Make your own free website on Tripod.com

U.S. National Chemistry Olympiad

1997 Local Section Test

Notes


1. Which gas is least soluble in water?

(A) H2
(B) CO2
(C) NH3
(D) SO2

2. Identify every process that is a chemical change.

1. cooling
2. evaporating
3. rusting

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

3. Which element is expected to have the lowest melting point and the lowest density?

(A) Ag
(B) K
(C) Co
(D) Al

4. Which compound is not expected to be colored?

(A) CuCl2
(B) K2Cr2O7
(C) MnO2
(D) TiO2

5. Which pair of substances can dissolve in water to give 0.1 M solutions and will produce a precipitate when they are mixed?

(A) NaOH and BaCl2
(B) Na2CO3 and HClO4
(C) MgSO4 and Pb(NO3)2
(D) CaCl2 and Zn(C2H3O2)2

6. Calculate the density of a gold coin from the given data.
Table of Data
Mass of the gold coin 13.5243 g
Volume of the coin and water 22.9 mL
volume of the water alone 22.2 mL

(A) 19.32 g mL¯1
(B) 19.3 g mL¯1
(C) 19 g mL¯1
(D) 2 x 101g mL¯1

7. A typical silicon chip such as those in electronic calculators weighs 2.3 x 10¯4g. How many silicon atoms are in such a chip?

(A) 4.9 x 1018
(B) 1.4 x 1020
(C) 3.9 x 1021
(D) 2.6 x 1027

8. What is the coefficent for oxygen when this equation is balanced?

___H2S(g) +___O2(g) ---> ___SO3(g) +___H2O(l)

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

9. The first step in the Ostwald process for producing nitric acid, HNO3, from ammonia is represented by this equation.

4NH3(g) + 5O2(g) ---> 4NO(g) + 6H2O(g)

What volume of oxygen is needed to produce each liter of NO?

(A) 0.80 L
(B) 1.20 L
(C) 5.00 L
(D) 22.4 L

10. Antimony reacts with sulfur according to this equation.

2Sb(s) + 3S(s) ---> Sb2S3(s)

The molar mass of Sb2S3 is 339.7 g mol¯1

What is the percentage yield for a reaction in which 1.40 g of Sb2S3 is obtained from 1.73 g of antimony and a slight excess of sulfur?

(A) 80.9%
(B) 58.0%
(C) 40.5%
(D) 29.0%

11. The limiting reagent in a particular reaction can be recognized because it is the reagent.

(A) with the smallest coefficient in the balanced equation.
(B) that has the lowest mass in the reaction mixture.
(C) that is present in the smallest molar quantity.
(D) that would be used up first.

12. What mass of oxygen is present in 50.0 g of copper(II) sulfate pentahydrate, CuSO4 . 5H2O? The molar mass of CuSO4 . 5H2O is 249.68 g mol¯1

(A) 12.8 g
(B) 16.0 g
(C) 20.0 g
(D) 28.8 g

13. What mass of calcium chloride hexahydrate must be disolved in sufficient water to prepare 200 mL of a solution with a chloride ion concentration of 0.50M? The molar mass of CaCl2 . 6H2O is 219 g mol¯1

(A) 5.6 g
(B) 11 g
(C) 22 g
(D) 44 g

14. The major commercial source for bromine is deep brine wells in Arkansas where the concentration of bromide ion can be as high as 5000 parts per million by mass. What is this concentration when expressed as a mass percentage?

(A) 0.005%
(B) 0.05%
(C) 0.5%
(D) 5%

15. A sodium hydroxide solution is to be standardized by pipetting 20.0 mL aliquots of it into conical flasks and titrating with a standard acid solution delivered from a buret. In which pieces of glassware can traces of water remain without affecting the results of the experiment?

1. buret
2. conical flask
3. pipet

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

16. A certain solid is insoluble in water. It does not conduct electricity in the solid state but does conduct electricity when melted. What type of solid is it?

(A) ionic
(B) metallic
(C) molecular
(D) network covalent

17. During the part of the cycle when heat is removed from the food compartment of an electric refrigerator, the refrigerant undergoes a change from a

(A) liquid to a gas.
(B) gas to a liquid.
(C) liquid to a solid.
(D) solid to a liquid.

18. When the substances CCl4, CF4, and CH4 are arranged in order of increasing boiling point (with the lowest boiling substance first), what is the correct order?

(A) CCl4 < CF4 < CH4
(B) CH4 < CF4 < CCl4
(C) CF4 < CCl4 < CH4
(D) CF4 < CH4 < CCl4

19. 30.0 mL of water at 10. °C is mixed with 50.0 mL of water at 60. °C. What is the final temperature of the mixture?

(A) 31 °C
(B) 35 °C
(C) 41 °C
(D) 46 °C

20. A mixture of several gases is prepared for a series of photosynthesis experiments. If the mixture contains 0.060 mol of O2(g), 0.30 mol of N2(g), 0.030 mol of CO2(g), and 0.010 mol of H2O(g) and exerts a total pressure of 1.20 atm, what is the partial pressure of CO2 in this mixture?

(A) 1.2 atm
(B) 0.36 atm
(C) 0.090 atm
(D) 0.075 atm

21. The molar mass of a volatile liquid is to be determined by adding a sample of it to a pre-weighed 125 mL a conical flask covered with a piece of aluminum foil with a pinhole in it. After heating the flask in a boiling water bath to vaporize the liquid, the outside of the flask is dried and the flask is reweighed. What is the molar mass of the volatile liquid?
Table of Data
Mass of empty flask 63.427 g
Mass of flask with vapor 63.768 g
Atmospheric pressure 748 mm Hg

(A) 44.0 g mol¯1
(B) 670 g mol¯1
(C) 84.9 g mol¯1
(D) 166 g mol¯1

22. Consider two 1.0 L flasks at the same temperature. One flask contains ammonia gas and the second contains an equal number of moles of sulfur dioxide gas. Which of these characteristics will be the same for both gases?

1. average molecular velocity
2. density
3. pressure

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

23. The compound C2F4HCl is currently being considered as a replacement for CBrF3 as a fire extinguishing agent because C2F4HCl does not deplete ozone. What are the most probable products if a molecule of C2F4HCI is bombarded with high energy photons?

Bond Bond Energy
kJ mol¯1
C-C 346
C-Cl 327
C-F 485
C-H 411
(A) CF3 + CFHCl
(B) C2F3HCl + F
(C) C2F4H + Cl
(D) C2F4Cl + H

24 What is the value of DH° for this reaction?

Fe2O3(s) + 3H2O(l) ---> 2Fe(OH)3(s)

Substance Df
kJ mol¯1
Fe2O3(s) -824.2
Fe(OH)3(s) -823.0
H2O(l) -285.8
(A) 35.6 kJ
(B) 286 kJ
(C) 858.6kJ
(D) -536 KJ

25. When Na2S2O3 . 3H2O dissolve in water, the solution gets cold. Which energy diagram best represents the behavior of this solution process?

26. For which of these processes would DS° be expected to be the most positive?

(A) O2(g) + 2H2(g) ---> 2H2O(g)
(B) H2O(l) ---> H2O(s)
(C) N2O4(g) ---> 2NO2(g)
(D) NH4NO2(s) ---> N2(g) + 2H2O(g)

27. A plot of reactant concentration versus time gives a straight line. What is the order of the reaction for this reactant?

(A) zero
(B) first
(C) second
(D) some other value

28. Which chage does not increase the value of the rate constant for a reaction?

(A) decreasing the activation energy
(B) raising the temperature
(C) adding a catalyst
(D) increasing the concentration of reactants

29. A certain reaction has a DH = -75 kJ and an activation energy of 40 kJ. A catalyst is found that lowers the activation energy of the forward reaction by 15 kJ. What is the activation energy of the reverse reaction in the presence of this same catalyst?

(A) 25 kJ
(B) 60 kJ
(C) 90 kJ
(D) 100 kJ

30. Nitrogen(II) oxide and hydrogen react to form nitrogen and water according to this equation.

2NO(g) + 2H2 ---> N2(g) + 2H2O(g)

According to these experimental results, what are the orders for NO and H2O?

[NO] [H2] Rate
(M min¯1)
0.015 0.020 0.60
0.015 0.040 1.20
0.030 0.020 2.40
  Order,NO Order,H2
(A) 1 1
(B) 1 2
(C) 2 1
(D) 2 2

31. At a certain temperature the first-order decomposition of hydrogen peroxide exhibits these data.

time (seconds, s) [H2O2]
(mol L¯1)
0 2.0
15 1.0

At what time will the [H2O2] = 0.50 mol L¯1?

(A) 30. s
(B) 25 s
(C) 22 s
(D) 20. s

32. What is the relationship between the equilibrium constant (Kc) of a reaction and the rate constants for the foward (kf) and backward (kb) steps?

(A) Kc = kf kb
(B) Kc = kb / kf
(C) Kc = kf / kb
(D) Kc = 1 / (kfkb)

33. Xenon tetrafluoride, XeF4, can be prepared by heating Xe and F2 together according to this equation.

Xe(g) + 2F2(g) <===> XeF4(g)

What is the equilibrium expression for this reaction?

(A) K = [XeF4] / ( [Xe] [F2] )
(B) K = [XeF4] / ( 2[Xe] [F2] )
(C) K = [XeF4] / ( [Xe] [F2]2 )
(D) K = ( [Xe] [F2] ) / [XeF4]

34. Which acid reacts with NaOH to form sodium hypochlorite (the ingredient in household bleach)?

(A) HOCl
(B) HOClO
(C) HOClO2
(D) HOClO3

35. Which of these acids is the strongest in aqueous solution?

(A) H3PO4
(B) H2SO3
(C) HClO3
(D) HOCl

36. Which pair of chemicals would produce a buffer solution when equal numbers of moles of each are mixed?

(A) HF and NaF
(B) HF and HC2H3O2
(C) HCl and NH3
(D) HNO2 and NaOH

37. Normal rain water has a pH of 5.6. This is best explained by the presence of

(A) nitrogen oxides.
(B) carbon dioxide.
(C) sulfur oxides.
(D) particulates.

38. In a 0.050 M solution of a weak monoprotic acid, [H+]= 1.8 x 10¯3. What is its Ka?

(A) 3.6 x 10¯2
(B) 9.0 x 10¯5
(C) 6.7 x 10¯5
(D) 1.6 x 10¯7

39. Which titration will have an equivalence point at the lowest pH?

(A) HCl and KOH
(B) HF and NaOH
(C) HF and NH3
(D) HCl and NH3

40. Which product(s) would be formed when saturated solutions of calcium hydroxide and ammonium chloride are mixed?

1. ammonia gas
2. calcium chloride precipitate
3. calcium diammine ion

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

41. An aqueous solution containing KF, KBr and KI is treated with chlorine water. Which product(s) would be formed?

(A) fluorine only
(B) bromine only
(C) bromine and iodine
(D) fluorine and iodine

42. Calculate the voltage of a cell using this reaction at standard conditions.

Sn + 2 Ag+ ---> Sn2+ + 2 Ag
Reduction Potentials, E°
Sn2+ + 2e ¯ ---> Sn -0.14 V
Ag+ + e ¯ ---> Ag 0.80 V

(A) 0.66 V
(B) 0.94 V
(C) 1.46 V
(D) 1.74 V

43. What is the function of H2O2 in this reaction?

6 H+ + 2 MnO4¯ + 5 H2O2 ---> 2 Mn2+ + 5 O2 + 8 H2O

(A) catalyst
(B) reducing agent
(C) oxidizing agent
(D) inhibitor

44. How much hydrogen is produced from the electrolysis of water in the same time that 2.2 L of oxygen is formed?

(A) 0.14 L
(B) 1.1 L
(C) 2.2 L
(D) 4.4 L

45. Which of these changes will cause the value of the potential for this half-reaction to be less negative? (E° = -0.28 V for the reaction.)

Co2+(aq) + 2 e¯ ---> Co(s)

(A) increasing the amount of solid Co
(B) decreasing the amount of solid Co
(C) increasing the concentration of Co2+(aq)
(D) decreasing the concentration of Co2+(aq)

46. In which pair are the two species both isoelectronic and isotopic?

[Reader's Note: due to the limitations of HTML, the value superscripted left could not be placed directly over (in its proper position) the value subscripted left.]

(A) 4020Ca2 and 4018Ar
(B) 3919K+ and 4019K+
(C) 2412Mg2+ and 2512Mg
(D) 5626Fe2+ and 5726Fe3+

47. Which emission line in the hydrogen spectrum occurs at the highest frequency?

(A) n = 3 ---> n = 1
(B) n = 5 ---> n = 2
(C) n = 7 ---> n = 5
(D) n = 10 ---> n = 8

48. Which species has this electron arrangement? 1s2 2s22p6 3s23p63d10

(A) Ni
(B) Ni2+
(C) Zn
(D) Zn2+

49. When the species Ar, Cl¯, and K+ are arranged in order of increasing size (with the smallest species first), what is the correct order?

(A) Cl¯ < Ar < K+
(B) K+ < Cl¯ < Ar
(C) K+ < Ar < Cl¯
(D) Ar < K+ < Cl¯

50. Which species contains both covalent and ionic bonds?

(A) NH3BF3
(B) H3O+
(C) NaKS
(D) Mg(CN)2

51. These two electron dot formulas for carbon dioxide both satisfy the octet rule but one is preferred over the other. Which of the statements below identifies the preferred structure and the reason it is preferred?

(A) Structure A is preferred because the triple bond is stronger than a double bond.
(B) Structure A is preferred because there is a greater formal charge on the atoms.
(C) Structure B is preferred because the formal charges on the atoms are zero.
(D) Structure B is preferred because the bonds are equal.

52. Which molecule is polar?

(A) AsCl5
(B) SiCl4
(C) ClF3
(D) SF6

53. How many sigma and pi bonds are present in CH2CHCO2H?

(A) 10 sigma
(B) 8 sigma, 2 pi
(C) 7 sigma, 2 pi
(D) 6 sigma, 2 pi

54. What is the hydridization of nitrogen in dinitrogen tetroxide, N2O4?

(A) sp3
(B) sp2
(C) sp
(D) dsp2

55. When the carbon-carbon bonds in ethane (C2H6), ethene (C2H4), and benzene (C6H 6) are arranged in order of increasing length (shortest bond first), what is the correct order?

(A) C2H6 < C2H4 < C6H6
(B) C2H4 < C2H6 < C6H6
(C) C6H6 < C2H4 < C2H6
(D) C2H4 < C6H6 < C2H6

56. This condensed structural formula represents a

(A) primary alcohol.
(B) secondary alcohol.
(C) tertiary alcohol.
(D) quaternary alcohol.

57. Methanol is oxidized gently. The carbon containing oxidation product is

(A) methanal (formaldehyde).
(B) methanoic (formic) acid.
(C) carbon monoxide.
(D) carbon dioxide.

58. Which is the strongest acid in aqueous solution?

(A) HCOOH
(B) CH3COOH
(C) H2NCH2COOH
(D) ClCH2COOH

59. Which formula represents the greatest number of isomers?

(A) C2H2Cl2
(B) C2HCl3
(C) C2H4Cl2
(D) C2H3Cl3

60. A compound with the formula C3H6O produces hydrogen when reacted with sodium metal. The compound is most likely to be

(A) an alcohol.
(B) an aldehyde.
(C) an ether.
(D) a ketone.