323)
(C) (31.6 L) (765/735) (298/323)
(D) (31.6 L) (765/735) (323/298)

20. The density of an unknown gas at 65.0 °C and a pressure of 730 torr (mm of Hg) is 2.14 g L¯¹. The density of oxygen gas at the same conditions is 1.11 g L¯¹. What is the molar mass of the unknown gas?

(A) 16.6 g mol¯¹
(B) 47.9 g mol¯¹
(C) 61.7 g mol¯¹
(D) 76.0 g mol¯¹

21. A white solid has these properties:

1. The solid is soluble in water.
2. The solid is soluble in chloroform, CHCl₃.
3. The pure solid does not conduct electricity.
4. An aqueous solution of the solid conducts electricity.
5. When the solid is melted, the resulting liquid does not conduct electricity.

Based upon this information, this solid would most likely be classified as

(A) ionic.
(B) metallic.
(C) polar covalent.
(D) covalent network.

22. Which substance should have the highest boiling temperature?

(A) CH₄
(B) C₂H₆
(C) C₃H₈
(D) C₄H

23. Ethyl alcohol, C₂H₅OH, has a molar heat of fusion of 4.81 kJ mol¯¹. Calculate DH when 8.72 grams of ethyl alcohol freezes.

(A) +0.912 kJ
(B) -0.912 kJ
(C) +41.9 kJ
(D) -41.9 kJ

24. Water can exist at 100.0 °C and 1.00 atm pressure as

(A) only a gas
(B) only a liquid
(C) a liquid and a gas
(D) a liquid and a solid

25. How many grams of NaBr could be formed if 14.2 grams of NaI were reacted with reacted with 40.0 mL of 0.800 M Br₂?

2 NaI + Br₂ ---> 2 NaBr + I₂

(A) 3.30
(B) 4.80
(C) 6.59
(D) 9.75

26. Under proper conditions, ammonia, NH₃, and oxygen, O₂, react to form nitrogen and water. How many moles of oxygen would be consumed for each mole of nitrogen formed?

(A) 0.67
(B) 0.75
(C) 1.5
(D) 3.0

27. The equation for the complete combustion of methanol is

2 CH₃OH(l) + 3 O₂(g) ---> 2 CO₂(g) + 4 H₂O(g)

If 64 grams of methanol is combined with 44.8 liters of oxygen, measured at STP, the number of moles of carbon dioxide which can be produced is

(A) 2/3
(B) 1 1/3
(C) 1 1/2
(D) 4

28. A compound is analyzed and found to consist of 50.4% Ce, 15.1% N, and 34.5% O by mass. What is the correct empirical (simplest) formula for the compound?

(A) Ce₂(NO₃)₂
(B) Ce₂(NO₂)₃
(C) Ce(NO₃)₂
(D) Ce(NO₂)₃

29. What is the molarity of the sulfate ion in a solution prepared by dissolving 17.1 grams of aluminum sulfate, Al₂(SO₄)₃, in enough water to prepare 1.00 L of solution. Neglect any hydrolysis.

(A) 1.67 x 10¯² M
(B) 5.00 x 10¯² M
(C) 1.50 x 10¯¹ M
(D) 2.50 x 10¯¹ M

30. In a titration, 15.0 cm³ of 0.100 M hydrocholric acid neutralizes 30.0 cm³ of a solution of calcium hydroxide. What is the molarity of the calcium hydroxide solution?

(A) 0.0125
(B) 0.0250
(C) 0.0500
(D) 0.200

31. The net ionic equation for the precipitation reaction that occurs when aqueous solutions of AgNO₃ and K₂CrO₄ are mixed is

(A) K⁺ + NO₃¯ ---> KNO₃(s)
(B) Ag⁺ + CrO₄¯ ---> AgCrO₄(s)
(C) K₂⁺ + NO₃¯ ---> K₂NO₃(s)
(D) 2Ag⁺ + CrO₄²¯ ---> Ag₂CrO₄(s)

32. Which salt produces an acidic solution when dissolved in water?

(A) NaC₂H₃O₂
(B) Li₃PO₄
(C) AlCl₃
(D) KNO₃

33. In the reaction

2 HCO₃¯ <===> H₂CO₃ + CO₃²¯

the hydrogen carbonate ion, HCO₃¯ is functioning as

(A) a Bronsted-Lowry acid only.
(B) a Bronsted-Lowry base only.
(C) both a Bronsted-Lowry acid and a Bronsted-Lowry base.
(D) neither a Bronsted-Lowry acid nor a Bronsted-Lowry base.

34. Which pair of species consists of a Lewis acid followed by a Lewis base?

(A) Cl¯(aq), Ag⁺(aq)
(B) NH₃(g), BF₃(g)
(C) SO₄²¯(aq), HSO₄¯(aq)
(D) H⁺(aq), OH¯(aq)

35. A reaction for which DH < 0 and DS < 0 is most likely to have which of these thermodynamic properties?

(A) The reaction cannot be spontaneous at any temperature.
(B) The reaction will tend to be spontaneous at low temperatures.
(C) The reaction will tend to be spontaneous at high temperatures.
(D) The spontaneity of the reaction will be independent of temperature.

36. For the reaction X(g) + Y(g) ---> Z(g) this kinetic data was obtained

Calculate the initial rate of the reaction in Exp. #4.

(A) 4.36 x 10¯³
(B) 5.81 x 10¯³
(C) 7.27 x 10¯³
(D) 9.69 x 10¯³

37. Below is a potential energy graph for a simple one-step reaction, A ---> B.

What is the value of the activation energy for the reaction B ---> A?

(A) -30 kJ
(B) +20 kJ
(C) +30 kJ
(D) +50 kJ

38. A small increase in temperature often produces a large increases in the rate of a chemical reaction because it

(A) decreases the activation energy of the reaction.
(B) increases the effectiveness of the collisions between the reactant molecules.
(C) decreases the number of collisions per second between the reactant molecules.
(D) decreases the volume of the solution, altering the concentrations of the reactants.

39. Calculate the pH of a solution made by mixing 150 cm³ of 0.10 M NaC₂H₃O₂ and 250 cm³ of 0.10 M HC₂H₃O₂. K_a of HC₂H₃O₂ = 1.8 x 10¯⁵

(A) 2.37
(B) 4.52
(C) 4.74
(D) 4.97

40. Consider the equilibrium reaction

4 NH₃(g) + 3 O₂(g) <===> 2 N₂(g) + 6 H₂O(g)

DH = -1268 kJ

Which change will cause the reaction to shift to the right?

(A) Increase the temperature
(B) Decrease the volume of the container.
(C) Add a catalyst to speed up the reaction.
(D) Remove the gaseous water by allowing it to react and be absorbed by KOH.

41. The solubility product constant, K_sp, of Ag₃PO₄ is 1.8 x10¯¹⁸. What is the molar solubility of Ag₃PO₄ in water? Neglect any hydrolysis.

(A) 1.6 x 10¯⁵
(B) 8.4 x10¯⁷
(C) 1.3 x 10¯⁹
(D) 4.5 x 10¯¹⁹

42. The reaction

2 A(g) + B(g) <===> 3 C(g) + D(g)

is begun with the concentrations of A and B both at an initial value of 1.00 M. When equilibrium is reached, the concentration of D is measured and found to be 0.25 M. The value for the equilibrium constant for this reaction is given by the expression

(A) [(0.75)³ (0.25)] ÷ [(0.50)² (0.75)]
(B) [(0.75)³ (0.25)] ÷ [(0.50)² (0.25)]
(C) [(0.75)³ (0.25)] ÷ [(0.75)² (0.25)]
(D) [(0.75)³ (0.25)] ÷ [(1.00)² (1.00)]

43. The chemical reaction taking place in a dry cell may be written

Zn(s) + 2 H⁺(aq) + 2 MnO₂(s) ---> Zn²⁺(aq) + 2 MnO(OH).

The battery is to be discarded after 2.00 g of zinc is converted to Zn²⁺(aq). If 0.0100 amperes of current is continuously drawn, for how many seconds can the battery operate?

(A) [(65.4) (0.0100)] ÷ [(2) (96,500)]
(B) [(2) (96,500)] ÷ [(0.0100) (65.4)]
(C) [(2) (65.4) (96,500)] ÷ (0.0100)
(D) [(2.00) (2) (96,500)] ÷ [(65.4) (0.0100)]

44. In the oxidation-reduction reaction

Sn⁴⁺ + 2 Fe²⁺ ---> 2 Fe³⁺ + Sn²⁺

(A) Sn⁴⁺ is the oxidizing agent and Fe²⁺ is the reducing agent.
(B) Sn⁴⁺ is the reducing agent and Fe²⁺ is the oxidizing agent.
(C) Sn⁴⁺ is the reducing agent and Fe³⁺ is the oxidizing agent.
(D) Fe³⁺ is the oxidizing agent and Sn²⁺ is the reducing agent.

45. Given the standard reduction potentials

Calculate the standard voltage for the reaction

2 Al(s) + 3 Cu²⁺ ---> 2 Al³⁺ + 3 Cu(s)

(A) -1.22 Volt
(B) +2.00 Volt
(C) +4.34 Volt
(D) +5.86 Volt

46. The half-life of ²¹⁴Bi is 19.7 min. Starting with 1.00 x 10¯³ grams of ²¹⁴Bi, how many grams remain after 59.1 min?

(A) 1.25 x 10¯⁴
(B) 2.50 x 10¯⁴
(C) 3.33 x 10¯⁴
(D) 5.00 x 10¯⁴

47. Consider the unbalanced equation

__ Fe²⁺ + __ MnO₄¯ + __ H⁺ ---> __ Mn²⁺ + __ Fe³⁺ + __ H₂O

When properly balanced with the simplest set of whole number coefficients, the sum of the coefficients in the balanced equation is

(A) 12
(B) 18
(C) 22
(D) 24

48. An isotope of uranium undergoes a fission reaction when bombarded with neutrons.

What is the mass number of the uranium isotope used?

(A) 233
(B) 235
(C) 237
(C) 238

49. Which acid can be considered to be an organic acid?

(A) nitric
(B) sulfuric
(C) carbonic
(D) acetic

50. An amber-colored, crystalline element burns in air with blue flame, producing an irritating gas. The gas turns moist litmus paper red. The element exists in more than one amorphous form, one of which is a caramel-colored gummy substance. The element is

(A) sulfur
(B) carbon
(C) silicon
(D) phosphorus

51. A white compound is produced by precipitating it from an aqueous solution. There is a possibility that the compound may be contaminated by Cu²⁺. To test for the contamination, the compound is subsequently dissolved in aqueous ammonia. If Cu²⁺ were present in the precipitate, the solution produced would be expected to exhibit what color?

(A) blue
(B) green
(C) orange
(D) yellow

52. Compounds which exhibit color are

(A) Cr₂O₃ and Fe(OH)₃
(B) NaNO₃ and KCl
(C) Mg(NO₃)₂ and BaCl₂
(D) AlCl₃ and Zn(NO₃)₂

53. Which series is ranked in order of increasing electronegativity?

(A) O, S, Se, Te
(B) Cl, S, P, Si
(C) In, Sn, N, O
(D) C, Si, P, Se

54. Atom T has 3 valence electrons and atom S has 6 valence electrons. The formula expected for an ionic compound of T and S is

(A) T₂S₃
(B) T₃S₂
(C) TS₃
(D) T₂S

55. Which gaseous atom has the highest 2nd ionization energy?

(A) C
(B) Li
(C) F
(D) Ne

56. A 5.00 gram sample of BaCl₂ contaminated with an inert substance is dissolved in 200 mL of water and reacted with an excess of AgNO₃ solution, precipitating AgCl. If 3.23 grams of AgCl are precipitated, what was the percentage by mass of BaCl₂ in the original sample?

(A) 38.9
(B) 46.9
(C) 64.6
(D) 93.0

57. A student heats 3.000 g of crystalline CuSO₄ ^. 5H₂O until it is converted into anhydrous CuSO₄. She reports the anhydrous compound to have a measured mass of 2.000 g. What is the student's approximate percent error in the mass of the anhydrous compound, assuming the molar masses of the hydrate and the anhydrous compound to be 249.7 mol¯¹ and 159.6 g mol¯¹ respectively?

(A) +3.3
(B) +4.3
(C) +6.7
(D) +8.5

58. When performing an acid-base titration, which procedure would NOT introduce an error into the experimental results

(A) adding an unmeasured amount of water to the carefully measured acid sample which is being titrated.
(B) failing to rinse the burettes with the appropriate reactants after cleaning and rinsing with water.
(C) failing to remove bubbles of air from the tips of the burettes before beginning the titration.
(D) using an indicator that changes color at a pH considerably removed from the pH at the equivalence point of the titration.

59. For the reaction

2 C₂H₅OH(l) + 6 O₂(l) ---> 4 CO₂(g) + 6 H₂O(l)

for which DH° = -2733.6 kJ, calculate the standard enthalpy (heat) of formation of C²H⁵OH(l), in kJ mol¯¹, given that the standard enthalpies of formation of CO₂(g) and H₂O(l) are -393.1 and -285.5 kJ mol-1 respectively.

(A) -275.9
(B) -551.8
(C) +1027.5
(D) +2055.0

60. Which represents a valid method for dissolving a precipitate of silver chloride?

(A) add silver nitrate solution
AgCl(s) + Ag⁺(aq) + NO₃¯(aq) ---> 2Ag⁺(aq) + Cl¯(aq) + NO₃¯(aq)

(B) Add sodium hydroxide
AgCl(s) + Na⁺(aq) + OH¯(aq) ---> NaCl(aq) + Ag⁺(aq) + OH¯(aq)

(C) Add hydrochloric acid
AgCl(s) + H⁺(aq) + Cl¯(aq) ---> Ag⁺(aq) + Cl₂(g) + H⁺(aq)

(D) Add aqueous ammonia
AgCl(s) + 2NH₃(aq) ---> Ag(NH₃)²⁺(aq) + Cl¯(aq)

61. Which species is paramagnetic in the gaseous state?

(A) Cu⁺
(B) Zn²⁺
(C) Sn²⁺
(D) Cr³⁺

62. Which kind(s) of isomerism may be exhibited by the molecule

(A) optical only
(B) geometrical only
(C) both geometrical and optical
(D) neither geometrical nor optical

63. An ionic solid has a unit cell consisting of A ions at the corners of a cube and B ions on the centers of the faces of the cube. The empirical formula for this solid would be

(A) AB
(B) A₂B
(C) AB₃
(D) A₃B

64. 1.05 kg of frozen organic solvent (already at its normal freezing temperature) is place in 10.0 kg of water, originally at 50.0 °C. The enthalpy of fusion of the organic solvent is 127 kJ kg¯¹. The specific heat of water is 4.18 J g¯¹ °C¯¹. The water temperature when the organic solvent has just finished melting is approximately

(A) 50 °C
(B) 47 °C
(C) 24 °C
(D) 0 °C

65. A 0.100 m aqueous solution of a weak electroyte, HY, freezes at -0.214 °C. What is the approximate percent ionization of HY? The freezing poing depression constant for water is 1.86 °C / m.

(A) 3.98
(B) 11.5
(C) 15.0
(D) 21.4

66. If a substance has a molar heat of vaporization of 3.05 x 10⁴ J mol¯¹ and a normal boiling temperature of 80.0 °C, what is the value of its molar entropy of vaporization, DS_vap, in J K¯¹ mol¯¹?

(A) 0.0116
(B) 86.4
(C) 381
(D) 1.08 x 10⁷

67. The Gibbs Free Energy change at 25.0 °C for the reaction

Ag⁺(aq) + I¯(aq) ---> AgI(s)

is -91.9 kJ mol¯¹. The equilibrium constant for the reaction as written is

(A) 7.78 x 10¯¹⁷
(B) 1.29 x 10¹⁶
(C) 1.24 x 10³⁷
(D) 37.1

68. The reaction

A + B ---> AB

is 1st order with respect to A and zero order with respect to B. The reaction is begun with the initial concentration of both reactants at 0.100 M. After 1.5 hours the concentration of B has dropped to 0.060 M. What is the approximate value of the specific rate (reaction rate) constant for this reaction?

(A) 0.15 hr¯¹
(B) 0.34 hr¯¹
(C) 0.61 hr¯¹
(D) the specific rate constant cannot be determined unless the mechanism of the reaction known.

69. 25.0 cm³ of a 0.050 M solution of formic acid, HCOOH, was neutralized with 25.0 cm³ of a 0.050 M solution of sodium hydroxide, NaOH. What is the pH of the resulting solution? K_a for HCOOH = 2.1 x 10¯⁴

(A) 5.96
(B) 6.61
(C) 7.39
(D) 8.04

70. The standard reduction potentials for Al³⁺ and Zn²⁺ are -1.66 Volt and -0.76 Volt respectively. Calculate the free energy change for this reaction as balanced.

2 Al(s) + 3 Zn²⁺(aq) ---> 2 Al³⁺(aq) + Zn(s)

(A) -5.2 x 10⁵ J
(B) -6.0 x 10⁵ J
(C) +9.0 x 10⁵ J
(D) +1.4 x 10⁶ J