U.S. National Chemistry Olympiad: 1988 National Test

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1. A verbal statement or a mathematical equation that summarizes a broad variety of observations and experience is called a(n)

(A) hypothesis
(B) law
(C) theory
(D) evolution

2. The term that is related to the reproducibility or repeatability of a measurement is:

(A) accuracy
(B) systematic
(C) precision
(D) qualitative

3. A sample of carbon dioxide that undergoes a transformation from solid to liquid to gas would undergo

(A) a change in mass
(B) a change in density
(C) a change in composition
(D) no change in physical properties

4. A solution is a(n)

(A) compound
(B) pure substance
(C) homogeneous mixture of substances
(D) heterogeneous mixture of substances

5. Dalton's theory of atoms consisted of all of the following postulates except

(A) elements are composed of indivisible particles called atoms.
(B) atoms of different elements have different properties.
(C) atoms combine in fixed ratios of whole numbers.
(D) the volumes of gases consumed and produced are in ratios of small whole numbers.

6. Cathode rays are

(A) a beam of positively charged particles.
(B) nuclei of helium atoms
(C) fast-moving neutrons
(D) streams of electrons

7. There are two stable isotopes of carbon. They differ with respect to

(A) atomic mass
(B) number of protons
(C) atomic number
(D) electron configuration

8. One ⁴⁰Ca²⁺ ion contains

(A) 2 protons
(B) 18 electrons
(C) 21 neutrons
(D) 2 electrons

9. The average atomic weight of elemental copper is reported as 63.5. Copper consists of two stable isotopes, ⁶³Cu and ⁶⁵Cu. Approximately what percent of naturally occurring copper is the ⁶³Cu isotope?

(A) 30
(B) 50
(C) 70
(D) 90

10. The best molecular formula for sulfur in its naturally occurring state is

(A) S
(B) S₂
(C) S₆
(D) S₈

11. The correct formula for iron(III) sulfide is

(A) Fe₃S₂
(B) FeS
(C) Fe₂S₃
(D) Fe₃S

12. What is the percentage by weight of potassium in the compound KNO₃?

(A) 38.7
(B) 39.1
(C) 56.6
(D) 63.1

13. If 18.5 moles of the liquid compound C₂Cl₄ are required for a particular chemical reaction, what volume should be taken? The density of C₂Cl₄ is 1.63 g/ml.

(A) 11.3 mL
(B) 30.2 mL
(C) 1.88 L
(D) 5.01 L

14. The principle of DuLong and Petit states that the product of the atomic weight of a solid element and its specific heat, measured at room temperature, is approximately 6.2 calories per mole per degree (25.9 Joules per mole per degree). A prospector has asked you to identify the most abundant element in a mineral sample he has found. You chemically separate the most abundant element and determine that its specific heat is 5.24 x 10¯² cal per gram per degree. The element most likely is

(A) Au
(B) Fe
(C) Ni
(D) Sn

15. In the complete combustion of octane with oxygen, represented by the unbalanced chemical equation,

C₈H₁₈ + O₂ ----> CO₂ + H₂O

one gram of octane will yield what mass of water?

(A) 0.079 g
(B) 1.4 g
(C) 18 g
(D) 162 g

16. The first chemical compound of a rare gas element was prepared in 1962. Since then several such compounds have been prepared and characterized. What is the empirical formula of a compound of Xe which is 67.2% Xe and 32.8% O by mass?

(A) XeO₂
(B) XeO₃
(C) XeO₄
(D) XeO₅

17. The commercial production of phosphoric acid from phosphate ores can be represented by the equation

Ca₃(PO₄)₂ + 3 SiO₂ + 5 C + 5 O₂ + 3H₂O ---> 3 CaSiO₃ + 5 CO₂ + 2 H₃PO₄.

If 1.0 kg. each of calcium phosphate and silica are used with sufficient excess of carbon, oxygen, and water, what quantity of phosphoric acid can be produced?

(A) 0.31 kg
(B) 0.63 kg
(C) 1.0 kg
(D) 1.1 kg

18. A power company burns approximately 474 tons of coal per day to produce electricity. If the sulfur content of the coal is 1.30% by weight, how many tons of SO₂ are dumped into the atmosphere each day?

(A) 12.3
(B) 6.16
(C) 3.08
(D) 0.19

19. A 50.0 mL aliquot of a sulfuric acid solution was treated with barium chloride and the resulting BaSO₄ was isolated and weighted. If 0.667 gram of BaSO₄ was obtained, what was the morality of the H₂SO₄?

(A) 0.00700 M
(B) 0.0286 M
(C) 0.0572 M
(D) 1.43 M

20. Which statement about the electron configuration of electrons in the Cs atom is correct?

(A) The outermost two electrons are paired in the same atomic orbital.
(B) The 4f shell is completely full.
(C) Only one of the 55 electrons is involved in most interactions of Cs with other atoms.
(D) The 4f shell is only partially filled.

21. Those elements in which unpaired valence electrons are in atomic orbitals designated by l = 2 are described as

(A) representative elements.
(B) lanthanide elements.
(C) transition elements.
(D) halogens.

22. Which of the following species is smallest is size?

(A) Cl
(B) I
(C) Cl¯
(D) I¯

23. Which atom has the lowest second ionization energy?

(A) Mg
(B) Na
(C) K
(D) Ar

24. What formula would be expected for a binary compound formed between strontium and nitrogen?

(A) SrN
(B) Sr₂N
(C) SrN₃
(D) Sr₃N₂

25. The formation of an ionic compound from its elements can be understood in terms of steps, each involving a certain energy input or output. Which energy step usually dominates all others in the formation of a stable ionic compound?

(A) ionization energy
(B) electron affinity
(C) lattice energy
(D) dissociation energy

26. Which compound violates the simple octet rule for electron distribution around the central atom?

(A) CO₂
(B) NF₃
(C) OF₂
(D) PF₅

27. Predict the Cl-Sn-Cl bond angles in SnCl₃¯.

(A) 90°
(B) 109°
(C) 180°
(D) between 90° and 109°

28. The ethylene molecule, C₂H₄, is

(A) linear.
(B) planar.
(C) pyramidal.
(D) shaped like two tetahedra joined at the points.

29. Which diatomic molecular species should have the greatest bond dissociation energy?

(A) H₂
(B) F₂
(C) NO
(D) N₂

30. If a sample of silicon is "doped" with a small amount of boron, what sort of material results?

(A) insulator
(B) metallic conductor
(C) n-type semiconductor
(D) p-type semiconductor

31. Tin(II) chloride is a solid with a melting point of 246 °C; tin(IV) chloride is a liquid with a freezing point of - 33 °C. These properties can be explained by

(A) the greater covalence of SnCl₄ compared with that of SnCl₂.
(B) the greater formula weight of SnCl₄ compared with that of SnCl₂.
(C) the greater degree of ionic character of SnCl₄ compared with that of SnCl₂.
(D) the greater number of ionic and molecular particles in SnCl₄ with SnCl₂.

32. The Haber process for preparing ammonia involves the direct conversion of hydrogen and nitrogen gases at high temperature and pressure using a catalyst:

N₂(g) + 3 H₂(g) ----> 2 NH₃(g)

How many liters of ammonia could be prepared from a mixture of 19.0 liters of nitrogen and 34.7 liters of hydrogen, assuming complete conversion and with identical conditions of temperature and pressure?

(A) 19.0
(B) 23.1
(C) 34.7
(D) 38.0

33. A sample of gas confined in a bulb at 1 atm pressure and 25 °C is measured to have a density of 1.309 grams per liter. The gas is

(A) O₂
(B) N₂
(C) Ne
(D) CH₄

34. The diagram below represents a 2-dimensional model of a sample of water at a particular temperature.

Which diagram best represents the same system following the addition of a sample of crystalline urea (NH₂CONH₂)?

35. A solution is prepared by dissolving 1.20 g of sodium bisulfate, NaHSO₄, in 1.00 kg of distilled water. The osmotic pressure of the solution is determined to be 364 mm Hg or 0.48 atm. Which equation best describes how sodium bisulfate behaves in water?

(A) NaHSO₄(s) + H₂O(l) ---> will not dissolve
(B) NaHSO₄(s) + H₂O(l) ---> NaHSO₄(aq)
(C) NaHSO₄(s) + H₂O(l) ---> Na⁺(aq) + HSO₄¯(aq)
(D) NaHSO₄(s) + H₂O(l) ---> Na⁺(aq) + H⁺(aq) + SO₄²¯(aq)

36. Given the following standard enthalpies of formation: CO₂(g), -394 kJ/mol; H₂O(l), -286 kJ/mol; C₄H₃(g), 16.0 kJ/mol. Calculate the heat of combustion of one mole of C₄H₃ if the equation describing the process is

C₄H₃(g) + 6 O₂ ---> 4 CO₂(g) + 4 H₂O(l).

(A) -2736 kJ
(B) -696 kJ
(C) 696 kJ
(D) 2736 kJ

37. For which process is DS° negative?

(A) the rusting of iron
(B) the mixing of two ideal gases
(C) the sublimation of carbon dioxide
(D) a partially soluble salt dissolving in water

38. Which experiment will yield DG°?

(A) measuring the temperature change when a known mass of sodium hydroxide solid is added to a known mass of distilled water.
(B) continually measuring the pH during the titration of a strong base of known concentration with a known volume of a weak acid of unknown concentration.
(C) measuring the volume of a known mass of oxygen at STP
(D) measuring the height of a plug of mercury above a sample of air in a capillary tube, at several temperatures.

39. A 20.0-liter vessel initially contains 0.50 mole each of H₂ and I₂ gases. These substances react and finally reach an equilibrium condition. Calculate the equilibrium condition of HI if K_eq = 49.

(A) 0.78 M
(B) 0.039 M
(C) 0.033 M
(D) 0.021 M

40. In the laboratory the equilibrium constant for a particular reaction can be measured at different temperatures. Plotting the data yields the graph shown below: Which of the following statements is false? (Note: The notation 4.40e-4 is equivalent to 4.40 x 10¯⁴.)

(A) DS° can be obtained from the y-intercept.
(B) The slope of the line is equal to -(DH°/R)
(C) The reaction is endothermic.
(D) The free energy of the reaction is positive.

41. 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

42. The following initial rate data were collected for the reaction:

aA(g) + bB(g) ---> cC(g) + dD(g);

The rate law that best fits this data is

(A) rate = k[A]¹[B]¹
(B) rate = k[A]¹[B]²
(C) rate = k[A]²[B]¹
(D) rate = k[A]²[B]⁰

43. If Experiment #1, in problem 42, is allowed to proceed further, it is found that after 5 days the concentrations of all the species are;

Which is the correct balanced chemical equation for the reaction?

(A) A(g) + B(g) ---> C(g) + D(g)
(B) 2 A(g) + B(g) ---> C(g) + 2 D(g)
(C) 2 A(g) + 2 B(g) ---> C(g) + 3 D(g)
(D) A(g) + 2 B(g) ---> C(g) + 3 D(g)

44. Which statement concerning the stratospheric ozone levels is false?

(A) The concentration of stratospheric ozone over Antarctica decreases in the summer and returns to normal levels during the winter.
(B) Chlorine radicals derived from chlorofluorocarbons have been implicated as causing the drop in ozone levels.
(C) The ozone layer is important because it absorbs high energy solar radiation which could cause damage to plants and animals.
(D) New research suggests that heterogeneous reactions may play a crucial role in changing the levels of ozone in the stratosphere.

45. A solution forms a precipitate upon addition of NaOH solution. When the precipitate is dissolved in HCl and treated with KCNS solution, a deep-red color is observed. The original solution probably contained the cation

(A) Fe²⁺
(B) Cr³⁺
(C) Fe³⁺
(D) Mn²⁺

46. A precipitate forms when HCl is added to an aqueous solution, but the precipitate dissolves when a small amount of hot water is added. The original solution probably contained the cation

(A) Ag⁺
(B) Pb²⁺
(C) Hg₂²⁺
(D) Hg²⁺

47. Al(OH)₃ is an insoluble solid whose K_sp = 1.9 x 10¯³³. What is the maximum concentration of OH¯ which can exist in 0.10 M AlCl₃ solution without causing Al(OH)₃ to precipitate?

(A) 2.7 x 10¯¹¹
(B) 1.4 x 10¯¹⁰
(C) 8.7 x 10¯⁸
(D) 3.1 x 10¯⁷

48. The compound CaO is

(A) an acid anhydride.
(B) a basic anhydride.
(C) an amphoteric oxide.
(D) an alkaline earth metal.

49. When H₂PO₄¯ behaves as a Bronsted base it becomes

(A) H₃PO₄
(B) HPO₄²¯
(C) HPO₃
(D) PO₄³¯

50. What is the solubility of MgF₂ in water at 25 °C if its K_sp is 6.4 x 10¯⁹?

(A) 6.4 x 10¯⁹
(B) 5.7 x 10¯⁵
(C) 1.9 x 10¯³
(D) 1.2 x 10¯³

51. Which salt will produce an acid solution when dissolved in water?

(A) NH₄Cl
(B) NaCN
(C) NH₄CN
(D) NaCl

52. What is the pH of a 1.0 x 10¯⁹ molar HCl solution?

(A) 5
(B) 6
(C) 7
(D) 9

53. Forty milliliters (40.00 mL) of 0.0900 M NaOH is diluted to 100.00 mL with distilled water and 30.00 mL of 0.1000 M HCl are added. The pH of the resulting solution is

(A) 9.57
(B) 11.66
(C) 12.18
(D) 12.38

54. Five acids are listed below in order of decreasing acid strength:

HCl > HC₂H₃O₂ > HCN > H₂O > NH₃.

For which of the following reactions must the numerical value of the equilibrium constant be less than one?

(A) HCl + H₂O <==> H₃O⁺ + Cl¯
(B) H₂O + NH₂¯ <==> NH₃ + OH¯
(C) HC₂H₃O₂ + OH¯ <==> C₂H₃O₂¯ + H₂O
(D) HCN + C₂H₃O₂¯ <==> HC₂H₃O₂ + CN¯

55. What is the pH at the equivalence point in a titration of 0.020 M NH₃(aq) with 0.020 M HBr(aq)? For ammonia, K_b = 1.8 x 10¯⁵.

(A) 5.5
(B) 5.6
(C) 7.0
(D) 8.5

56. A solution of a weak monoprotic acid is titrated with a 0.10 M strong base solution. Using a pH meter fitted with a glass and calomel electrode, a titration curve is constructed from pH values versus volume of base added. What information could NOT be obtained from the titration curve alone?

(A) the pK_a of the acid
(B) the molecular weight of the acid
(C) the millimoles of acid in the solution
(D) the best buffering region for the system

57. Which would make the best aqueous buffer solution?

(A) 0.10 M NH₄OH / 0.10 M NH₄Cl
(B) 0.10 M NH₄OH / 0.40 M NH₄Cl
(C) 0.10 M NH₄OH / 0.10 M HCl
(D) 0.10 M KOH / 0.10 M HCl

58. What must be the ratio of acetate ion concentration to acetic acid concentration in an aqueous solution in order to provide a solution of pH 5? The K_a of acetic acid is 1.8 x 10¯⁵.

(A) 0.056
(B) 1.0
(C) 1.8
(D) 5.0

59. The compound often used to provide a mild oxidizing condition in water for bleaching and for disinfecting is

(A) NaCl
(B) Ca(ClO)₂
(C) HF
(D) PbCr₂O₇

60. The highest oxidation number commonly observed for any ionic or molecular transition metal species is

(A) 2
(B) 3
(C) 6
(D) 7

61. In the electrolytic refining of copper, an electric current is passed through a cell containing a pure copper electrode, an electrode of impure copper, and an aqueous solution containing copper cations. As metallic copper is removed from the impure electrode and redeposited on the pure copper electrode other metallic impurities are left behind if the potential of the cell is adjusted properly. In this process, the impure copper electrode is called the

(A) anode.
(B) cathode.
(C) reference electrode.
(D) indicating electrode.

62. Given the standard electrode (reduction) potentials:

Which pair of substances will react spontaneously?

(A) Ni²⁺ with Cr³⁺
(B) Ni with Cr³⁺
(C) Ni²⁺ with Cr
(D) Ni with Cr

63. A certain solid-state ion-selective electrode responds according to the equation

E = constant + 0.0591 log(a_M²⁺)^1/2

where a_M²⁺ is the activity of a divalent cation M²⁺. The potential of the electrode was measured to be 0.2500 V when the electrode was immersed in a solution of Cu²⁺ with an activity, a_Cu²⁺, of 2.0 x 10¯⁴ M. The potential of the electrode in an unknown solution of Cu²⁺ was 0.2796 V. The activity of the Cu²⁺ in the unknown solution is

(A) 2.0 x 10¯³ M.
(B) 6.3 x 10¯⁴ M.
(C) 6.3 x 10¯⁴ M.
(D) 2.0 x 10¯⁴ M.

64. A mixed precipitate of NaCl and KCl weighing 0.2076 gram was dissolved and titrated with silver nitrate. The titration required 28.50 mL of 0.1055 M AgNO₃. What was the weight percent of NaCl in the mixed precipitate?

(A) 78.40%
(B) 71.00%
(C) 43.90%
(D) 29.00%

65. The most precise meausurement of an atomic or molecular weight on the ¹³C mass scale is by

(A) gravimetric carbon-hydrogen analysis.
(B) equivalent weight titration.
(C) gas density measurements.
(D) mass spectrometry.

66. Indifferent electrolytic solutions, that is solutions containing ions other than those involved in the analysis, are used to wash precipitates rather than distilled water because

(A) the wash solution must be able to conduct electrical current.
(B) precipitates are too insoluble in distilled water.
(C) the indifferent electrolytes prevent peptization (dispersion) of the precipitated salt.
(D) the precipitated solid must be kept in the colloidal state.

67. A sample of iron ore, weighing 0.700 gram, is dissolved in nitric acid. The solution is then diluted with water, following which sufficient concentrated aqueous ammonia is added to quantitatively precipitate the iron as Fe(OH)₃. The precipitate is filtered then ignited and weighed as Fe₂O₃. If the weight of the ignited and dried precipitate is 0.541 gram, what is the weight percent of iron in the original iron ore sample?

(A) 27.0%
(B) 48.1%
(C) 54.1%
(D) 81.1%

68. Any saturated hydrocarbon that is classified as an octane must have the molecular formula

(A) C₈H₈
(B) C₈H₁₄
(C) C₈H₁₆
(D) C₈H₁₈

69. The presence of a carbon-carbon double bond in an orbanic molecule

(A) results in a linkage between carbon atoms that has a much smaller bond energy that that of single carbon to carbon bonds.
(B) results in greater reactivity, often with addition of two atoms to the two carbon atoms of the bond.
(C) makes the molecule much more polar and therefore much more soluble in water.
(D) allows internal molecular rotations so that there are no isomers with the same formula possible.

70. Proteins that catalyze a metabolic reaction are

(A) metabolites.
(B) micelles.
(C) substrates.
(D) enzymes.