U.S. National Chemistry Olympiad: 1998 Local Section Test

Go to the answers

1. Which gas is most soluble in water?

(A) ammonia
(B) hydrogen
(C) methane
(D) nitrogen

2. For which family of elements does the melting point increase with increasing atomic mass?

1. alkali metals
2. halogens

(A) 1 only
(B) 2 only
(C) both 1 and 2
(D) neither 1 nor 2

3. Which pair of substances could be separated by a simple distillation in a school laboratory?

(A) ammonia and argon
(B) salt and water
(C) oil and vinegar
(D) flour and sugar

4. Which compound is least soluble in water?

(A) Al(NO₃)₃
(B) Na₃PO₄
(C) K₂SO₄
(D) PbCl₂

5. An object is dried by heating it in an oven. Which procedure would give the most accurate determination of its mass?

(A) The object is weighed while it is still warm.
(B) The object is weighed after being cooled on the laboratory bench.
(C) The object is weighed after being cooled in a desiccator.
(D) The object is weighed after being cooled by blowing air on it.

6. A sample of gas is to be identified by means of its behavior in the presence of a glowing splint. Which gas will neither itself burn nor cause the splint to burn?

(A) oxygen
(B) nitrogen
(C) hydrogen
(D) methane

7. A compound prepared as a model of hemoglobin is 4.6% iron by mass. If the compound is known to contain a single iron atom, which of these values will be closest to its molar mass?

(A) 1000 g mol¯¹
(B) 1200 g mol¯¹
(C) 1400 g mol¯¹
(D) 1600 g mol¯¹

8. How many hydrogen atoms are present in 0.046g of ethanol, C₂H₅OH? (Molar Mass of C₂H₅OH is 46 g mol¯¹)

(A) 6.0 x 10²⁰
(B) 1.2 x 10²¹
(C) 3.0 x 10²¹
(D) 3.6 x 10²¹

9. Which of these hydrated salts contains the greatest percentage of water by mass?

(A) BaCl₂ · 2H₂O
(B) CuSO₄ · 5H₂O
(C) CaCl₂ · 6H₂O
(D) Ni(ClO₄)₂ · 6H₂O

10. Ammonium dichromate, (NH₄)₂Cr₂O₇, decomposes when heated to produce N₂, H₂O, and Cr₂O₃ as represented by this equation.

__(NH₄)₂Cr₂O₇(s) ---> __N₂(g) + __H₂O(g) + __Cr₂O₃(s)

What is the coefficient for H₂O when this equation is correctly balanced using the smallest set of whole number coefficients?

(A) 1
(B) 2
(C) 4
(D) 8

11. What volume of 0.15 M HCl can be made from 7.5 mL of concentrated HCl (12M)?

(A) 0.060 L
(B) 0.60 L
(C) 6.0 L
(D) 6.0 x 10² L

12. Hematite, Fe₂O₃, is the most common iron ore. How many moles of hematite are in an ore sample that contains 355 g of iron? Assume hematite is the only source of iron in this ore.

(A) 1.11 mol
(B) 1059 mol
(C) 3.18 mol
(D) 6.36 mol

13. How many moles of Mg(OH)₂ can be precipitated when 15 mL of 0.20 M MgCl₂ solution is mixed with 25 mL of 0.18 M KOH?

(A) 0.0015 mol
(B) 0.0022 mol
(C) 0.0030 mol
(D) 0.0045 mol

14. A 2.0 mL sample of HCl(g) is mixed with a 1.5 mL of NH₃(g). What is the volume if the resulting mixture after the reaction is complete? (Assume all measurements are carried out at the same pressure and temperature and that the volume of the solid is negligible)

HCl(g) + NH₃(g) ---> NH₄Cl(s)

(A) 0.5 mL
(B) 1.5 mL
(C) 2.0 mL
(D) 3.5 mL

15. A student wants to prepare 250. mL of 0.10 M NaCl solution. Which procedure is most appropriate? (The molar mass of NaCl is 58.4 g mol¯¹)

(A) Add 5.84 g of NaCl to 250. mL of H₂O
(B) Add 1.46 g of NaCl to 250. mL of H₂O
(C) Dissolve 5.84 g of NaCl in 50 mL of H₂O and dilute to 250. mL.
(D) Dissolve 1.46 g of NaCl in 50 mL of H₂O and dilute to 250. mL.

16. Which set of temperature and pressure conditions will cause a gas to exhibit the greatest deviation from ideal gas behavior?

(A) 100 °C and 4 atm
(B) 100 °C and 2 atm
(C) -100 °C and 4 atm
(D) 0 °C and 2 atm

17. A mixture of 0.5 mol of CH₄, 0.5 mol of H₂ and 0.5 mole of SO₂ is introduced into a 10.0 L container at 25 °C. If the container has a pinhole leak, which describes the relationship between the partial pressures of the individual components in the container after 3 hours?

(A) P_SO2 > P_CH4 > P_H2
(B) P_SO2 < P_CH4 < P_H2
(C) P_SO2 < P_CH4 > P_H2
(D) P_SO2 = P_CH4 = P_H2

18. Which factor affects the vapor pressure of a liquid?

(A) Temperature
(B) atmosphereic pressure
(C) Volume of the liquid
(D) surface area of the liquid

19. A 500 mL gas sample is collected over water at a pressure of 740mmHg and 25 °C. What is the volume of the dry gas at STP? (STP = 1 atm and 0 °C) Vapor Pressure at 25 ° of H₂O equals 24mmHg

20. For a single substance at a specific temperature, which of these characteristics shows the greatest difference when compared among the solid, liquid, and gas phases?

(A) kinetic energy of the molecules in the solid and liquid phases
(B) kinetic energy of the molecules in the liquid and gas phases
(C) distance between the molecules in the solid and liquid phases
(D) distance between the molecules in the liquid and gas phases

21. Which of these substances, when in the solid phase, is expected to have the weakest intermolecular forces?

(A) Ca
(B) C
(C) CaC₂
(D) CO₂

22. Carbon reacts with oxygen according to this equation.

2C(s) + O₂(g) ---> 2CO(g)

DH = -220 kJ

Which statements are true?
1. The reaction is exothermic.
2. The combustion of 0.50 mol of carbon produces 55 kJ of heat energy

(A) 1 only
(B) 2 only
(C) both 1 and 2
(D) neither 1 nor 2

23. Which has the greatest absolute entropy?

(A) one mol of C(s) at 25 °C
(B) one mol of CH₃Cl(l) at 25 °C
(C) one mol of C₂H₆(g) at 25 °C
(D) one mol of C₆H₆(l) at 25 °C

24.

Use these data to calculate DH° for this reaction.

NO(g) + (1/2) O₂(g) ---> NO₂(g)

(A) -57.0
(B) -28.5
(C) +28.5
(D) +57.0

25. A 1.0 g sample of substance A at 100 °C is added to 100 ml of H₂O at 25 °C. Using separate 100 mL portions of H₂O, the procedure is repeated with substance B and then with substance C. How will the final temperatures of the water compare?

(A) T_c > T_b > T_a
(B) T_b > T_a > T_c
(C) T_a > T_b > T_c
(D) T_a = T_b = T_c

26. How many grams of benzene, C₆H₆(l), must be burned in a bomb calorimeter to raise its temperature by 1.5 °C? Given: The calorimeter constant is 12.59 kJ C¯¹ and the DH°:_combustion for C₆H₆ = -491 kJ g¯¹

(A) 0.45 g
(B) 2.8 g
(C) 3.3 g
(D) 8.4 g

27. 2N₂O₅ (g) ---> 4NO₂(g) + O₂(g)

What is the ratio of the rate of decomposition of N₂O₅ to the rate of the formation of NO₂?

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

28. When reacted with water, the insecticides DDT decomposes with a half-life of 10 years. Approximately how many years will it take for 99% of a given sample to decompose once exposed to water in the environment?

(A) 50 yr
(B) 70 yr
(C) 500 yr
(D) 700 yr

29. Which property, if decreased, will cause an increase in the rate of a reaction involving a solid?

(A) temperature
(B) pressure
(C) concentration
(D) particle size

30. Which graph corresponds to the change in concentration of a reacant that is a first order reaction?

31.Which reaction characteristics are changing by the addition of a catalyst to a reaction to a reaction at constant temperature?

1. activation energy
2. equilibrium concentrations
3. reaction enthalpy

(A) 1 only
(B) 3 only
(C) 1 and 2 only
(D) 1, 2, and 3

32. Which reation characteristics will be affected by a change in temperature?

1. value of equilibrium constant
2. equilibrium concentrations

(A) 1 only
(B) 2 only
(C) 1 and 2 only
(D) neither 1 nor 2

33. A water solution of sodium carbonate, Na₂CO₃, has a pH greater than 7 because

(A) it contains more carbonate ions than water molecules.
(B) it contains more sodium ions than carbonate ions.
(C) sodium ions react with water.
(D) carbonate ions react with water.

34. Which species dissociates most completely in water solution?

(A) NH₄⁺
(B) H₂CO₃
(C) HNO₃
(D) HSO₄¯

35. When one mole of (NH₄)₂HPO₄(s) dissolves in water, the number of moles of ions present is closest to which value?

(A) 16
(B) 8
(C) 4
(D) 3

36. The dissociation constant for a certian weak monoprotic acid is 9.0 x 10¯⁵. What is the [H⁺] of a 0.10 M solution of this weak acid that is 0.010 M in the sodium salt of the acid?

(A) 9.0 x 10¯⁶
(B) 9.0 x 10¯⁴
(C) 3.0 x 10¯³
(D) 3.0 x 10¯²

37. According to Bronsted-Lowry Theory, which of these species cannot be amphoteric?

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

38. Which of these solutions, appropriately combined, could be used to produce a buffer?

(A) HCI and NaOH
(B) HNO₂ and NaNO₃
(C) KI and KOH
(D) HF and NaOH

39. The solubility of PbI₂ is 0.0013 mol L¯¹. Use this information to find the K_sp for PbI₂.

(A) 1.7 x 10¯⁶
(B) 6.8 x 10¯⁶
(C) 2,2 x 10¯⁹
(D) 8.8 x 10¯⁹

40. For this reaction, E°_cell = 0.79 V.

6 I¯(aq) + Cr₂O₇²¯(aq) + 14 H⁺ ---> 3 I₂ (aq) + 2 Cr³⁺(aq) + 7 H₂O(aq)

Given that the standard reduction potential for
Cr₂O₇²¯(aq) ---> 2Cr³⁺ (aq) is 1.33 V, what is E°_red for I₂(aq)?

(A) +0.54 V
(B) -0.54 V
(C) +0.18 V
(D) -0.18 V

41. What is the product formed at the anode in the electrolysis of 1.0 M NaNO₃(aq)?

(A) H₂(g)
(B) NO₂(g)
(C) O₂(g)
(D) Na(s)

42. Which of these ions is the best reducing agent?

(A) Fe³⁺
(B) Fe²⁺
(C) Cu²⁺
(D) Cu⁺

43. Zn(s) + Cl₂(g, 1 atm) <===> Zn²⁺(aq, 1 M) + 2Cl¯(aq, 1 M) An electrochemical cell based on this reaction has a cell voltage, E°, of 2.12 V. Which change could make the cell voltage greater than 2.12 V?

(A) add more Zn(s)
(B) add more Cl¯(aq) ions
(C) decrease the concentration of Zn²⁺(aq) ions
(D) decrease the partial pressure of Cl₂

44. What is the total number of p orbitals completely or partially filled in a gaseous silicon atom in its ground state?

(A) 1
(B) 2
(C) 4
(D) 5

45. What is the electron configuration of the Co³⁺ ion?

(A) 1s² 2s²2p⁶ 3s²3p⁶3d⁶
(B) 1s² 2s²2p⁶ 3s²3p⁶3d⁴ 4s²
(C) 1s² 2s²2p⁶ 3s²3p⁶3d⁵ 4s¹
(D) 1s² 2s²2p⁶ 3s²3p⁶3d⁷ 4s²

46. For which element is the "last electron" added to a d orbital?

(A) Ba
(B) Nd
(C) Hf
(D) Pb

47. When the species F¯, Na⁺, and Ne are arranged in order of increasing energy for the removal of an electron, what is the correct order?

(A) F¯ < Na⁺ < Ne
(B) F¯ < Ne < Na⁺
(C) Na⁺ < Ne < F¯
(D) Ne < F¯ < Na⁺

48. Which electronic transition in a hydrogen atom occurs with an energy that corresponds to visible light?

(A) n = 2 ---> n = 1
(B) n = 5 ---> n = 1
(C) n = 4 ---> n = 2
(D) n = 6 ---> n = 3

49. Which species has a Lewis electron structure with one, and only one, unshared pair of valence electrons?

(A) NH₂¯
(B) H₃O⁺
(C) H₂S
(D) CH₄

50. Which compound is expected to have the lowest melting point?

(A) CsF
(B) RbF
(C) KF
(D) NaF

51. Which of these molecules does not contain two pi bonds?

(A) CO
(B) CS₂
(C) H₂CCO
(D) H₂CCH₂

52. Which arrangement shows the bonds H-H, C-C, and Si-Si in order of increasing bond energy?

(A) Si-Si < C-C < H-H
(B) C-C < H-H < Si-Si
(C) H-H < Si-Si < C-C
(D) H-H < C-C < Si-Si

53. Which species has the same general shape as SO₃²¯?

(A) SO₃
(B) NO₃¯
(C) NF₃
(D) CO₃²¯

54. Resonance structures describe molecular structure that have

(A) hybrid orbitals.
(B) rapid equilibria.
(C) electrons that are resonating.
(D) no suitable single Lewis-electron-dot formula.

55. What is the molecular formula of a straight-chain hydrocarbon containing six carbon atoms and one triple bond?

(A) C₆H₈
(B) C₆H₁₀
(C) C₆H₁₂
(D) C₆H₁₄

56. What type of reaction is represented by this equation? C₂H₅OH + HCO₂H ---> HCO₂C₂H₅ + H₂O

(A) addition
(B) esterification
(C) isomerization
(D) saponification

57. Each of these compounds contains only carbon, hydrogen, and oxygen. Which compound has the highest mass percent carbon?

(A) diethyl ether
(B) ethanal
(C) ethanoic acid
(D) propanone

58. How many isomers exist for pentane C₅H₁₂?

(A) two
(B) three
(C) four
(D) five

59. Which pair gives two names for the same compound?

(A) fomaldehyde and methanol
(B) formic acid and ethanoic acid
(C) ethane and ethene
(D) t-butyl alcohol and 2-hydroxy-2-methylpropane

60. Which compound is most soluble in water?

(A) ethylamine
(B) chlorobenzene
(C) methyl acetate
(D) pentane