U.S. National Chemistry Olympiad: 1999 Local Section Test

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1. Which oxide forms a basic solution when mixed with water?

(A) K₂O
(B) Al₂O₃
(C) CO₂
(D) SO₃

2. Which of these compounds is not white?

1. KMnO₄
2. ZnSO₄
3. FeCl₃

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

3. Which gas will cause a solution containing potassium iodide and starch to turn a blue-black color?

(A) H₂
(B) CO₂
(C) Cl₂
(D) NH₃

4. A colorless aqueous solution contains a single ionic compound. Use this experimental information to deduce the identity of the compound.

* When a small amount of dilute NaOH solution is added to the solution, a precipitate forms. This precipitate dissolves when excess NaOH is added.
* Addition of AgC₂H₃O₂ to the solution gives a white precipitate.

(A) AlCl₃
(B) Ba(NO₃)₂
(C) CuSO₄
(D) FeI₂

5. The most active metals on the periodic table have

(A) large radii and high electronegativities.
(B) small radii and low electronegativities.
(C) small radii and low ionization energies.
(D) large radii and low ionization energies.

6. The aqueous solubilities of several compounds between temperatures of 0 °C and 80 °C are shown in this diagram. Which compound can be recovered with the highest percent yield by dissolving a sample in water at 80 °C and cooling to 0 °C?

(A) A
(B) B
(C) C
(D) D

7. A student determines the concentration of a solution of NaOH. She pipets a sample of the NaOH solution into a flask and adds two drops of an indicator. Standardized acid is added from a buret until the indicator changes color. Which device may contain residual water without affecting the results of the titration?

1. buret
2. flask
3. pipet

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

8. The density of a block of metal is determined by weighing it, then submerging it in water. Based on these data, to how many significant figures should the density be reported?

Data
mass of block	25.472 g
volume of H2O	10.5 mL
volume of H2O with block	20.0 mL

(A) 2
(B) 3
(C) 4
(D) 5

9. Arsenic(III) sulfide reacts with oxygen to form arsenic(III) oxide and sulfur(IV) oxide as represented by this equation.

__As₂S₃ + __O₂ ---> __As₂O₃ + __SO₂

What is the coefficient for O₂ when this equation is balanced using whole number coefficients?

(A) 5
(B) 7
(C) 9
(D) 11

10. How many grams of MgCO₃ contain 24.0 g of oxygen? (The molar mass of MgCO₃ is 84.3 g mol¯¹)

(A) 42.2 g
(B) 84.3 g
(C) 126 g
(D) 154 g

11. How many hydrogen atoms are present in one mole of ammonium benzoate, NH₄C₇H₅O₂?

(A) 6.0 x 10²³
(B) 2.4 x 10²⁴
(C) 3.0 x 10²⁴
(D) 5.4 x 10²⁴

12. Consider this balanced equation:

3 H₂(g) + CO(g) ---> CH₄(g) + H₂O(g)

How many moles of CH₄ can be obtained by reacting 2.0 mol of H₂ with 2.0 mol CO according to this equation?

(A) 0.33 mol
(B) 0.67 mol
(C) 2.0 mol
(D) 3.0 mol

13. What is the molarity of the chloride ion in 250 mL of a solution containing 1.90 g of MgCl₂? (The molar mass of MgCl₂ is 95.2 g mol¯¹

(A) 0.020 M
(B) 0.040 M
(C) 0.080 M
(D) 0.16 M

14. Consider this equation.

2 SO₂(g) + O₂(g) --> 2 SO₃(g)

What happens to the total volume when 3.0 L of SO₂ and 2.0 L of O₂ react to form the maximum amount of SO₃ possible from these volumes of reactants. Assume all gases are at the same constant temperature and pressure.

(A) It decreases by 1.5 L.
(B) It decreases by 1.0 L.
(C) It increases by 0.50 L.
(D) It remains constant.

15. What is the molarity of an H₂SO₄ solution if 25.00 mL is exactly neutralized by 32.63 mL of 0.164 M NaOH?

(A) 0.107 M
(B) 0.126 M
(C) 0.214 M
(D) 0.428 M

16. Which element exists as a solid at 25 °C and one atmosphere of pressure?

(A) bromine
(B) chlorine
(C) mercury
(D) phosphorus

17. "Dry ice" is solid carbon dioxide. To which class of solids does it belong?

(A) amorphous solid
(B) molecular solid
(C) network solid
(D) polymeric solid

18. Which of these factors affect the average kinetic energy of the molecules in a gas?

1. pressure
2. temperature

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

19. How does the vapor pressure of a liquid in a stoppered flask change if the quantity of liquid is doubled?

(A) It doubles
(B) It increases slightly
(C) It decreases.
(D) It does not change.

20. What type of forces must be overcome when liquid ammonia vaporizes?

1. covalent bonds
2. dispersion forces
3. hydrogen bonds

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

21. The temperature of a gas sample is increased from 50 °C to 100 °C. By what factor must the pressure be changed if the volume is to be kept constant?

(A) 0.5
(B) 0.87
(C) 1.15
(D) 2.0

22. What is the molar mass of a gas that diffuses twice as fast as SO₂? (The molar mass of SO₂ is 64 g mol¯¹)

(A) 16 g mol¯¹
(B) 32 g mol¯¹
(C) 128 g mol¯¹
(D) 256 g mol¯¹

23. How many grams of ice at 0 °C can be melted by the addition of 500 J of heat? (The molar heat of fusion for ice is 6.02 kJ mol¯¹)

(A) 0.0831 g
(B) 1.50 g
(C) 3.01 g
(D) 12.0 g

3 O₂(g) --> 2 O₃(g)

24. This reaction is endothermic. What can be concluded about the average energy per bond in O₂ and O₃?

(A) The average energy per bond in O₂ is greater than the average energy per bond in O₃.
(B) The average energy per bond in O₂ is less than the average energy per bond in O₃.
(C) The average energy per bond in O₂ is the same as the average energy per bond in O₃.
(D) No conclusion can be drawn about the average bond energies from this information alone.

25. Under which set of conditions is a chemical reaction most likely to be spontaneous?

	DH	DS	T (temperature)
(A)	-	-	low
(B)	-	-	high
(C)	+	+	low
(D)	+	-	high

26. For which reaction do you expect DS to be negative?

(A) 2C(s) + O₂(g) --> 2CO(g)
(B) Br₂(s) --> Br₂(l)
(C) H₂O(l, 25 °C) --> H₂O(l, 50 °C)
(D) Cl₂(g) + 2HI(g) --> I₂(s) + HCl(g)

27. According to this information, and given the fact that for water, DH = -286 kJ mol¯¹, what is DH for MgO(s)?

(A) -904 kJ mol¯¹
(B) -602 kJ mol¯¹
(C) -334 k J mol¯¹
(D) -30 kJ mol¯¹

28. The rate of a reaction with just two reactants is observed to double when the concentration of one reactant is doubled and the second reactant is held constant. The rate is also observed to increase by a factor of nine when the concentration of the second reactant is tripled, holding the concentration of the first reactant constant. What is the overall order for this reaction?

(A) 2
(B) 3
(C) 5
(D) 6

29. Which energy diagram represents a highly exothermic reaction that has a small activation energy? (Assume that all curves are plotted on the same scale.)

30. Tritium decays by a first-order process that has half-life of 12.5 years. How many years will it take to reduce the radioactivity of a tritium sample to 15% of it original value?

(A) 64 y
(B) 54 y
(C) 34 y
(D) 24 y

31. What is the overall order of a reaction with a rate constant having the units L mol¯¹ s¯¹?

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

32. In a reaction with several steps, which step limits the rate of the reaction?

(A) first
(B) last
(C) fastest
(D) slowest

P₄(s) + 5 O₂(g) <===> P₄O₁₀(s)

33. What is the equilibrium expression for this reaction?

(A) K_c = [P₄O₁₀] / [P₄] [O₂]⁵
(B) K_c = [P₄O₁₀] / 5 [P₄] [O₂]
(C) K_c = [O₂]⁵
(D) K_c = 1 / [O₂}⁵

Fe₃O₄(s) + 4 H₂(g) <===> 3 Fe(s) + 4 H₂O(g)
DH > 0

34. For this reaction at equilibrium, which changes will increase the quantity of Fe(s)?

1. increasing temperature
2. decreasing temperature
3. adding Fe₃O₄(s)

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

35. Which 0.1 M solution has the highest pH?

(A) sodium carbonate
(B) sodium chloride
(C) ammonium carbonate
(D) ammonium chloride

36. Which is the strongest acid?

(A) acetic acid - (K_a = 1.8 x 10¯⁵)
(B) benzoic acid - (K_a = 6.3 x 10¯⁵)
(C) formic acid - (K_a = 1.8 x 10¯⁴)
(D) nitrous acid - (K_a = 6.0 x 10¯⁴)

37. What is the order of concentration of the ions and molecules in a nitrous acid solution? Nitrous acid, HNO₂, is a weak acid.

(A) H₃O⁺ = NO₂¯ > HNO₂ > OH¯
(B) H₃O⁺ = NO₂¯ = HNO₂ = OH¯
(C) HNO₂ > H₃O⁺ = NO₂¯ > OH¯
(D) HNO₂ > NO₂¯ > H₃O⁺ > OH¯

38. Which acid, together with its sodium salt, would be best for preparing a buffer with a pH = 4.5?

(A) HCN - (K_a = 4.9 x 10¯¹⁰)
(B) C₃H₅O₂H - (K_a = 1.3 x 10¯⁵)
(C) HF - (K_a = 6.8 x 10¯⁴)
(D) ClC₂H₂O₂H - (K_a = 1.4 x 10¯³)

39. What is the pH of a solution that contains 0.50 M sodium benzoate and 0.75 M benzoic acid? (K_a= 6.8 x 10¯⁵)

(A) 3.99
(B) 4.34
(C) 4.57
(D) 5.22

40. The solubility of lead(II) carbonate is 2.7 x 10¯⁷ mol L¯¹. What is its K_sp?

(A) 5.2 x 10¯⁴
(B) 2.7 x 10¯⁷
(C) 7.3 x 10¯¹⁴
(D) 3.9 x 10¯²⁰

S₄O₆²¯ + 10 H₂O --> 4 SO₄²¯ + 20 H⁺ + 14 e¯

41. What is the change in oxidation number of sulfur in the half-reaction?

(A) -2 to -8
(B) +4 to +1
(C) +4 to +6
(D) +2 1/2 to +6

HAsO₂(aq) + Sn²⁺(aq) + H⁺(aq) --> As(s) + An⁴⁺(aq) + H₂O(l)

42. What is the oxidizing agent in the unbalanced equation?

(A) HAsO₂(aq)
(B) Sn²⁺(aq)
(C) H⁺(aq)
(D) Sn⁴⁺(aq)

43. According to the E values, what is the potential for this reaction under standard conditions?

Sn(s) + 2 Fe³⁺(aq) ---> 2 Fe²⁺(aq) + Sn²⁺(aq)

(A) 1.68 V
(B) 1.40 V
(C) 0.91 V
(D) 0.63 V

44. When a sample of molten sodium chloride is electrolyzed for a given length of time, how do the number of moles of sodium metal and chlorine gas produced compare?

(A) The moles of sodium metal are equal to the moles of chlorine gas.
(B) There are twice as many moles of sodium metal as as moles of chlorine gas
(C) There are three times as many moles of sodium metal as moles of chlorine gas.
(D) There are four times as many moles of sodium metal as moles of chlorine gas.

45. Which element has a partially-filled f subshell?

(A) Ba
(B) Eu
(C) Re
(D) Bi

46. How many orbitals have the quantum numbers n = 4 and l = 2?

(A) 1
(B) 3
(C) 5
(D) 7

47. Which element has the highest second ionization energy?

(A) Be
(B) Li
(C) B
(D) C

48. Which ion in the gaseous state has the greatest number of unpaired electrons?

(A) Ni²⁺
(B) Cu²⁺
(C) Zn²⁺
(D) Ge²⁺

49. Which property decreases crossing the periodic table from left to right and increases from top to bottom?

(A) ionization energy
(B) electron affinity
(C) electronegativity
(D) atomic radius

50. Which compound contains both covalent and ionic bonds?

(A) calcium oxide, CaO
(B) methyl fluoride, CH₃F
(C) sodium peroxide, Na₂O₂
(D) hypochlorous acid, HOCl

51. Which species has a Lewis structure most like that of CO₃²¯?

(A) NO₃¯
(B) BCl₃
(C) NCl₃
(D) SO₃²¯

52. Which element has the greatest electronegativity?

(A) As
(B) Ge
(C) P
(D) Sb

53. Which element has the highest melting point?

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

54. For which pair of species is the hybridization of the central atom the same?

(A) NH₃, NH₄⁺
(B) NO₂⁺ , NO₂¯
(C) PF₃, PF₅
(D) BF₃, BF₄¯

55. Arrange the species in order of decreasing H-N-H bond angle.

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

56. How many moles of water would be produced by the complete combustion of one mole of benzene, C₆H₆, in excess oxygen?

(A) 2
(B) 3
(C) 4
(D) 6

57. Ketene has the formula H₂C=C=O. How many sigma and pi bonds does it have?

	sigma bonds	pi bonds
(A)	6	2
(B)	6	0
(C)	4	2
(D)	2	2

58. The prefixes used to designate organic compounds with 3 and 4 carbon atoms are, respectively,

(A) tri- and tetra-
(B) tri- and quatr-
(C) ter- and prop-
(D) prop- and but-

59. Which functional group is characteristic of proteins?

60. Which substance is most likely to be used as a soap?

(A) CH₃(CH₂)₁₂CO₂CH₃
(B) CH₃(CH₂)₅O(CH₂)₅CH₃
(C) CH₃(CH₂)₁₂CO₂Na
(D) CH₃(CH₂)₁₂CHCl₂