U.S. National Chemistry Olympiad

1994 Local Test

Notes


1. Which metal reacts most vigorously with water?

(A) Al
(B) Cs
(C) Sr
(D) Ba

2. Which gas dissolves in water to produce a solution that turns phenolphthalein pink?

(A) CH4
(B) H2S
(C) NO2
(D) NH3

3. Which lead salt is most soluble in water?

(A) Pb(C2H3O2)2
(B) PbO2
(C) PbCO3
(D) Pb3(PO4)2

4. Which metal reacts with concentrated NaOH to produce hydrogen gas?

(A) Al
(B) Cu
(C) Fe
(D) Mg

5. Which laboratory measurement is expressed to the appropriate number of significant figures?

(A) 7.92 °C on a thermometer graduated in degrees
(B) 15 seconds on a timer graduated in tenths of seconds
(C) 0.326 cm on a ruler graduated in millimeters
(D) 27.46 mL in a buret graduated in tenths of milliliters

6. Which of the following substances would NOT be expected to react with 1 M HCl?

(A) CaO
(B) SO2
(C) MnO2
(D) K2CO3

7. The percentage of water in an unknown hydrated salt is to be determined by weighing a sample of the salt, heating it to drive off the water, cooling to room temperature and re-weighing. Which procedural mistake would result in determining a percentage of water that is too low?

Procedural Mistakes
I. Heating the sample in a closed, rather than an open, container
II. Reweighing the sample before it has cooled to room temperature

(A) I only
(B) II only
(C) both I and II
(D) neither I nor II

8. When 1.187 g of a metallic oxide is reduced with excess hydrogen, 1.054 g of the metal is produced. What is the metallic oxide?

(A) AgO2
(B) K2O
(C) Cu2O
(D) Tl2O

9. Which equation best represents the ionic reaction that occurs when a copper wire is dipped into a silver nitrate solution?

(A) Cu + AgNO3 ---> Ag + CuNO3
(B) Cu + Ag+ ---> Ag + Cu+
(C) Cu + 2 AgNO3 ---> 2 Ag + Cu(NO3)2
(D) Cu + 2 Ag+ ---> 2 Ag + Cu2+

10. An oxide of nitrogen is found to contain 63.2% oxygen by mass. What is the empirical formula for the oxide?

(A) NO
(B) NO2
(C) N3O3
(D) N2O2

11. When 13.0 g of a hydrocarbon are burned in excess O2, 9.0 g of H2O are formed. What is the formula of the hydrocarbon?

(A) CH4
(B) C2H2
(C) C2H4
(D) C3H8

12. Phosphorus trichloride reacts with water to form phosphorous acid according to this equation.

PCl3 + 3H2O ---> H3PO3 + 3HCl

What is the maximum number of moles of H3PO3 that could be formed when 13.5 g of H2O are reacted with excess PCl3 ?
(A) 0.250
(B) 0.500
(C) 0.750
(D) 4.59

13. How many moles of Na+ ions are present in 75.0 mL of O.123 M Na2CrO4?

(A) 9.22 x 10¯3
(B) 1.38 x 10¯2
(C) 1.84 x 10¯2
(D) 2.77 x 10¯2

14. 60. g of NaOH is dissolved in enough distilled water to make 300 mL of a stock solution. What volumes of this solution and distilled water, when mixed, will result in a solution that is approximately 1 M NaOH?

The Molar Mass of NaOH is 40. g mol¯1

  mL
stock solution
mL
distilled water
(A) 20 80
(B) 20 100
(C) 60 30
(D) 60 90

15. The titration of a 25.00 mL sample of a NaOH solution of unknown concentration required 27.88 mL of 0.159 M H2SO4. What is the molarity of the NaOH?

(A) 0.143
(B) 0.177
(C) 0.285
(D) 0.355

16. Which is predicted to be the most soluble in water?

(A) C2H6
(B) C2H5OH
(C) C2H4Cl2
(D) (C2H5)2O

17. At the same temperature and pressure, samples of oxygen and carbon dioxide gas with equal masses

(A) contain the same number of molecules
(B) occupy equal volumes
(C) possess molecules with the same average velocity
(D) have molecules with the same average kinetic energy

18. The number of moles in 2.50 L (dm3) of nitrogen gas at 100 °C and 700 mm Hg is

(A) 57.1
(B) 2.11
(C) 0.280
(D) 0.0752

19. What is the final pressure (in atm) in this apparatus when equilibrium is reached after the stopcock has been opened? (Assume the volume of the connecting tube to be negligible.)

Ne Ar
0.50 L (dm3) 0.20 L (dm3)
1.25 atm 1.75 atm
(A) 0.5
(B) 1.4
(C) 1.5
(D) 3.0

20. Real gases are most likely to deviate from ideal behavior at conditions of

(A) low T and low P
(B) low T and high P
(C) high T and high P
(D) high T and low P

21) According to this diagram, what phase or phases can be present at point X?

(A) liquid only
(B) liquid and gas only
(C) solid and gas only
(D) liquid and solid only

22) Which changes will increase the vapor pressure of a liquid?

Possible Changes
I. Increasing the temperature
II. Decreasing the atmospheric pressure
III. Increasing the surface area

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

23) When ammonium nitrate, NH4NO3(s) is added to water at 25 °C, it dissolves spontaneously and the temperature of the solution decreases. This indicates that the factor causing the substance to dissolve is a change in

(A) energy
(B) enthalpy
(C) entropy
(D) temperature

24) A student mixes 100 mL of 0.50 M NaOH with 100 mL of 0.50 M HCl in a styrofoam cup and observes a temperature increase of ΔT1. When she repeats this experiment using 200mL of each solution, she observes a temperature change of ΔT2. If no heat is lost to the surroundings or absorbed by the styrofoam cup, what is true about ΔT1 and Δ T2?

(A) ΔT2 = ΔT1
(B) ΔT2 = 0.5 ΔT1
(C) ΔT2 = 2 ΔT1
(D) ΔT2 = 4 ΔT1

25) Which of the relationships is(are) true about water boiling in a container that is open to the atmosphere?

Relationships
I. ΔH = 0
II. ΔS = 0
III. ΔG = 0

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

26) For this reaction at 25 °C, ΔH° = - 1854 kJ and ΔS° = - 236 J K¯1

CH3COCH3(g) + 4 O2(g) ---> 3 CO2(g) + 3 H2O(l)

What is the value of ΔG° for this reaction?

(A) -1784 kJ
(B) -1848 kJ
(C) -1924 kJ
(D) 68500 kJ

27) Given these values of ΔH°:

CS2(l) + 3 O2(g) ---> CO2(g) + 2 SO2(g) ΔH° = - 1077 kJ
H2(g) + O2(g) ---> H2O2(l) ΔH° = - 188 kJ
H2(g) + (1/2) O2(g) ---> H2O(l) ΔH° = - 286 kJ

What is the value of ΔH° for this reaction?

CS2(l) + 6 H2O2(l) ---> CO2(g) + 6 H2O(l) + 2 SO2(g)

(A) -1175 kJ
(B) -1551 kJ
(C) -1665 kJ
(D) -3921 kJ

28) The reaction represented by the equation: xA + yB ---> products
is started by mixing 1.00 mol of A with 2.00 mol of B in a 1.00 L container at a certain temperature. These concentrations are measured after a certain time.

Substance Concentration, M
[A] 0.875
[B] 1.81

Which is the x/y ratio in this reaction?

(A) 1/2
(B) 2/1
(C) 0.875/1.81
(D) 0.125/0.19

29) If the half-life of a reaction is independent of concentration, what is the order of the reaction?

(A) zero
(B) first
(C) second
(D) zero, first, or second

30) A catalyst increases the rate of a reaction by

(A) changing the mechanism of the reaction
(B) increasing the activation energy of the reaction
(C) increasing the concentration of one or more of the products
(D) decreasing the difference in relative energy of the reactants and products

31) The reaction between acetone and bromine in acid solution is represented by the equation:

CH3COCH3(aq) + Br2(aq) + H+(aq) ---> products

These kinetic data are gathered

Initial Concentrations, M  
  CH3COCH3 Br2 H+ Initial Rate, M s¯1
Exp 1 0.30 0.050 0.050 5.8 x 10¯5
Exp 2 0.30 0.100 0.050 5.8 x 10¯5
Exp 3 0.30 0.050 0.100 1.2 x 10¯4
Exp 4 0.40 0.050 0.200 3.2 x 10¯4
Based on these data, the experimental rate law is
(A) Rate = k[CH3COCH3]1[Br2]1[H+]1
(B) Rate = k[CH3COCH3]1[Br2]0[H+]1
(C) Rate = k[CH3COCH3]0[Br2]0[H+]2
(D) Rate = k[CH3COCH3]1[Br2]1[H+]0

32) Which of the following statements about activation energies is true? The activation energy

(A) is the minimum energy needed for a reaction to occur
(B) can be determined from the difference between the energy of reactants and products
(C) is generally smaller for exothermic reactions than for endothermic reactions
(D) is directly related to the rate of molecular collisions

33) The value of an equilibrium constant can be used to predict all of the following except the

(A) direction of a reaction
(B) extent of a reaction
(C) quantity of reactant(s) remaining at equilibrium
(D) time required to reach equilibrium

34) What is the equilibrium expression for this reaction?

2 C(s) + O2(g) <===> 2 CO(g)

(A) K = [CO]/[C][O2]
(B) K = [CO]2/[C]2[O2]
(C) K = [2CO]/[2C][O2]
(D) K = [CO]2/[O2]

35) Consider this reaction at equilibrium, for which the ΔH° = -198 kJ

2 SO2(g) + O2(g) <===> 2 SO3(g)

Which of these changes would cause an increase in the SO3 / SO2 mole ratio?

(A) adding a catalyst
(B) removing O2(g)
(C) decreasing the temperature
(D) decreasing the pressure

36) The Ksp of PbI2(s) is 1.4 x 10¯8 at 25 °C. What is the solubility of PbI2 in moles per liter?

(A) 1.2 x 10¯4
(B) 1.5 x 10¯3
(C) 1.9 x 10¯3
(D) 2.4 x 10¯3

37) Which are strong acids?

Acids
I. HBr
II. HOCl
III. HNO2

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

38) Which represents the most acidic solution?

(A) [H+] = 1 x 10¯4 M
(B) [H+] = 0.3 M
(C) pH = 1.2
(D) pOH = 5.9

39) If 1.12 g of KOH are dissolved in 250 mL of H2O, what is the pH?

The Molar Mass of KOH is 56 g mol¯1

(A) 1.10
(B) 1.70
(C) 12.30
(D) 12.90

40) Which couple is not a conjugate acid-base pair?

(A) HCO3¯ / CO32¯
(B) NH4+ / NH3
(C) H3PO4 / HPO42¯
(D) H3O+ / H2O

41. If 25 mL of 0.055 M HCl are added to 35 mL of distilled H2O, what is the final pH?

(A) 0.20
(B) 1.26
(C) 1.41
(D) 1.64

42. A solution prepared by dissolving 0.100 mole of propionic acid in enough water to make 1.00 L of solution is observed to have a pH = 2.94. What is the Ka for propionic acid?

(A) 1.3 x 10¯6
(B) 1.1 x 10¯3
(C) 1.3 x 10¯5
(D) 1.1 x 10¯2

43. When 0.1M aqueous solutions of the following salts are arranged in order of increasing basicity, what is the correct order?

SALTS
I. NaCl
II. NH4Cl
III. NaHCO3

(A) I < II < III
(B) I < III < II
(C) II < I < III
(D) III < I < II

44. Which is an acid anhydride?

(A) HCl(g)
(B) NH3(g)
(C) CaO(s)
(D) P4O10(s)

45. What species is the ozidizing agent in this equation?

HOCl + H+ + Cl¯ ----> Cl2 + H2O

(A) HOCl
(B) H+
(C) Cl¯
(D) Cl2

46. If solid nickel metal were added to separate aqueous solutions each containing 1M concentrations of Ag+, Cd2+, and Sn2+ ions, how many metals would plate out, based on the given standard reaction potentials?

Standard Reduction Potentials
Ag+/Ag 0.799 V
Sn2+/Sn -0.141 V
Ni2+/Ni -0.236 V
Cd2+/Cd -0.400 V
(A) zero
(B) one
(C) two
(D) three

47. How many electrons are required to balance the half reaction in which dichromate ion, Cr2O72¯ is converted to chromium(III) ions in acid solution?

(A) one
(B) five
(C) six
(D) eight

48. Solutions of Ag+, Cu2+, Fe3+ and Ti4+ are electrolyzed with a constant current until 0.10 mol of metal is deposited. Which will require the greatest length of time?

(A) Ag+
(B) Cu2+
(C) Fe3+
(D) Ti4+

49. What type of radiation is emitted during a nuclear process in which a nucleas with a greater atomic number is formed?

(A) alpha particles
(B) beta particles
(C) positrons
(D) gamma rays

50. Which pair of elements is listed in order of decreasing first ionization energy?

(A) Na, Mg
(B) Mg, Al
(C) Al, Si
(D) Si, P

51. Which is the best electrical conducter?

(A) C
(B) Si
(C) Ge
(D) Sn

52. Which atom will be the smallest?

(A) Si (Z = 14)
(B) P (Z = 15)
(C) Ge (Z = 32)
(D) As (Z = 33)

53. An element with a low melting point that does not conduct electricity would most likely be found on the periodic table

(A) in the upper right portion
(B) in the upper left portion
(C) in the lower left portion
(D) in the middle

54. The first three ionization energies of an element X are 590, 1145, and 4912 kJ/mol. The most likely formula for a stable ion of X is

(A) X+
(B) X2+
(C) X3+
(D) X¯

55. The highest oxidation state known for vanadium (Z = 23) is

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

56. Which have both ionic and covalent bonds?

SALTS
-------------
I. NH4Br
II. NaNO2

(A) I only
(B) II only
(C) both I and II
(D) neither I or II

57. How many valence electrons are present in the tetraborate ion (B4O72¯)?

(A) 42
(B) 54
(C) 56
(D) 62

58. Which substance has the highest melting point?

(A) silicon carbide, SiC
(B) phosphorus pentachloride, PCl5
(C) sulfer, S8
(D) phosgene, COCl2

59. All of the following species are pyramidal in shape except

(A) SO32¯
(B) NH3
(C) BF3
(D) H3O+

60. In which compounds in the liquid state does hydrogen bonding occur?

Compounds
-----------------
I. ammonia
II. hydrogen peroxide
III. methane

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