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U.S. National Chemistry Olympiad

1989 Local Section Test

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1. The periodic table contains an atomic weight for each of the elements. This atomic weight is

a. the arithmetic average of the masses of the naturally occurring isotopes of the elements.
b. The abundance-weighted average of the masses of the naturally occurring isotopes of the element
c. the mass of the most abundant isotopes of the element
d. the ratio of the mass of one atom of the element to the mass of one hydrogen atom

2. An atom, X, has a mass that is four times that of a carbon atom. What mass of X will combine with one gram of carbon in forming the compound X2C?

a. 1.00 grams
b. 2.00 grams
c. 4.00 grams
d. 8.00 grams

3. One mole of glucose, C6H12O6, contains

a. six moles of oxygen molecules.
b. six grams of hydrogen.
c. six atoms of carbon
d. 12 moles of hydrogen atoms.

4. The element M forms the forms the bromide MBr2. Analysis shows that this compound is 26.9 mass % M. The atomic weight of M is?

a. 29.4 g/mol.
b. 49.2 g/mol.
c. 58.8 g/mol.
d. 73.1 g/mol.

5. Aluminum reacts with oxygen to form Al2O3. Which pair of elements would most likely yield a compound with a similar formula?

a. In and S
b. B and F
c. Si and O
d. Zn and N

6. The charge of the nucleus of a calcium ion, Ca2+, in terms of the magnitude of charge of an electron, e, is

a. +20 e
b. +18 e
c. 0
d. -18 e

7. Under the proper conditions, calcium sulfate forms a hydrate. When a 3.50 grams sample of the hydrate is heated to constant mass, the residue remaining has a mass of 2.77 grams. The formula of the hydrate is

a. CaSO4 . H2O
b. CaSO4 . 2 H2O
c. CaSO4 . 5 H2O
d. CaSO4 . 8 H2O

8. Which set contains three isoelectronic species?

a. Cu, Ag, Au
b. Cl+, Ar, K
c. P3, Se2, I
d. H, Li+, Be2+

9. Which is the correct ground state electronic configuration for Mn2+?

a. [Ar]4s2 3d3
b. [Ar]4s2 3d5
c. [Ar]4s1 3d4
d. [Ar]4s0 3d5

10. The molecule ONCl has in its correct Lewis structure a total of

a. 2 bonding pairs of electrons and 7 lone pairs.
b. 3 bonding pairs of electrons and 6 lone pairs.
c. 4 bonding pairs of electrons and 5 lone pairs.
d. 5 bonding pairs of electrons and 4 lone pairs.

11. Which set would be properly classified as a collection of covalent molecules?

a. NaCl, Cl2, O2
b. CO2, NH4Cl, C2H6
c. AgCl, ScF3, P4
d. CO2, HCN, O2

12. For the representative elements, going from left to right across a period in the periodic table of the elements:

a. atomic size increases.
b. electronegativity decreases.
c. ionization energy becomes greater.
d. the outer electrons are held more weakly.

13. Which has the largest F-X-F angle?

a. NF3
b. BF3
c. CF4
d. SF6

14. The ability of an atom to compete for electrons with another atom to which it is bonded describes:

a. ionization potential
b. electronegativity
c. electron affinity
d. magnetism

15. Which set contains all linear molecules?

a. CO2, HCN, O2
b. BF3, Cl2, O2
c. H2S, CO, CO2
d. H2S, HCN, CO2

16. A hydrocarbon sample was burned completely in oxygen to produce 132 mg of carbon dioxide and 27.1 mg of water. The empirical formula for the hydrocarbon is

a. CH
b. CH2
c. CH3
d. C3H3

17. Find the empirical formula for a compound whose percent composition by mass is 49.4% K, 20.0% S, and 30.3% O.

a. KSO4
b. K2SO3
c. K2SO4
d. K4S2O3

18. Select the set of coefficients which will balance the chemical equation:

_B3N3H6 + _O2 ---> _N2O5 + _B2O3 + _H2O.

a. 1, 5, 1, 1, 2
b. 1, 15, 3, 3, 6
c. 2, 5, 3, 3, 3
d. 2, 15, 3, 3, 6

19. 1.40 kg of potassium chlorate is heated to produce oxygen has according to the balanced chemical equation

2 KClO3 --->2 KCl + 3 O2.

The quantity of oxygen that can be produced is

a. 182 g.
b. 364 g.
c. 546 g.
d. 1.09 kg.

20. Given the reaction

Pb(NO3)2 (aq) + 2 KI (aq) ---> PbI2 (s) + 2 KNO3 (aq),

what mass of lead(II) iodide will precipitate if 10.2 g of lead (II) nitrate is mixed with 5.73 g of potassium iodide in a sufficient quantity of water?

a. 2.06 g
b. 4.13 g
c. 7.96 g
d. 15.9 g

21. Three liters of sulfur dioxide gas, SO2, and two liters of oxygen has, O2, are reacted at a certain temperature and pressure. How many liters of gaseous sulfur trioxide, SO3, can be produced at that same temperature and pressure?

a. 1.0 liter
b. 1.5 liters
c. 2.0 liters
d. 3.0 liters

22. Gases tend to exhibit non-ideal behavior under conditions of

a. low temperature and low pressure.
b. low temperature and high pressure.
c. high temperature and high pressure.
d. any temperatures far above the critical point.

23. The density of argon gas at 100C and 2.5 atm. is

a. 4.3 x 103 g/liter.
b. 2.5 x 102 g/liter.
c. 3.3 g/liter.
d. 4.5 g/liter.

24. According to the simple kinetic molecular theory,

a. the absolute temperature of a gas depends on its molecular weight.
b. the pressure exerted on a gas affects the speed of its molecules.
c. gaseous molecules are continuously in random motion and collisions are perfectly elastic.
d. gaseous molecules travels in curved paths.

25. Uranium hexafluoride is a gas used to effect the separation of the 235U isotope from 238U. The relative rate of effusion, that is the ratio of the rate of effusion of the 235U compound to the rate of the 238U compound, is

a. 0.9940
b. 1.004
c. 1.006
d. 1.008

26. The miscibility of water and ethyl alcohol is chiefly due to intermolecular forces known as

a. covalent bonds.
b. dispersion forces.
c. hydrogen bonds.
d. ion-ion attractions.

27. How many grams of AgNO3 are needed to prepare 500 mL of a 0.240 M solution?

a. 1.42 g
b. 20.4 g
c. 120 g
d. 354 g

28. Which best explains why bromine is soluble in carbon tetrachloride?

a. Both substances are liquids.
b. Both substances have densities that are nearly equal.
c. Both substances are made up of nonpolar molecules.
d. Both Br and Cl have high electronegativities.

29. Which gas is most soluble in water?

a. CO2
b. CH4
c. O2
d. NH3

30. A solution is known to contain Ca2+ ions and Pb2+ ions. What will happen when 3 M HCl is added to the solution?

a. Only CaCl2 will precipitate.
b. Only PbCl2 will precipitate.
c. CaCl2 and PbCl2 will both precipitate.
d. No precipitate will form.

31. Which compound is insoluble in water?

a. BaSO4
b. CuCl2
c. (NH4)2S
d. Pb(NO3)2

32. A saturated solution of Ca(OH)2 in water at 25 C is 0.011 mol/L Ca(OH)2. The solubility product constant of Ca(OH)2 at 25 C is

a. 1.3 x 106
b. 5.3 x 106
c. 1.2 x 104
d. 2.4 x 104

33. Magnesium oxalate ionizes by the reaction

MgC2O4 (s) <===> Mg2+ (aq) + C2O42 (aq) The Ksp = 8.6 x 105. What will occur when 200 mL of 0.0010 M Mg(NO3)2 is mixed with 300 mL of 0.0020 M Na2C2O4?

a. A precipitate of MgC2O4 and of NaNO3 will form.
b. A precipitate of NaNO3 only will form.
c. A precipitate of MgC2O4 only will form.
d. The solutions will mix to form a clear solution.

34. Although the compound lead carbonate, PbCO3, is nearly insoluble in water, it dissolves more readily in a solution of 0.1 M HBr because

a. HBr is a weak acid.
b. H2CO3 is a weak acid.
c. all salts are soluble in acids.
d. PbCO3 is an ionic salt.

35. What quantity of heat is needed to convert 0.0500 mole of liquid benzene at 20 C to the vapor at 130 C? For benzene: melting point = 5 C, boiling point = 80 C; heat capacity : solid, 75.3 J/mol-K; liquid, 142 J/mol-K; gas, 92.0 J/mol-K; DH(fusion) = 10.0 kJ/mol, DH(vaporization) = 31.0 kJ/mol.

a. 0.113 kJ
b. 2.21 kJ
c. 7.10 kJ
d. 29.7 kJ

36. When 50 g of an aqueous solution that contains 0.050 mole of HCl and 50 g of an aqueous solution that contains 0.050 mole of NaOH are mixed in a calorimeter, the temperature of the resulting solution rises from 21.0 C to 27.5 C. Assuming the heat capacity of the solution is close to that of pure water (4.184 J/deg/g) and that the heat capacity of the calorimeter can be ignored, the standard heat of reaction for HCl(aq) + NaOH (aq) ---> H2O(l) + NaCl(aq) is

a. - 54 kJ/mol
b. - 27 kJ/mol
c. -10.8 kJ/mol
d. -2.7 kJ/mol

37. Which substance has the largest standard molar entropy at 25 C?

a. He(g)
b. H2(g)
c. Na(s)
d. CH4(g)

38. If the reacting system

PCl3 (g) + Cl2 (g) <===> PCl5 (g), DH = - 92.6 kJ,

is held at constant volume, the concentration of Cl2 will increase if

a. PCl3 is added to the system.
b. PCl5 is added to the system.
c. the temperature of the system is lowered.
d. an inert gas is added to the system.

39. Which is the correct equilibrium expression for the reaction N2O4 (g) <===> 2 NO2(g)?

a. Kc = [NO2] / [N2O4]
b. Kc = [N2O4] / [NO2]
c. Kc = [NO2]2 / [N2O4]
d. Kc = 2 [NO2] / [N2O4]

40. Consider the equilibrium

CaCO3 (s) <===> CaO (s) + CO2 (g)

in a closed container at a certain temperature. The easiest way to measure the equilibrium constant for the system is to measure

a. the DG of the reaction.
b. the pressure of the CO2 gas.
c. the molar concentrations of all the reactants.
d. the forward and reverse rate constants.

41. A mixture of 0.500 mole of H2 and 0.500 mole of I2 was placed in a 1.00 liter apparatus at 430 C and was allowed to come to equilibrium with the formation of HI according to the equation

H2 (g) + I2 (g) <===> 2 HI (g).

If the equilibrium constant at this temperature is Kc = 54.3, what is the molar concentration of H2 (g) in the equilibrium mixture?

a. 0.107 mol/L
b. 0.500 mol/L
c. 1.20 mol/L
d. 2.00 mol/L

42. A catalyst

a. reacts to form a product.
b. changes the equilibrium concentrations of products.
c. works like a buffer.
d. acts by altering the energy barriers of intermediate steps in a reaction.

43. The half-life of a radioactive isotope of mercury is 31 days. What mass of a 0.100 gram sample of this isotope will remain after 125 days have elapsed?

a. 0.00625 g
b. 0.0125 g
c. 0.0250 g
d. 0.000 g

44. Which oxide is the most acidic?

a. CaO
b. SO3
c. P2O5
d. BeO

45. The conjugate base of HPO42 is

a. H3PO4
b. H2PO4
c. Na2PO4
d. PO43

46. Which is not an acid-base reaction?

a. NaOH + HCl -> NaCl + H2O
b. SO2 + H2O -> H2SO3
c. HCl + Zn --> ZnCl2 + H2
d. K2O + H2O --> 2 KOH

47. What is the pH of a solution that is 4.0 x 104 M HBr?

a. 1.73
b. 3.40
c. 7.00
d. 10.60

48. Which is the most powerful oxidizing agent?

a. iodine
b. sodium
c. chlorine
d. SO2

49. Zinc reacts with dilute acid to produce H2 and Zn2+ but silver does not liberate hydrogen from an acid. This information enables one to predict that

a. H2(g) + Zn2+(aq) --> 2H+(aq) + Zn(s)
b. 2 Ag(s) + Zn2+(aq) --> 2Ag+(aq) + Zn(s)
c. 2 Ag+(aq) + Zn(s) --> 2Ag(s) + Zn2+(aq)
d. 2 Ag(s) + 2H+(aq) --> H2(g) + 2 Ag+(aq)

50. In the electroplating of silver from cyanide solution the cathode reaction is

Ag(CN)2 (aq) + e- --> Ag(s) + 2CN (aq)

How many grams of silver should be deposited by a current of 4.50 amperes in 28.0 minutes?

a. 0.141 g
b. 4.23 g
c. 8.45 g
d. 12.53 g

51. An alloy of aluminum and copper is analyzed for percentage composition. A 0.2052 g sample of the alloy is dissolved in sulfuric acid (copper does not react with sulfuric acid) and 229.5 mL of hydrogen gas are collected at 700 torr and 29 degrees C. The balanced equation is

2 Al + 3H2SO4 ---> Al2(SO4)3 + 3 H2.

The percentage of aluminum in the alloy is

a. 25.23 %
b. 37.38 %
c. 50.48 %
d. 74.76 %

52. Commercial sulfuric acid has a density of 1.84 g/mL and is 96.0 % H2SO4 by weight. If 25.0 mL of this concentrated acid is diluted to 500 mL with water, what is the molarity of the final solution?

a. 0.450 M
b. 0.900 M
c. 0.938 M
d. 1.80 M

53. Blood hemoglobin contains approximately 0.33% iron, by weight. How many iron atoms are present in each hemoglobin molecule if the molecular weight of hemoglobin is about 68,000 grams per mole?

a. 1
b. 2
c. 3
d. 4

54. Cu(II) ions will react with excess I to liberate I2:

2 Cu2+ + 2 I ---> 2 Cu2+ + I2

The liberated iodine is titrated with standard Na2S2O3 solution:

I2 + 2 S2O32 ---> 2 I + S4O62

A 0.2129 g sample of a copper ore required 28.42 mL of 0.04411 M sodium thiosulfate to titrate the liberated I2. What is the percentage of copper in the ore?

a. 13.56 %
b. 18.70 %
c. 37.41 %
d. 74.82 %

55. Propionic acid (pKa = 5) is titrated with a sodium hydroxide solution. In order to most accurately determine the endpoint of the titration, which indicator would be the best choice?

a. methy1 violet, pH range: 0 - 2
b. bromcresol green, pH range: 4.0 - 5.6
c. phenolphthalein, pH range: 8.3 - 10.0
d. trinitrobenzene, pH range: 12.0 - 14.3

56. The pH of a 5 x 108 M HCl solution is

a. 6.89
b. 7.00
c. 7.30
d. 8.50

57. A 0.0610 g sample of a brominated organic compound is combusted in an atmosphere of oxygen and the bromine reduced to bromide ion with hydroxylamine sulfate. The resulting bromide solution is titrated with 0.0095 M AgNO3 and requires 8.37 mL to reach the equivalence point. The percentage of bromine in the sample is

a. 5.20%
b. 8.35%
c. 10.4%
d. 20.8%

58. Given the standard electrode potentials:

Cu2+(aq) + 2e ---> Cu(s) E = 0.337V
Al3+(aq) + 3e ---> Al(s) E = -1.66V

The voltage of the cell Cu | CuSO4(0.5M) || Al2(SO4)3(0.1M) | Al would be

a. 0.00 V
b. 0.72 V
c. 2.01 V
d. 5.70 V

59. For the reversible reaction

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

the rate of the forward reaction is much larger than the rate of the reverse reaction when

a. there is an excess of NH3 and little N2 and H2.
b. the reaction is at equilibrium.
c. NH3 is present but no H2 and N2 are present.
d. N2 and H2 but no NH3 are present.

60. In the reaction, 2X + Y = 2R, all the substances are in the gaseous state. When this system is in equilibrium, a 5.00 liter container contains 2.00 moles of X, 1.00 mole of Y and 4.00 moles of R. The value of the equilibrium constant, Kc, is

a. 20.00
b. 4.00
c. 2.00
d. 1.00

61. In which process is entropy decreased?

a. heating water.
b. evaporating a beaker of ethanol.
c. subliming solid iodine.
d. condensing bromine vapor.

62. Which compound is a strong electrolyte in aqueous solution?

a. HNO3
b. NH3
c. CH3COOH
d. C2H5OH

63. The solubility product constant of AgCl is

a. the same in water as it is in 0.2 M AgNO3.
b. greater in water than it is in 0.2 M AgNO3.
c. less in water than it is in 0.2 M AgNO3.
d. less in 0.2 M NaCl than it is in 0.2 M AgNO3.

64. The heat of formation of ethyl alcohol, C2H5OH, cannot be measured directly. Calculate this heat of formation from the following heats of combustion:

C(s) + O2(g) ---> CO2(g) DH = - 393 kJ
H2(g) + 1/2 O2(g) ---> H2O(g) DH = - 286 kJ
C2H5OH(l) + 3O2(g) ---> 2CO2(g) + 3H2O(g) DH = - 1370 kJ

a. - 2061 kJ/mol
b. - 1298 kJ/mol
c. - 274 kJ/mol
d. + 691 kJ/mol

65. The reaction between H2 and NO was found to be described by the rate equation

rate = k[H2][NO]2

Therefore,

a. the balanced chemical equation for the reaction is H2 + 2 NO ---> products.
b. the rate-determining step must be a three-body collision.
c. the reaction is second order.
d. the reaction is third order.

66. Twelve is the coordination number of

a. an atom in a hexagonal close-packed metallic solid.
b. a metal atom in a body-centered-cubic structure.
c. a metal atom in a simple cubic structure.
d. a Na+ ion in a NaCl crystal.

67. The molal boling point elevation constant for benzene in 2.53 C/m The boiling point of pure benzene is 80 C. What is the boiling point of a solution of 5.00 g of naphthalene, C10H8, in 100 g of benzene?

a. 81 C
b. 79 C
c. 75 C
d. 0.99 C

68. Which would you classify as a semiconductor?

a. diamond
b. silicon
c. lead
d. MgBr2

69. Lactic acid, CH3CHOHCOOH, gets its name from sour milk (Latin - lactis), from which it was first isolated in 1780. Ka = 8.4 x 104. What is the pH of a sample of sour milk containing 0.50 M lactic acid?

a. 1.4
b. 1.7
c. 3.4
d. 3.7

70. Elemental analysis of a hydrocarbon sample requires complete combustion of the sample. The analysis of the combustion products relies upon the assumption that

a. the quantity of water formed is limited by the amount of air present.
b. the quantity of water formed is limited by the amount of oxygen present in the sample.
c. the quantity of carbon dioxide formed is limited by the amount of air present.
d. the quantity of carbon dioxide formed is limited by the amount of carbon present in the sample.