U.S. National Chemistry Olympiad: 1986 Local Section Test

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1. A strip of silver foil has a uniform width of 1.00 cm and a uniform thickness of 0.0119 cm. If the density of silver is 10.5 g/cm³, how long a strip should be cut to obtain 1.00 g of the metal?

(A) 9.52 x 10¯² cm
(B) 1.19 cm
(C) 8.00 cm
(D) 12.5 cm

2. A car traveling at 10 miles per hour emits about 0.15 kg of carbon monoxide (CO) gas per mile. How many moles of CO are emitted per mile under theses conditions?

(A) 1.5 x 10¯¹
(B) 5.4
(C) 9.4
(D) 12.5

3. You need to fertilize an area with the equivalent of 25.0 pounds of nitrogen, N. How much urea, CON₂H₄, should be used?

(A) 46.7 lb
(B) 53.6 lb
(C) 107 lb
(D) 127 lb

4. A sample of a conpound contains 0.100 g of hydrogen and 4.20 g of nitrogen. The simplest formula for the compound is

(A) HN₂
(B) HN₃
(C) NH₃
(D) NH₂

5. If the hydrocarbon C₂H₄ is burned in oxygen gas, carbon dioxide and water are formed as described by the unbalanced chemical equation

C₂H₄ + O₂ ----> CO₂ + H₂O

When this equation is balanced properly, we predict that one mole of C₂H₄ will

(A) react with one mole of O₂
(B) form two moles of CO₂.
(C) form three moles of water.
(D) react with four moles of O₂.

6. A human patient suffering from a duodenal ulcer may show a hydrochloric acid concentration of 0.080 mol/liter in his gastric juice. It is possible to neutralize this acid with aluminum hydroxide, Al(OH)₃, which reacts with HCl according to the balanced chemical equation

Al(OH)₃ + 3 HCl ----> AlCl₃ + 3 H₂O

If the patient's stomach receives 3.0 liters of gastric juice per day, how much aluminum hydroxide must he consume per day to counteract the acid?

(A) 6.2 g
(B) 19 g
(C) 26 g
(D) 78 g

7. The correct molecular formula of a compound that has an empirical formula of C₂H₂O and a molecular weight of 168 is

(A) C₂HO
(B) C₄H₂₄O₆
(C) C₈H₈O₄
(D) C₈H₁₂O₅

8. Given the reaction

Na₂O(s) + H₂O(l) -----> 2 NaOH(aq)

what is the molarity of the solution formed if 1.35 g of Na₂O is mixed with water such that the final volume is 100 mL?

(A) 0.0435 M
(B) 0.108 M
(C) 0.217 M
(D) 0.435 M

9. When ignited in air, magnesium burns with a bright flame to form magnesium oxide. The standard heat of formation of solid MgO is -1203 kJ/mol. How much heat is evolved when sufficient magnesium meal is burned in oxygen to form 1.0 g of MgO?

(A) 0.025 kJ
(B) 30 kJ
(C) 40 kJ
(D) 1203 kJ

10. ⁴⁰Ca, ³⁹K, and ⁴¹Sc all have the same

(A) number of electrons.
(B) atomic number.
(C) mass number.
(D) number of neutrons.

11. 1s²2s²2p⁶3s²3p⁶3d³4s² is the ground state electonic configuration of

(A) Ca
(B) Sc
(C) Zn
(D) V

12. The first ionization energy for a mole of magnesium atoms is the energy required for the process

(A) Mg(s) ----> Mg(g)
(B) Mg(g) ----> Mg⁺(g) + 2e¯
(C) Mg⁺(g) -----> Mg²⁺(g) + e¯
(D) Mg(g) ------> Mg⁺(g) + e¯

13. Element x, whose atoms have an outer-shell electron configuration ns²np⁴, is most likely to react chemically to form ions which have a charge of

(A) +2e
(B) +e
(C) -e
(D) -2e

14. The formula of the compound ammonium carbonate is

(A) NH₄CO₃
(B) NH₄CO₄
(C) NH₄HCO₃
(D) (NH₄)₂CO₃

15. Which statement regarding the properties of elements arranged in the Periodic Table is correct?

(A) Atomic sizes decrease going down a Group or Family.
(B) Atomic sizes increase going from Fr in Group I to F in Group VII.
(C) Atomic sizes decrease going from left to right in a Period.
(D) All atoms in the same Group have the same size.

16. In their stable compounds, alkaline earth metals normally exist as

(A) M⁺ cations
(B) M²⁺ cations
(C) M atoms
(D) M¯ anions

17. Hydrogen trioxide, H₂O₃, a highly unstable and reactive compound related to hydrogen peroxide, has been prepared recently in small amounts. Which Lewis electron dot structure is most likely to represent the structure of hydrogen trioxide?

18. The most likely molecule to be formed by the reaction of boron and chlorine is

(A) BCl
(B) BCl₃
(C) BCl₄
(D) BCl₆

19. In which compound would the molecules be expected to be linear?

(A) O₃
(B) SO₂
(C) H₂O
(D) CO₂

20. The shortest bond is that in

(A) F₂
(B) O₂
(C) N₂
(D) C₂

21. Which is the most electronegative atom?

(A) P
(B) Al
(C) Cl
(D) S

22. The closest verbal description of the shape of the NH₃ molecule (defined by the positions of the atomic nuclei) is

(A) tetrahedral
(B) non-linear
(C) trigonal planar
(D) trigonal pyramid

23. Which of these molecules is octahedral?

(A) SF₄
(B) SF₆
(C) ClF₃
(D) BrF₅

24. Given the reactions

what is DH° for the reaction

CH₄(g) + O₂(g) ----> CO₂(g) + H₂O(g)?

(A) -1453.9 kJ
(B) -326.9 kJ
(C) -236.6 kJ
(D) +118.3 kJ

25. 500 mL of a gaseous compound weighs 0.9825 gram at 0 °C and 760 torr. What is the approximate molecular weight of the compound in g/mol?

(A) 19.7
(B) 38. 7
(C) 44.0
(D) 58.9

26. What is the number of molecules in 1.00 mL of an ideal gas at STP?

(A) 2.69 x 10²²
(B) 6.02 x 10²⁰
(C) 2.69 x 10¹⁹
(D) 22.4 x 10¹⁹

27. If 6.60 g of a gaseous compound occupy a volume of 1.20 L at 27 °C and 0.967 atm, the molecular weight of the compound is

(A) 109 g/mol.
(B) 123 g/mol.
(C) 140 g/mol.
(D) 165 g/mol.

28. How many liters of hydrogen gas at STP can be produced by the reactionof 9.00 g of Al with excess dilute H₂SO₄?

2 Al(s) + 3 H₂SO₄(aq) -----> 3 H₂(g) + Al₂(SO₄)₃

(A) 5.61 L
(B) 11.2 L
(C) 33.6 L
(D) 67.2 L

29. Which substance has the highest boiling point?

(A) CH₄
(B) He
(C) HF
(D) Cl₂

30. When sugar is dissolved in water, the resulting solution

(A) has a higher freezing point than pure water.
(B) has a higher boilng point than pure water.
(C) has a higher vapor pressure than pure water.
(D) has a lower osmotic pressure than pure water.

31. The process of dissolving solid ammonium nitrate in water is endothermic. Which statement is true?

(A) The solubility of ammonium nitrate becomes larger at higher temperatures.
(B) The solubility of ammonium nitrate becomes lower at higher temperatures.
(C) The solubility of ammonium nitrate is not affected by temperature.
(D) One cannot predict the solubility behavior of ammonium nitrate from the information given.

32. A compound containing an oxygen atom in the +2 oxidation state is

(A) OF₂
(B) H₂O
(C) K₂O₂
(D) Li₂O

33. In the reaction

6 KI + 2 KMnO₄ + 4 H₂O ------> 3 I₂ + 2 MnO₂ + 8 KOH

which atom undergoes oxidation?

(A) K
(B) Mn
(C) O
(D) I

34. For the unbalanced oxidation-reduction reaction

Ag₂S(s) + NO₃¯ (aq) ----> Ag⁺ (aq) + S(s) + NO(g)

which takes place in an acidic solution, what is the balanced half-reaction for the process that involves reduction?

(A) Ag₂S(s) ---> 2 Ag⁺(aq) + S(s) + NO(g)
(B) S²¯(aq) ---> S(s) + 2e¯
(C) NO₃¯ (aq) + 4 H⁺(aq) + 3e¯ ---> NO(g) + 2 H₂O(l)
(D) NO₃¯ (aq) + 2 H⁺(aq) + 2e¯ ---> NO(g) + 2 OH¯(aq)

35. In the Arrhenius picture of acids and bases, the reaction of an acid with a base always results in the formation of

(A) H⁺
(B) OH¯
(C) CO₂
(D) H₂O

36. A basic oxide is

(A) CaO
(B) N₂O₅
(C) CO₂
(D) SiO₂

37. A standard solution of 0.165 M HCl is being used to determine the concentration of an unknown NaOH solution. If 25.5 mL of the acid solution are required to neutralize 15.0 mL of the base, what is the molarity of the NaOH solution?

(A) (0.165) / (25.5 + 15.0) M
(B) (15.0) / (0.165) (25.5) M
(C) (0.165) (15.0 / 25.5) M
(D) (0.165) (25.5 / 15.0) M

38. The half-life of radioactive ⁵⁵Cr is 1.8 hours. The delivery of a sample of this isotope from the reactor to your laboratory requires about 10.8 hours. What is the minimum amount of such material that should be shipped in order that you receive 1.0 milligram of ⁵⁵Cr?

(A) 128 mg
(B) 64 mg
(C) 32 mg
(D) 11 mg

39. A catalyst that increases the rate of a reaction does so by

(A) increasing the concentrations of the initial reactants
(B) increasing the temperature
(C) decreasing the temperature
(D) decreasing the activation energy for the process

40. Seawater contains a fairly high concentration of Mg²⁺(aq) ion, about 0.05 M. Seawater therefore would not be expected to contain very large concentrations of

(A) Cl¯
(B) SO₄²¯
(C) K⁺
(D) OH¯

41. 500 mL of 0.020 M BaCl₂(aq) is added to 500 mL of 0.020 M NaF(aq). K_sp = 2 x 10¯⁶ for BaF₂ in water.

(A) The solutions mix without reaction
(B) A precipitate of BaF₂(s) is formed when the solutions are mixed
(C) Undissolved BaCl₂ solid dissolves when the solutions are mixed
(D) The concentrations of all the ions in the final solution are 2 x 10¯⁶ M.

42. Which aqueous solution should be neutral?

(A) NH₄Cl
(B) Na(ClO₄)₂
(C) KCN
(D) NaHSO₄

43. The pH of a solution of vinegar is 3.00. The concentration of OH¯ ion in this solution is

(A) 3.00 M
(B) 1 x 10¯³ M
(C) 1 x 10¯¹¹ M
(D) 17 M

44. The indicator ravishing red has a color change from yellow to red in the pH range 6.5- 7.5. This indicator would be used to titrate

(A) a weak acid with a strong base
(B) a strong acid with a weak base
(C) a weak acid with a weaker acid
(D) a strong acid with a strong base

45. If the K_a of a weak acid is 5 x 10¯⁴, the pH of a 0.2 M solution of the acid will be about

(A) 0.7
(B) 2.0
(C) 3.3
(D) 7.0

46. Given the standard electrode (reduction) potentials:

What would be the E° for a cadmium-silver cell?

(A) 0.4 v
(B) 0.5 v
(C) 1.2 v
(D) 2.0 v

47. Consider the following reaction at equilibrium in a container of constant volume:

Which of the following would result in a greater concentration of SO₂?

(A) addition of O₂
(B) addition of SO₃
(C) removal of SO₃
(D) a decrease in temperature

48. A current of 10.0 amperes flows for 2.00 hours through an electrolytic cell containing a molten salt of metal x. This results in the decomposition of 0.250 mole of metal x at the cathode. The oxidation state of x in the molten salt is

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

49. In a voltaic cell, oxidation occurs at the

(A) anode
(B) cathode
(C) salt bridge
(D) electrode at which electrons enter from the outside

50. The free energy change for the chemical reaction that occurs in a voltaic cell when it is discharging and producing an electric current must be

(A) positive
(B) negative
(C) zero
(D) unpredictable

51. The average distance of an electron in a hydrogen atom from the nucleus is indicated by the quantum number

(A) n
(B) m_l
(C) l
(D) m_s

52. "Wood alcohol" (methyl alcohol or methanol), CH₄O, is toxic and is used as a denaturant in industrial grain alcohol and as a fuel. A satisfactory Lewis structure for this compound is

53. In the SiH₄ molecule, the Si atomic orbitals used in forming covalent bonds are best described as

(A) one s and three p atomic orbitals
(B) four sp³ hybrid orbitals
(C) four d²sp³ hybrid orbitals
(D) three sp² orbitals and one p orbital

54. The triple bond in the N₂ molecule can be described as

(A) two bonding and one antibonding sigma bonds
(B) three sigma bonds
(C) one sigma and two pi bonds
(D) two bonding and one antibonding pi bonds

55. Which one of the following is not the expected geometry of the indicated molecule or ion?

(A) CCl₄ - regular tetrahedron
(B) BeCl₂ - linear
(C) SO₃ - triangular pyramid
(D) CH₂O - trigonal planar

56. A 0.10 molal aqueous solution of HF shows a freezing point of -0.198 °C. What is the percent dissociation of HF into ions in this solution? (K_f = 1.86 for water)

(A) 6.4%
(B) 10%
(C) 20%
(D) 98%

57. Which one of these solid substances has a crystal structure containing separate discrete molecules?

(A) Dry ice
(B) Graphite
(C) Quartz
(D) Silver bromide

58. A solution of a non-electrolyte, x, contains 84 grams of x per kilogram of water and freezes at -1.46°C. What is the molecular weight of x? (K_f = 1.86)

(A) 84 x 1.86 x 1.46 = 222 g/mol
(B) 84 x (1.86 / 1.46) = 107 g/mol
(C) 84 x (1.46 / 1.86) = 66 g/mol
(D) 1.46 x (1.86 / 84) = 0.032 g/mol

59. A 1.20 liter sample is drawn from a bottle labeled "86.0% by weight H₂SO₄, density 1.787 g/mL". What is the molarity of the sample?

(A) 8.78 M
(B) 10.5 M
(C) 15.7 M
(D) 18.2 M

60. Which substance is most soluble in water?

(A) C₆H₆
(B) CH₃OH
(C) CO₂
(D) CH₄

61. 2.80 grams of a monoprotic weak acid, HX, was dissolved in water. Titration of the acid to its equivalence point required 29.2 mL of 0.500 M NaOH solution. What is the molecular weight of the acid, HX?

(A) 192 g/mol
(B) 164 g/mol
(C) 96.0 g/mol
(D) 5.21 g/mol

62. The ionic reaction

3 I¯ + S₂O₈²¯ ---> 2 SO₄²¯ + I₃¯

is found to be described by the experimental rate equation

rate = k[I¯] [S₂O₈²¯]

This suggests that

(A) the reaction occurs when three iodide ions collide simultaneous with one S₂O₈²¯ ion
(B) there must be only one step in the overall reaction since the rate is first-order in both reactants
(C) the rate of reaction is inhibited by the presence of I₃¯
(D) a slow step in the overall reaction sequence may involve the collision of a single I¯ ion with a single S₂O₈²¯ ion

63. The hemoglobin from the red corpuscles of most mammals contains approximately 0.33% iron by weight. If physical measurements indicate a molecular weight for hemoglobin of 68000 g/mol, how many iron atoms are there in each molecule of hemoglobin? (AW Fe= 56)

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

64. Given the following standard enthalpies of formation in kJ/mol:

CO₂ -393.3, CH₃OH -238.5, H₂O -285.3.

What is the heat of combustion of methanol, CH₃OH, in kJ/mol?

(A) -725.4
(B) -154.8
(C) -140.8
(D) 154.8

65. An element whose neutral atoms would be expected to be paramagnetic is

(A) neon
(B) fluorine
(C) magnesium
(D) zinc

66. The heat of formation of gaseous water molecules is -241.8 kJ/mol. If the H-O bond energy is 463 kJ/mol and the H-H bond energy is 435 kJ/mol, what is the energy of the bond between oxygen atoms in the O₂ molecule in kJ/mol?

(A) 0
(B) 249
(C) 428
(D) 498

67. The osmotic pressure of an aqueous solution containing 30.0 g of a newly-isolated protein in one liter of solution is 12.7 torr at 25 °C. What is the approximate molecular weight of the protein in g/mol?

(A) 58
(B) 333
(C) 4000
(D) 44000

68. Carbon dioxide is a gas at room temperature while silicon dioxide is a high-melting solid. The best explanation of this difference is that

(A) Si has more electrons than C
(B) the atoms in CO₂ are bound by covalent bonds while SiO₂ is an ionic compound
(C) van der Waals' forces are stronger in SiO₂
(D) CO₂ consists of discrete molecules while in SiO₂ atoms are joined by a network of covalent bonds

69. 2.00 moles of NO and an undetermined amount of O₂ are placed in a one-liter container at 460 °C. When the reaction

2 NO(g) + O₂(g) <===> 2 NO₂(g)

reaches equilibrium, we find 0.00156 mol of O₂ and 0.500 mol of NO₂. The value of the equilibrium constant for this system is

(A) 4.42
(B) 40.1
(C) 71.2
(D) 214

70. Proteins are macromolecules in which the simplest repeating structural units are

(A) nucleic acids
(B) amino acids
(C) purines
(D) carbohydrates