The Chemistry Page: Chemistry Olympiad 1992 Local Section Test

U.S. National Chemistry Olympiad: 1992 Local Section Test

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1. Which represents the ₂₃₅U atom?

Protons Electrons Neutrons

(A) 46 46 143

(B) 92 92 92

(C) 92 92 143

(D) 92 92 146

2. One mole of an element contains 4.82 x 10²⁴ electrons. What is the atomic number of the element?

(A) 2
(B) 4
(C) 6
(D) 8

3. How many H atoms are contained in 1.50 g of glucose (C₆H₁₂O₆)?

(A) 3.01 x 10²²
(B) 1.20 x 10²³
(C) 2.40 x 10²³
(D) 6.02 x 10²²

4. Which contains the greatest mass of chlorine?

(A) 5.0 g Cl₂
(B) 30.0 g MgCl₂
(C) 0.50 mol Cl₂
(D) 0.90 mol KCl

5. A particular chlorofluorocarbon (CFC) contains 9.93% C, 31.43% F, and 58.64% Cl by mass. Its molar mass is 120.9 g/mol. How many F atoms are in one molecule?

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

6. On heating, Cl₂O₇ decomposes to form Cl₂ and O₂. What is the ratio of chlorine to oxygen molecules in the product?

(A) 2 to 7
(B) 2 to 14
(C) 3 to 7
(D) 4 to 7

7. What is the coefficient for Fe²⁺ when the redox equation is

Fe²⁺ + MnO₄Ż + H⁺ ---> Fe³⁺ + Mn²⁺ + H₂O

is balanced when using the smallest whole-number coefficients?

(A) 2
(B) 3
(C) 4
(D) 5

8. Hydrogen peroxide, H₂O₂, in the presence of a catalyst decomposes into water and oxygen gas. How many mL of O₂ at STP are produced from the decomposition of 5.0 g of H₂O₂?

(A) 230 mL
(B) 460 mL
(C) 870 mL
(D) 1650 mL

9. Which statement pertains to the measured pressure of gas collected when O₂ is collected over water?

(A) It is greater than the pressure of dry O₂
(B) It is less than the pressure of dry O₂
(C) It is equal to the pressure of dry O₂
(D) It varies inversely with the pressure of dry O₂

10. Which observation is an exception to the behavior predicted by kinetic molecular theory?

(A) When propane gas is subjected to a high enough pressure, it liquifies.
(B) When an inflated balloon is placed in liquid nitrogen, it flattens, but regains its shape when returned to room temperature.
(C) Tire pressure readings are higher when tires are hot after a long trip.
(D) When the button on a spray can is pushed, the material inside flows out of the can.

11. A gas has a density of 4.36 g LŻ¹ at 20 °C and a pressure of 1.25 atm. Which noble gas best fits these data?

(A) Ne
(B) Ar
(C) Kr
(D) Xe

12. A gas is likely to behave in a non-ideal fashion in all of the situations given except

(A) At very low temperatures, because the particles have insufficient kinetic energy to overcome intermolecular attractions.
(B) in mixtures of gases where the molecules are polar, because intermolecular forces are more likely.
(C) at standard temperature and pressure, because intermolecular interations are minimized.
(D) at very high pressures, because the distance between molecules is likely to be small in relation to molecular diameter.

13. A sample of gas originally occupies 2.56 L at a temperature of 25 °C and a pressure of 686 mmHg. The temperature is increased to 35 °C and the pressure is reduced to 461 mmHg. What is the final volume of gas?

(A) 3.94 L
(B) 3.69 L
(C) 1.78 L
(D) 1.66 L

14. Brass is an alloy composed of

(A) copper and tin.
(B) copper and zinc.
(C) copper and lead.
(D) zinc and tin.

15. When Na₂O₂ dissolves with water, what are the end products?

(A) NaOH(aq) and H₂(g)
(B) NaOH(aq) and O₂(g)
(C) NaH(s) and O₂(g)
(D) Na₂O(s) and O₂(g)

16. The properties of the elements are periodic functions of their

(A) atomic number.
(B) atomic volume
(C) atomic mass
(D) atomic density.

17. The compounds of what element found in fossil fuels are major contributors to acid rain?

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

18. Which list of elements are arranged in order of increasing atomic size (largest last)?

(A) Li, Na , K, Rb
(B) Rb, K Na, Li
(C) Li, Na, Rb, K
(D) Li, K, Na, Rb

19. What is the ground state electronic configuration for the Cu atom?

(A) 1s² 2s² 2p² 3s² 3p⁶ 3d⁹ 4s²
(B) 1s² 2s² 2p⁶ 3s² 3p² 3p⁶ 3d¹⁰ 4s¹
(C) 1s² 2s² 2p⁶ 3s² 3p⁶ 3d⁸ 4s³
(D) 1s² 2s² 2p⁶ 3s² 3p⁶ 3d⁹ 4s¹ 4p¹

20. Which atom has two unpaired electrons and is therefore paramagnetic?

(A) He
(B) Be
(C) B
(D) C

21. What is the ground state electron configuration for the Ba²⁺ ion?

(A) [Xe] 6s¹
(B) [Xe] 6s²
(C) [Xe]
(D) [Kr] 4d¹⁰ 5s² 5p⁴

22. Which sequence is arranged in order of increasing ionization energies?

(A) Be, B, C, N, O
(B) B, Be, C, O, N
(C) Be, B, C,O, N
(D) B, Be, C, N, O

23. When solid iodine sublimes, what are the chemical forces that must be overcome?

(A) intramolecular covalent bonds
(B) hydrogen bonds
(C) dispersion forces
(D) dipole forces

24. Carbon and silicon are in the same chemical family. Which is true for both elements?

(A) Each shows a strong ability to bond to itself in compounds.
(B) Both commonly form multiple bonds by overlap of p atomic orbitals.
(C) In pure form, both often form tetrahedron shaped structures.
(D) All of the above.

25. Which type solid, as a class, generally has a low melting point?

(A) molecular solid
(B) ionic solid
(C) hydrogen bonded solid
(D) metallic solid

26. For which molecule are resonance structures necessary to describe the bonding satisfactorily?

(A) H₂S
(B) SO₂
(C) CO₂
(D) OF₂

27. Which color for flame tests is not correct?

(A) Sodium, yellow
(B) Potassium, violet
(C) lithium, green
(D) all are correct

28. What is the shape and polarity of the PF₃ molecule?

(A) trigonal pyramidal, polar
(B) trigonal pyramidal, nonpolar
(C) trigonal planar, polar
(D) trigonal planar, nonplolar

29. When 50.0 mL of 0.200 M HCl is mixed with 150.0 mL of 0.100 M NaOH, the reaction is as shown.

NaOH(aq) + HCl(aq) ---> NaCl(aq) + H₂O(l)

What is the concentration of the resulting solution?

(A) 0.0500 M NaCl
(B) 0.100 M NaCl
(C) 0.0500 M NaCl and 0.0250 M NaOH
(D) 0.0500 M NaCl and 0.0500 M NaOH

30. Refer to the heating curve to the right for 50.0 g of a compound with a molar mass of 94.1 g. What is the melting point of the compound?

(A) 25
(B) 55
(C) 75
(D) 95

31. Which would you expect to be the strongest acid?

(A) HBrO₃
(B) HIO₃
(C) HClO₃
(D) all should be equally strong.

32. The solubility of which salt is not pH dependent?

(A) CaF₂
(B) CaCO₃
(C) CaC₂O₄
(D) CaCl₂

33. Consider a reaction 2 A(s) + B(g) <===> 2 C(g). If 0.20 mol A, 0.30 mol B and 0.10 mol C are present in a 1. 0 L flask at equilibrium, what is K_c?

(A) 0.033
(B) 0.83
(C) 1.67
(D) 30.3

34. Which effect will not increase the amount of CO(g) present at equilibrium? The reaction is endothermic.

CO₂(g) + H₂(g) <===> CO(g) + H₂O(g)

(A) Decrease the concentration of H₂O(g).
(B) Increase the concentration of H₂(g).
(C) Increase the volume of the container.
(D) Increase the temperature of the container.

35. Which 0.500 M solution has the lowest pH?

(A) HC₂H₃O₂ (K_a = 1.8 x 10Ż⁵)

(B) NaCN (K_b = 2.5 x 10Ż⁵)

(C) NH₃ (K_b = 1.8 x 10Ż⁵)

(D) HN₃ (K_a = 2.0 x 10Ż⁵)

36. 0.2 M hypochlorous acid (pK_a = 7.51) is titrated with 0.2 M sodium hydroxide solution. Which indicator of those with ranges listed would be most appropriate for marking the endpoint of this titration?

(A) methyl orange pH = 3.2-4.4

(B) bromocresol purple pH = 5.2-6.8

(C) cresol red pH = 7.0-8.8

(D) alizarin yellow pH = 10.1-12.0

37. Which oxide is the most acidic?

(A) MgO
(B) CO₂
(C) SO₂
(D) SO₃

38. Which set of quantum numbers represents a 2p electron?

n l m s

(A) 1 0 0 1/2

(B) 2 1 1 1/2

(C) 2 2 -1 -1/2

(D) 4 3 -1 -1/2

39. Which is not true for the transition metal elements?

(A) Most have multiple oxidation states.
(B) Most of their compounds are gaseous.
(C) Many of their compounds are colored.
(D) Many form strong complex ions.

40. Which coupound is most likely to form intermolecular hydrogen bonds?

(A) C₃H₈
(B) CaH₂
(C) C₃H₇OH
(D) CH₃SH

41. An aqueous solution of which salt would be expected to have the most basic pH?

(A) Na₂CO₃
(B) NaC₂H₃O₂
(C) NaCl
(D) NH₄Cl

42. What is the approximate pH of an aqueous 1 x 10Ż⁹ M HCl solution?

(A) 1
(B) 5
(C) 7
(D) 9

Use the titration curve below to answer questions 43-45.

43. Which point indicates the region where the solution behaves as a buffer?

(A) A
(B) B
(C) C
(D) D

44. Which point indicates the equivalence point of the titration?

(A) E
(B) B
(C) C
(D) D

45. The titration curve best describes a titration between

(A) a strong acid and a strong base.
(B) a strong acid and weak base.
(C) a weak acid and a strong base
(D) a weak acid and a weak base.

46. Which molecule has the shortest bond length?

(A) N₂
(B) O₂
(C) Cl₂
(D) Br₂

47. An exothermic equilibrium reaction will

(A) go faster with a larger K_eq at higher temperatures.
(B) go faster with a smaller K_eq at higher temperatures.
(C) go slower with a larger K_eq at higher temperatures.
(D) go slower with a smaller K_eq at higher temperatures.

48. Consider the endothermic equilibrium reaction of BaCO₃(s) <===> BaO(s) + CO₂(g). Which would produce more BaO(s)?

(A) Decreasing the temperature.
(B) Decreasing the pressure.
(C) Adding more CO₂(g).
(D) All of the above would shift the equilibrium left.

49. If the coefficients of all species in a chemical reaction are divided in half, the reaction is still balanced. The new reaction would have an equilibrium constant with a value that is _______ the value for the first reaction.

(A) the same as
(B) twice
(C) half
(D) the square root of

50. Which crystal packing of atoms results in proportionately less unoccupied volume per unit cell?

(A) simple cubic
(B) body centered cubic
(C) face centered cubic
(D) The unoccupied volume is constant for all.

PART II

51. In the series HF, HCl, HBr, HI, the last three compounds demonstrate increasing normal boiling points with increasing molar mass, but HF possesses an unusually high boiling point, as noted in the table below. What is the reason for HF's unusual behavior?

Hydrogen halide	Boilng point
HF	+120 °C
HCl	-84.9 °C
HBr	-67.0 °C
HI	-50.8 °C

(A) dipole-dipole forces
(B) London forces
(C) hydrogen bonding
(D) instantaneous dipole-dipole forces

52. Consider two solutions: a 0.50 m solution of Ca(NO₃)₂ and a 0.75 m solution of KCl. Which statement about the solutions is correct?

(A) The potassium chloride solution has a lower freezing point because the salt concentration is greater.
(B) The calcium nitrate solution has a higher freezing point because the total ion concentration is greater.
(C) Both solutions freeze at the same temperature, which is lower than 0 °C, because they have equal ion concentrations.
(D) both solutions freeze at 0 °C because the concentration of solute is too small to cause any variation in freezing point.

53. A 0.73 mol sample of a salt of sodium is dissolved in 150 g of pure water. The boiling point of the solution is 105 °C. The most likely anion in this solution is : (K_b = 0.512 °C mŻ¹).

(A) nitrate
(B) sulfate
(C) phosphate
(D) none of these

54. Which is a base under the Arrhenius, Bronsted-Lowry and Lewis theories?

(A) NH₃
(B) OHŻ
(C) O²Ż
(D) H₂O

55. A saturated solution of Mg(OH)₂ has a molar solubility of 1.44 x 10Ż⁴ M. What is its solubility product constant, K_sp?

(A) 1.2 x 10Ż¹¹
(B) 2.1 x 10Ż⁸
(C) 3.0 x 10Ż¹²
(D) 4.2 x 10Ż⁸

56. The K_sp for Fe(IO₃)₃ is 1.0 x 10Ż¹⁴. A solution containing Fe³⁺ is mixed with a solution containing IO₃Ż, and at the instant of mixing, [Fe³⁺] = 10Ż⁴ M and [IO₃Ż] = 10Ż⁵ M. Which statement is accurate?

(A) A precipitate forms, because Q_sp > K_sp.
(B) A precipitate forms, because Q_sp < K_sp.
(C) No preciptate forms, because Q_sp > K_sp.
(D) No precipitate forms, because Q_sp < K_sp.

57. Which equation represents the standard heat of formation reaction for P₄O₁₀(s)?

(A) 2 P₂(g) + 5 O₂(g) ---> P₄O₁₀(s)
(B) 2 P₂(s) + 5 O₂(g) ---> P₄O₁₀(s)
(C) P₄(g) + 5 O₂(g) ---> P₄O₁₀(s)
(D) P₄(s) + 5 O₂(g) ---> P₄O₁₀(s)

58. Corrosion of ships can be minimized by attaching a "sacrificial plate" of zinc to the hull. This plate corrodes instead of the steel of the ship because

(A) the zinc behaves as a cathode, and is oxidized to zinc ions.
(B) the zinc behaves as an anode, and is oxidized to zinc ions.
(C) the steel hull behaves as a cathode, and is reduced to iron ions.
(D) the steel hull behaves as an anode, and is reduced to iron ions.

59. A spoon is made the cathode in an electroplating apparatus containing a AgNO₃ solution. How many grams of Ag will be plated on the spoon if a current of 2.00 A is passed through the apparatus for 1.90 min.?

(A) 0.255 g
(B) 0.150 g
(C) 0.128 g
(D) 0.0638 g

60. A cell is set up using the following reactions:

Zn | Zn²⁺ (0.5M) || Ni²⁺ (0.1 M) | Ni

Ni²⁺ + 2eŻ ----> Ni	E° = -0.250 V
Zn²⁺ + 2eŻ ----> Zn	E° = -0.763 V

What is the voltage of the cell?

(A) -0.513 V
(B) -1.013 V
(C) 0.492 V
(D) 0.513 V

61. Given the thermochemical equations

2 Cu₂O(s) + O₂(g) ---> 4 CuO(s)	DH° = -287.9 kJ
Cu₂O(s) ---> CuO(s) + Cu(s)	DH° = 11.3 kJ

What is the standard heat of formation of CuO(s)?

(A) 132.7 molŻ¹
(B) -132.7 molŻ¹
(C) 155.3 kJ molŻ¹
(D) -155.3 kJ molŻ¹

62. What is the amount of heat that is released when 8.17 g of Al(s) are converted to Al₂O₃ (s) at 25 °C and 1 atm via the reaction shown?

4 Al(s) + 3 O₂(g) ---> 2 Al₂O₃(s)
for this reaction, DH° = -3352 kJ

(A) 134 kJ
(B) 254 kJ
(C) 268 kJ
(D) 1.01 x 10³ kJ

63. What are the signs of the enthalpy and entropy for the vaporizaton of benzene?

C₆H₆(l) ---> C₆H₆(g)

DH° DS°

(A) + +

(B) + -

(C) - +

(D) - -

64. The slowest step of a reaction is called the

(A) elementary process
(B) molecularity.
(C) order.
(D) rate-determining step.

65. For a first- order reaction of half-life 150 min, what is the rate constant in minŻ¹? t_1/2 = 0.693 / k₁

(A) 0.00104
(B) 0.00462
(C) 69.3
(D) 216

66. What is the reducing agent in the forward reaction?

H₂O₂(aq) + 2 HI(aq) ---> 2 H₂O(l) + I₂(s)

(A) H₂O₂
(B) HI
(C) H₂O
(D) I₂

67. What is the hydridization of the central carbon in the compound H₂C=C=CH₂?

(A) sp
(B) sp²
(C) sp³
(D) sp³d

68. What condition describes a reaction at equilibrium?

(A) DG = 0
(B) DG° = 0
(C) DG° = DG°
(D) ln K = 0

69. What is the wavelength of green light that has a frequency of 5.2 x 10¹⁴ Hz?

(A) 155 nm
(B) 173 nm
(C) 347 nm
(D) 577 nm

70. The addition of which solution would provide the best way to distinguish between AgNO₃(aq) and Zn(NO₃)₂(aq)?

(A) H₂O
(B) HNO₃
(C) NH₃
(D) HCl