U.S. National Chemistry Olympiad

1991 Local Section Test


1. What is the maximum amount of MgCl2 that can be prepared from the reaction of 10.0g of HCl with 10.0 of Mg(OH)2 ?

2 HCl + Mg(OH)2 ---> MgCl2 + 2 H2O

(A) 9.26 g
(B) 13.1 g
(C) 16.3 g
(D) 17.5 g

2. Phenylflouroform contains 57.54% C, 3.45% H, and 39.01% F. Its molecular formula is the same as its simplest formula. How many carbon atoms are in one molecule of Phenyflouroform ?

(A) 4
(B) 5
(C) 6
(D) 7

3. What is the most likely formula for a compound of gallium and sulfur ?

(A) GaS
(B) GaS2
(C) Ga2S3
(D) Ga3S2

4. A mixture of 2.30 x 1023 molecules N2 and 4.35 x 1023 molecules N2O has a total pressure of 2.00 atm. What is the partial pressure of N2 ?

(A) 0.346 atm
(B) 0.654 atm
(C) 0.692 atm
(D) 1.11 atm

5. Which element should have the smallest first ionization energy ?

(A) Ca
(B) Rb
(C) Al
(D) Cl

6. An aqueous solution containing 1.00 mol H2SO4 is mixed with an aqueous solution containing 1.00 mol NaOH. The mixture is then evaporated to dryness. What solid remains after evaporation ?

(A) H2SO4
(B) NaOH
(C) NaHSO4
(D) Na2SO4

7. Which atom is the smallest ?

(A) Rb
(B) Ag
(C) Sb
(D) I

8. At room temperature and 1 atm pressure the molecules are farthest apart in

(A) flourine
(B) bromine
(C) iodine
(D) water

9. What is the net-ionic equation for the reaction of aqueous solutions of BaCl2 and K2SO4?

(A) Ba2+(aq) + 2Cl¯(aq) + 2K+(aq) + SO42¯(aq) ---> BaSO4(s) + 2K+(aq) + 2Cl¯(aq)
(B) Ba2+(aq) + SO42¯(aq) ---> BaSO4(s)
(C) K+(aq) + Cl¯(aq) ---> KCl(s)
(D) Ba2+(aq) + 2Cl¯(aq) + 2K+(aq) + SO42¯(aq) ---> BaSO4(s) + 2KCl(s)

10. When 80.00 mL of 0.200 M HNO3 is added to 120.00 mL of 0.150 M KOH, the reaction

HNO3(aq) + KOH(aq) ---> KNO3(aq) + H2O(l)

occurs and the resulting solution is

(A) 0.0160 M KNO3
(B) 0.0180 M KNO3
(C) 0.0800 M KNO3 and 0.0100 M KOH
(D) 0.0160 M KNO3 and 0.0200 M KOH

11. Methanol burns in oxygen according to the equation

CH3OH + O2 ---> CO2 + H2O (unbalanced)

What volume of oxygen is required to burn 5.0 L of gaseous methonal measured at the same temperature and pressure ?

(A) 15.0 L
(B) 3.3 L
(C) 7.5 L
(D) 5.0 L

12. A 50 g sample of an ideal gas occupies a volume of 3.2 L at 40 °C and exerts a pressure of 2.6 atm. What is its molar mass ?

(A) 150 g mol¯1
(B) 2.0 g mol¯1
(C) 77 g mol¯1
(D) 310 g mol¯1

13. When sodium metal reacts with an excess of water the products are

(A) Na2O(s) and H2(g)
(B) Na+(aq), OH¯(aq) and H2(g)
(C) NaH(s) and O2(g)
(D) Na2O2(s) and H2(g)

14. Which is least important in determining the physical behavior of a gas?

(A) volume
(B) pressure
(C) temperature
(D) chemical composition

15. Which pair of atoms should form the most polar bond ?

(A) B and F
(B) C and O
(C) O and F
(D) F and N

16. Which pair of ions should form the strongest ionic bond?

(A) Li+ and I¯
(B) Na+ and F¯
(C) Cs+ and F¯
(D) Na+ and O2¯

17. The kinetic-molecular theory predicts that two gases at the same temperature will have the same

(A) average speed
(B) average kinetic energy
(C) pressure
(D) rate of effusion

18. Which factors do not affect the vapor pressure of a liquid at equilibrium?

I. Intermolecular forces of attraction.
II. The volume of liquid present.
III. The temperature of the liquid

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

19. Which has the highest vapor pressure at room temperature ?

(A) a vegetable oil
(B) gasoline
(C) table sugar, C12H22O11
(D) table salt, NaCl

20. Identify the best Lewis structure for hydrogen cyanide.

21. Which oxide of chlorine exhibits the maximum oxidation state that really exists for chlorine?

(A) ClO
(B) ClO4
(C) Cl2O5
(D) Cl2O7

22. Which has the largest radius ?

(A) Na
(B) Na+
(C) F¯
(D) Ne

23. What is the molarity of HCl if 450 mL of 2.3 M HCl is diluted to 1250 mL ?

(A) 0.36 M
(B) 0.50 M
(C) 0.83 M
(D) 1.8 M

24. The first five ionization energies in kJ mol¯1, for a particular element are shown.

1st 2nd 3rd 4th 5th
580 1815 2740 11,600 18,500

The element is likely to form a ionic compounds in which its charge is

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

25. Which compound, when dissolved in water, conducts electricity and forms a basic solution ?

(A) HCl

26. Which pair constitutes a buffer ?

(A) HCl and KCl
(B) NaOH and NaCl
(C) HNO2 and NaNO2
(D) HNO3 and NH4NO3

27. Which oxide dissolves in water to give the strongest acid ?

(A) SO3
(B) CaO
(C) P4O10
(D) CO2

28. Which is the strongest Bronsted base ?

(A) NH2¯
(B) Cl¯
(C) PO43¯
(D) NO2¯

29. In the reaction F¯ + H2O ---> HF + OH¯ an acid-base conjugate pair is

(A) F¯ and H2O
(B) F¯ and OH¯
(C) H2O and HF
(D) F¯ and HF

30. Which is the anhydride of nitric acid ?

(A) NO
(B) NO2
(C) N2O3
(D) N2O5

31. Which forms a basic aqeous solution ?

(A) NaI
(B) KNO3
(C) BaCl2
(D) Na2CO3

32. The best acid for preparing a buffer of pH = 3.2 has a Ka near

(A) 2.0 x 10¯5
(B) 6.0 x 10¯4
(C) 3.2 x 10¯2
(D) 4.0 x 10¯6

33. What is the pH of a 2.0 x 10¯3 M HCl solution ?

(A) 2.40
(B) 2.70
(C) 3.00
(D) 11.30

34. Consider a solution that contains only one ion, Ag+, Pb2+, or Hg22+. The solution gave a precipitate with HCl that was insoluble in hot water but was soluble in dilute ammonia solution. Which ion was present ?

(A) Pb2+
(B) Ag+
(C) Hg22+
(D) The information is insufficient to identify the ion

35. What is the partial pressure of CO2(g) if Kp for the reaction is 1.04 atm ?

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

(A) 0.52 atm
(B) 1.04 atm
(C) 1.08 atm
(D) 10.4 atm

36. The Ksp values for CaSO4,BaSO4, and Ag2SO4 are 2.0 x 10¯4, 1.5 x 10¯9, and 1.5 x 10¯5 respectively. If 0.010 M Na2SO4 is slowly added to a solution that contains Ca2+, Ba2+, and Ag+ (each 0.10M), which solid will precipitate last?

(A) CaSO4
(B) Ag2SO4
(C) BaSO4
(D) More information is required

37. The Ksp of AgCl is 1.8 x 10¯10. If 10.00 mL of 0.0010 M NaCl is combined with 20.00 mL of 0.0050 M AgNO3

(A) no reaction occurs
(B) a precipitate forms
(C) an initial precipitate forms which dissolves upon stirring.
(D) the silver ion concentration remainsas 0.005 M.

38. N2(g) + 3H2(g) <===> 2NH3(g) + 92.2 kJ

The partial pressure of N2 is not increased by

(A) decreasing container size
(B) adding NH3
(C) increasing temperature
(D) removing H2

39. Which value for an equilibrium constant, K, could indicate that the reaction

A(g) + B(g) ---> C(g)

goes nearly to completion?

(A) 1014
(B) 10¯14
(C) 1
(D) 0

40. Which is most soluble in a polar solvent?

(A) CF4
(B) Br2
(C) HCl
(D) BCl3

41. When a liquid is placed in a closed container

(A) evaporation stops
(B) evaporation continues for a time then stops
(C) the vapor pressure above the liquid becomes one atmosphere
(D) evaporation and condensation continue to occur, but at equal rates

42. The sublimination of dry ice is an endothermic process. The energy absorbed is required to overcome

(A) covalent bonds
(B) polar covalent bonds
(C) dipole forces
(D) dispersion forces

43. Compared to a 1.0 M aqueous solution of a nonelectrolyte, a 1.0 M solution of an electrolyte will have a

(A) higher melting point and higher boiling point
(B) higher melting point and lower boiling point
(C) lower melting point and lower boiling point
(D) lower melting point and higher boiling point

44. Which is planar?

(A) H3O+
(B) PCl3
(C) CO32¯
(D) NH4+

45. Calculate ΔH°f for

4 NH3(g) + 3 O2(g) ---> 2 N2(g) + 6 H2O(g)

Given that ΔH°f for NH3(g) and H2O(g) are -46.0 and -242 kJ mol¯1 respectively.

(A) -1268 kJ
(B) -196 kJ
(C) +1268 kJ
(D) +196 kJ

46. A white, odorless, crystalline solid melts after about ten seconds in a burner flame. It is soluble in water and insoluble in carbon tetrachloride. Neither the melt nor its aqueous solution conducts electricity. We conclude that the substance is

(A) an ionic compound
(B) a non-polar covalent compound
(C) a polar covalent compound
(D) a pure element

47. Given the standard reduction potentials,

Cr3+ + 3e¯ ---> Cr -0.74 V
Pb2+ + 2e¯ ---> Pb -0.13 V

what is the standard potential, E°, for the following reaction?

2 Cr + 3 Pb2+ ---> 2 Cr3+ + 3 Pb

(A) 0.61 V
(B) 0.87 V
(C) 1.09 V
(D) 1.87 V

48. A mixture of 0.10 mol H2 and 0.050 mol O2 are placed in a bomb calorimeter with a heat capacity of 5.1 x 104 J °C¯1. The initial temperature is 25.00 °C and the temperature after combustion is 25.56 °C. What is the ΔH°f for H2O(l)? (Assume 100% conversion to water.)

(A) -286 kJ mol¯1
(B) +190 kJ mol¯1
(C) -190 kJ mol¯1
(D) +286 kJ mol¯1

49. In the reaction

2MnO4¯ + 16H+ + 10Br¯ ---> 2Mn2+ + 8H2O + 5Br2

Br¯ ion is the

(A) oxidizing agent and is oxidized
(B) oxidizing agent and is reduced
(C) reducing agent and is oxidized
(D) reducing agent and is reduced

50. For BrF3, the orbital geometry of the central atom and the molecular geometry are, respectively,

(A) trigonal planar and trigonal planar
(B) trigonal planar and trigonal bipyramidal
(C) trigonal bipyramidal and trigonal planar
(D) trigonal bipyramidal and T-shaped

51. How many electrons are needed to convert one nitrate ion into one ammonia molecule?

(A) 3
(B) 5
(C) 6
(D) 8

52. Which species below violates the octet rule?

(A) CF4
(B) BF3
(C) N2O
(D) NO3¯

53. What is the coefficient for H2O when the redox equation

Cu + NO3¯ + H+ ---> Cu2+ + NO + H2O

is balanced using smallest whole - number coefficients?

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

54. Which change will produce an increase in the entropy of a system?

(A) decreasing the temperature
(B) forming a precipitate in a solution
(C) decreasing the volume
(D) forming a gas from a solid reaction

55. Which will cause the value of the equilibrium constant for this reaction to increase?

2A(g) + B(g) ---> C(g); ΔH° = 280 kJ

(A) adding a catalyst
(B) increasing the concentration of A
(C) increasing the concentration of C
(D) increasing the temperature

56. Given

2CO(g) + O2(g) ---> 2CO2(g); ΔG° = -516 kJ

4MnO(s) + O2(g) ---> 2Mn2O3(s); ΔG° = -312 kJ

Calculate the value of ΔG° for

2MnO(s) + CO2(g) ---> Mn2O3(s) + CO(g)

(A) +102 kJ
(B) -102 kJ
(C) +204 kJ
(D) -204 kJ

57. Given

Br2(l) S° = 152.2 J mol¯11 and ΔH°f = 0 kJ mol¯1
Br2(g) S° = 245.4 J mol¯11 and ΔH°f = 30.9 kJ mol¯1

Calculate the boiling point of liquid bromine.

(A) 58.4 K
(B) 332 K
(C) 125 K
(D) -147 K

58. Which is not expected to have a value of zero?

(A) ΔH°f for Cl2(g)
(B) ΔG°f for Na(s)
(C) S° for Ca(s)
(D) ΔH°f for Al(s)

59. The half-life of 14C is 5570 years. How many years will it take for 90% of a sample to decompose?

(A) 5,570 years
(B) 17,700 years
(C) 18,600 years
(D) 50,100 years

60. A solution containg 2.10 g of Fe(NH4)2(SO4)2 . 6 H2O (M = 392.1 g mol¯1) was titrated with acidic Na2Cr2O7 solution, requiring 41.60 mL of Na2Cr2O7 solution. What is the molarity of Na2Cr2O7?

6 Fe2+ + Cr2O72¯ + 14 H+ ---> 6 Fe3+ + 2 Cr3+ + 7 H2O

(A) 0.0215 M
(B) 0.0387 M
(C) 0.0644 M
(D) 0.0744 M

61. What is the approximate H-O-H bond angle in H3O+?

(A) 60
(B) 90
(C) 109
(D) 120

62. What hybrid orbitals are used by nitrogen in N2F2?

(A) sp
(B) sp2
(C) sp3
(D) p only

63. The strongest interaction between atoms listed below is

(A) an instantaneous dipole-dipole interaction
(B) a dipole-dipole interaction
(C) a hydrogen bond
(D) a covalent bond

64. When a 5.0 g sample of an unknown compound is dissolved in 250.0 g of benzene, the freezing point of benzene decreased 1.4 °C. The freezing point depression constant, Kf, for benzene is 5.12 °C m¯1. What is the approximate molar mass of the compound?

(A) 290 g mol¯1
(B) 73 g mol¯1
(C) 36 g mol¯1
(D) 140 g mol¯1


Half-cell reaction Standard reduction potential, E°
Cu2+ (aq) + 2e¯ ---> Cu(s) -0.25 V
Ni2+ (aq) + 2e¯ ---> Ni(s) +0.34 V

When two half-cells are connected using a salt bridge,

(A) a galvanic cell will result in which Cu is the cathode
(B) a galvanic cell will result in which Cu is the anode
(C) an electrolytic cell will result in which Ni is the anode
(D) an electrolytic cell will result in which Ni is the anode

66. What is the maximum number of electrons that can occupy the 5d subshell?

(A) 2
(B) 6
(C) 10
(D) 14

67. For the isoelectronic series below, which species requires the least energy to remove an outer electron?

(A) K+
(B) Ar
(C) Cl¯
(D) S2¯

68. In aqueous solution, iodide ion (in basic solution) is oxidized by hypochlorite ion:

OCl¯(aq) + I¯(aq) ---> OI¯(aq) + Cl¯(aq)

The rate of formation of hypoiodite, OI¯, is given by the rate law

rate = ( k [OCl¯] [I¯] ) / [OH¯]

What is the overall reaction order for the formation of OI¯?

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

69. The dissociation of HI molecules, as shown below, occurs at a temperature of 629 K. The rate constant, k = 3.02 x 10¯511.

2 HI(g) ---> H2(g) + I2(g)

What is the reaction order?

(A) 0
(B) 1
(C) 2
(D) 3

70. A sodium vapor street lamp emits yellow light with a wavelength of 589 nm. What is the energy of this light per mole of protons?

(A) 3.37 x 10¯16 kJ mol¯1
(B) 2.35 x 10¯13 kJ mol¯1
(C) 0.201 kJ mol¯1
(D) 203 kJ mol¯1