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U.S. National Chemistry Olympiad

1996 Local Section Test

Notes


1. Which gas is both diatomic and colored?

(A) carbon monoxide
(B) chlorine
(C) nitrogen dioxide
(D) oxygen

2. Which formula represents a peroxide?

(A) Li2O
(B) SiO2
(C) Na2SiO3
(D) BaO2

3. Which statement about the halogen family is true?

(A) Each of the halogens can be obtained by the electrolysis of its respective molten halide salt.
(B) Iodine is the strongest oxidizing agent.
(C) Bromine is obtained by oxidation using chloride ions as the oxidizing agent.
(D) Halide ions are generally more reactive than the parent halogens.

4. All of these substances are important industrial reducing agents except

(A) C
(B) CO
(C) CO2
(D) H2

5. What is the general formula for the alkali metal hydrides?

(A) MH
(B) MOH
(C) MH2
(D) M(OH)2

6. Each of three samples was weighed on a different balance. The masses of the three are 1.028 kg, 82.9 g, and 45.1 mg. The sum of the three masses should be reported as

(A) 1110.9451 g
(B) 1111 g
(C) 110 g
(D) 1.11 x 103 g

7. Magnetite, Fe3O4, is a mixture of iron(II) oxide and iron(III) oxide. What is the most likely ratio of iron(II) oxide to iron(III) oxide in magnetite?

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

8. A student wishes to prepare 250.mL of a 0.200 M solution of Na2SO4. Which of these procedures should be followed?

Substance Molar Mass
Na2SO4 142 g mol¯1

(A) 28.4 g of Na2SO4 should be dissolved in 250. mL of water in a large bottle.
(B) 250. mL of water should be added to 28.4 g of Na2SO4 in a large bottle.
(C) 7.10 g of Na2SO4 should be dissolved in enough water to fill a graduated beaker to the 250. mL mark.
(D) 7.10 g of Na2SO4 should be dissolved in a small amount of water and diluted to 250. mL in a volumetric flask.

9. How many moles of ozone, O3, could be formed from 48.0 g of oxygen gas, O2?

(A) 1.00 mol
(B) 1.30 mol
(C) 1.50 mol
(D) 2.00 mol

10. How many grams of carbon are present in 0.50 mol of sucrose (C12H22O11)?

Substance Molar Mass
C12H22O11 342 g mol¯1

(A) 60 g
(B) 72 g
(C) 90 g
(D) 120 g

11. If excess Ca(OH)2 is treated with 0.160 mol of dry HCl gas, what is the maximum number of grams of CaCl2 that could be formed?

Substance Molar Mass
Ca(OH)2 74.1 g mol¯1
HCl 36.5 g mol¯1
CaCl2 111.0 g mol¯1

(A) 35.5 g
(B) 17.8 g
(C) 8.88 g
(D) 4.44 g

12. What volume of 0.500 M CaCl2 solution is needed to prepare 250 mL of solution that has a chloride concentration of 0.100 M?

(A) 12.5 mL
(B) 25.0 mL
(C) 50.0 mL
(D) 100 mL

13. Which group II element would be expected to be the hardest?

(A) Be
(B) Mg
(C) Ca
(D) Ba

14. Chlorine reacts with fluorine above 200 °C to form chlorine trifluoride, ClF3, as shown by this equation:

Cl2(g) + 3F2(g) ---> 2ClF3(g)

If equal numbers of moles of chlorine and fluorine are combined, the maximum number of moles of ClF3 that could be formed will be equal to

(A) the number of moles of Cl2.
(B) the number of moles of F2.
(C) twice the number of moles of Cl2.
(D) two-thirds the number of moles of F2.

15. An acidic solution of permanganate ions reacts with oxalate ions to form manganese(II) ions and carbon dioxide, as shown in this equation.

2 MnO4¯ + 5 C2O42¯ + 16 H+ ---> 2 Mn2+ + 10 CO2 + 8 H2O

If 31.72 mL of 0.0840 M potassium permanganate solution exactly reacts with 25.00 mL of sodium oxalate solution, what is the original oxalate ion concentration?

(A) 0.0426 M
(B) 0.107 M
(C) 0.213 M
(D) 0.266 M

16. What is true about the relative freezing points of these three substances?

I. Water
II. 0.1 M acetic acid (HC2H3O2) solution
III. 0.1 M sodium acetate (NaC2H3O2) solution

(A) III < II < I
(B) II < III < I
(C) II = III < I
(D) II < III = I

17. Which increases as a gas is heated at constant volume?

(A) size of the molecules
(B) potential energy of the molecules
(C) kinetic energy of the molecules
(D) attractive forces between molecules

18. What is the name of the process that occurs at a system is changed from point A to point B in this phase diagram?

(A) condensation
(B) evaporation
(C) fusion
(D) sublimation

19. When these substances (C, CO2, C6H12O6, and CaC2) are arranged in order of increasing melting point (with the lowest melting substance first), the correct order is

(A) C < CO2 < C6H12O6 < CaC2
(B) C6H12O6 < CaC2 < CO2 < C
(C) C < CO2 < CaC2 < C6H12O6
(D) CO2 < C6H12O6 < CaC2 < C

20. What will happen to the volume of a bubble of air found underwater in a lake, where the temperature is 15 °C and the pressure is 1.5 atm, if the bubble then rises to the surface where the temperature is 25 °C and the pressure is 1.0 atm?

(A) Its volume will become greater by a factor of 2.5.
(B) Its volume will become greater by a factor of 1.6.
(C) Its volume will become greater by a factor of 1.1.
(D) Its volume will become smaller by a factor of 0.70.

21. Which of these Group IV (IUPAC Group 14) solids has the greatest electrical conductivity at 25 degrees C?

(A) C
(B) Si
(C) Ge
(D) Pb

22. The standard enthalpy of formation ([delta]H°f) for sodium bromide is the enthalpy change for the reaction

(A) Na+(g) + Br¯(g) --> NaBr(g)
(B) Na+(g) + Br¯(g) --> NaBr(s)
(C) 2 Na(s) + Br2(g) --> 2 NaBr(s)
(D) Na(s) + 1/2 Br2(l) --> NaBr(s)

23. Use the standard enthalpies of formation in the table to calulate [delta]H° for this reaction:

2 CrO42¯(aq) + 2 H+(aq) --> Cr2O72¯(aq) + H2O(l)

Substance [delta]H°f, kJ mol¯1
CrO42¯(aq) - 881.2
Cr2O72¯(aq) - 1490.3
H+(aq) 0
H2O(l) - 285.8

(A) 272.1 kJ
(B) 13.7 kJ
(C) -13.7 kJ
(D) -272.1 kJ

24. For which of these processes is the value of [delta]S expected to be negative?

I. Sugar is dissolved in water
II. Steam is condensed
III. CaCO3 is decomposed into CaO and CO2.

(A) I only
(B) I and III only
(C) II only
(D) II and III only

25. Which set of conditions is most likely to result in a reaction that is spontaneous as written?

  [delta]H [delta]S T
(A) < 0 < 0 500 °C
(B) < 0 < 0 0 °C
(C) > 0 < 0 0 °C
(D) > 0 < 0 500 °C

26. What can be correctly said about the energy of activation for a reversible exothermic reaction? The energy of activation

(A) is greater for the reverse reaction than for the forward reaction.
(B) is greater for the forward reaction than for the reverse reaction.
(C) is the same for the reaction in both directions.
(D) for the two directions of this reaction cannot be compared without doing experiments.

27. The reaction of nitrogen monoxide, NO, with hydrogen, H2, is represented by this equation:

2 NO(g) + 2 H2(g) ---> N2(g) + 2 H2O(g)

The reaction obeys this rate law:

Rate = k[NO]2[H2]

If [NO] is tripled and [H2] is doubled, how will the rate be affected?

(A) The rate will be increased by a factor of six.
(B) The rate will be increased by a factor of twelve.
(C) The rate will be increased by a factor of eighteen.
(D) The rate will be increased by a factor of thirty-six.

28. Which of these changes with time for a first-order reaction?

I. rate of reaction
II. rate constant
III. half-life

(A) I only
(B) III only
(C) I and II only
(D) II and III only

29. Under certain conditions, the average rate of appearance of oxygen gas in the reaction:

2 O3(g) ---> 3 O2(g)

is 1.2 x 10¯3 atm sec¯1. What is the average rate, expressed in units of atm sec¯1, for the disappearance of O3?

(A) 1.2 x 10¯3
(B) 1.8 x 10¯3
(C) 8.0 x 10¯4
(D) 5.3 x 10¯3

30. The experimental data from a certain reaction gives these three graphs. What is the most likely order for this reaction.

(A) zero
(B) first
(C) second
(D) third

31. For irreversible reactions, the rate will be affected by changes in all of these factors except

(A) temperature.
(B) concentration of reactants.
(C) presence of a catalyst.
(D) concentration of products.

32. What is the equilibrium expression for the decomposition of ammonium carbamate, NH4CO2NH2, that occurs according to this equation:

NH4CO2NH2(s) <===> 2 NH3(g) + CO2(g)

(A) K = [NH3][CO2]
(B) K = [NH3]2[CO2]
(C) K = [NH3][CO2] / [NH4CO2NH2]
(D) K = [NH3]2[CO2] / [NH4CO2NH2]

33. Which factors will affect both the position of equilibrium and the value of the equilibrium constant for this reaction? The [delta]H = - 92 kJ

N2(g) + 3 H2(g) <===> 2 NH3(g)

(A) increasing the volume of the container
(B) adding N2
(C) removing NH3
(D) lowering the temperature

34. According to the Brønsted-Lowry definition, a base is a substance that

(A) increases the hydroxide ion concentration in water.
(B) can react with water to form OH¯ ions.
(C) can donate an electron pair to form a covalent bond.
(D) can accept a proton from an acid.

35. What is the pH of a 0.02 M solution of KOH?

(A) 12.3
(B) 12.0
(C) 2.0
(D) 1.7

36. Which couple is not a conjugate acid-base pair?

(A) HCO3¯ and CO32¯
(B) H3O+ and H2O
(C) H2PO4¯ and PO43¯
(D) NH3 and NH2¯

37. These acids are listed in order of decreasing acid strength in water.

HI > HNO2 > CH3COOH > HCN

According to the Brønsted-Lowry theory, which anion is the weakest base?

(A) I¯
(B) NO2¯
(C) CH3COO¯
(D) CN¯

38. What is the [H+] in a 0.40 M solution of HOCl?

Substance Equilibrium Constant, Ka
HOCl 3.5 x 10¯8

(A) 1.4 x 10¯8 M
(B) 1.2 x 10¯4 M
(C) 1.9 x 10¯4 M
(D) 3.7 x 10¯4 M

39. Which of these salts will give a basic solution when added to water?

(A) NH4NO3
(B) NH4C2H3O2
(C) Ca(NO3)2
(D) Ca(C2H3O2)2

40. BaSO4 and BaCO3 are slightly soluble salts with comparable Ksp values in water. Which salt(s) will be more in a 1.0 M solution of HNO3 than in water?

(A) BaSO4 only
(B) BaCO3 only
(C) both BaSO4 and BaCO3
(D) neither BaSO4 or BaCO3

41. Which change represents a reduction process?

(A) ClO¯ ---> ClO3¯
(B) N2O ---> N2O4
(C) NO ---> NH3
(D) HCrO4¯ ---> CrO42¯

42. When these species (SO2, PbS, and Na2S2O3) are listed in order of increasing oxidation number of the sulfur atoms (most negative to most positive oxidation number), the correct order is

(A) PbS, Na2S2O3, SO2
(B) PbS, SO2, Na2S2O3
(C) Na2S2O3, PbS, SO2
(D) SO2, Na2S2O3, PbS

43. Use these reduction potentials to determine which one of the reactions below is spontaneous.

Reaction Reduction Potentials, E°
Ag+ + e¯ ---> Ag 0.800 V
Pb2+ + 2e¯ ---> Pb - 0.126 V
V2+ + 2e¯ ---> V - 1.18 V

(A) V2+ + 2 Ag ---> V + 2 Ag+
(B) V2+ + Pb ---> V + Pb2+
(C) 2 Ag+ + Pb2+ ---> 2 Ag + Pb
(D) 2 Ag+ + Pb ---> 2 Ag + Pb2+

44. It is possible to produce chlorine gas by electrolyzing any of these chlorine-containing compounds under the proper conditions. Which compound will require the smallest number of coulombs to produce one mole of chlorine?

(A) Ca(OCl)2
(B) NaClO2
(C) KClO3
(D) Mg(ClO4)2

45. A monatomic species that has 18 electrons and a net charge of 2¯ has

(A) the same number of electrons as a neutral argon atom.
(B) more protons than electrons.
(C) 2 unpaired electrons.
(D) 20 protons

46. Based on its electron configuration, the element that is most similar in chemical properties to selenium is

(A) As
(B) Cl
(C) Sb
(D) Te

47. How many electrons in a silver atom have n = 3 and l = 2 ?

(A) 2
(B) 8
(C) 10
(D) 18

48. The neutral atom with the largest radius is

(A) K
(B) Mg
(C) As
(D) Br

49. Which of these electron diagrams could represent the ground state of the p valence electrons of carbon?

50. All of these molecules are polar except

(A) H2O
(B) CO2
(C) NO2
(D) SO2

51. Which species contains a central atom with sp2 hybridization?

(A) NI3
(B) CIF3
(C) O3
(D) I3¯

52. Electrostatic forces between oppositely charges are greatest in

(A) CaO
(B) MgO
(C) CaS
(D) MgS

53. Which substance has the lowest boiling point?

(A) HCl
(B) H2S
(C) PH3
(D) SiH4

54. How do the magnitudes of the H-N-H bond angles vary in these species?

(A) NH2¯ < NH3 < NH4+
(B) NH2¯ < NH4+ < NH3
(C) NH3 < NH2¯ < NH4+
(D) NH3 < NH4+ < NH2¯

55. Which molecule has the greatest bond energy

(A) CO
(B) O2
(C) NO
(D) F2

56. Which formula most likely represents an alkene?

(A) C2H2
(B) C3H8
(C) C4H8
(D) C6H6

57. All of these classes of compounds contain a carbonyl functional group except

(A) carboxylic acids.
(B) amides.
(C) ethers.
(D) ketones.

58. How many different compounds have the formula C5H12?

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

59. An ester is formed by the reaction between

(A) two acids.
(B) two alcohols.
(C) two aldehydes.
(D) an acid and an alcohol.

60. Which of these is formed by condensation polymerization?

I. Nylon
II. Teflon®

(A) I only
(B) II only
(C) both I and II
(D) neither I nor II

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