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U.S. National Chemistry Olympiad

1999 National Test

Notes


1. Which substance is most likely to be soluble in a nonpolar solvent?

(A) glucose
(B) graphite
(C) lithium fluoride
(D) sulfur

2. A solution of which substance can best be used as both a titrant and its own indicator in an oxidation-reduction titration?

(A) I2
(B) NaOCl
(C) K2Cr2O7
(D) KMnO4

3. What value of DT should be used for the calorimetry experiment that gives these graphed results?

(A) 10 °C
(B) 12 °C
(C) 15 °C
(D) 19 °C

Fe3+(aq) + SCN¯(aq) <===> FeSCN2+(aq)

4. The equilibrium constant for this reaction can best be determined by means of

(A) chromatography.
(B) conductance.
(C) ion exchange.
(D) spectrophotmetry.

5. Which solid reacts with dilute hydrochloric acid at 25 °C to produce a gas that is more dense than air?

(A) Zn
(B) Pb(NO3)2
(C) NaBr
(D) NaHCO3

6. A 20.00 mL sample of a Ba(OH)2 solution is titrated with 0.245 M HCl. If 27.15 mL of HCl is required, what is the molarity of the Ba(OH)2 solution?

(A) 0.166 M
(B) 0.180 M
(C) 0.333 M
(D) 0.666 M

7. When ionic hydrides react with water, the products are

(A) acidic solutions and hydrogen gas.
(B) acidic solutions and oxygen gas.
(C) basic solutions and hydrogen gas.
(D) basic solutions and oxygen gas.

8. 0.250 g of an element, M, reacts with excess fluorine to produce 0.547 g of the hexafluoride, MF6. What is the element?

(A) Cr
(B) Mo
(C) S
(D) Te

9. How many moles of Na+ ions are in 20 mL of 0.40 M Na3PO4?

(A) 0.0080
(B) 0.024
(C) 0.050
(D) 0.20

10. What is the mass percent of oxygen in Al2(SO4)3 . 18 H2O (The molar mass of this substance is 666.43 g / mol)?

(A) 9.60
(B) 28.8
(C) 43.2
(D) 72.0

_Mn2+(aq) + _BiO3¯(aq) + _H+(aq) <===> _Bi3+(aq) + _MnO4¯(aq) + _H2O (l)

11. What is the coefficient for H+(aq) when the equation is balanced with whole number coefficients?

(A) 3
(B) 4
(C) 7
(D) 14

12. What is the number of O2 molecules in the 2.5 g of O2 inhaled by the average person in one minute?

(A) 1.9 x 1022
(B) 3.8 x 1022
(C) 4.7 x 1022
(D) 9.4 x 1022

13. Which point in the phase diagram best represents supercritical conditions?

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

14. The vapor pressure of a liquid in a closed container depends on

1. temperature of the liquid
2. quantity of liquid
3. surface area of the liquid
(A) 1 only
(B) 2 only
(C) 1 and 3 only
(D) 1,2 and 3

15. What is the maximum number of phases that can be in equilibrium in a one component system?

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

16. The molar mass of a gas with a density of 5.8 g L¯1 at 25 °C and 740 mmHg is closest to

(A) 10 g mol¯1
(B) 20 g mol¯1
(C) 150 g mol¯1
(D) 190 g mol¯1

17. Which substance would be expected to exhibit the greatest surface tension at 25 °C?

(A) CH3OCH3
(B) C2H5OH
(C) CH3CH(OH)CH3
(D) CH2(OH)CH2OH

3 N2O(g) + 2 NH3(g) ---> 4 N2(g) + 3 H2O(g)
DH = -879.6 kJ

18. What is the Df for N2O in kJ mol¯1 (heats of formation: NH3 = -45.9 kJ mol¯1 and H2O = -241.8 kJ mol¯1) ?

(A) +246
(B) +82
(C) -82
(D) -246

19. What is the change in internal energy, DE, for a reaction that gives off 65 joules of heat and does 38 joules of work?

(A) -103 J
(B) -27 J
(C) +27J
(D) +103 J

20. What are the signs of DH and DS for this reaction: 2C(s) + O2(g) ---> 2CO2(g) ?

 DHDS
(A)--
(B)-+
(C)++
(D)+-

21. The rate of formation of O3(g) is 2.0 x 10¯7 mol L¯11 for the reaction: 3 O2(g) ---> 2 O3(g)

What is the rate of disappearence of O2(g) in mol L¯11?

(A) 1.3 x 10¯7
(B) 2.0 x 10¯7
(C) 3.0 x 10¯7
(D) 4.5 x 10¯7

22. Which statements are true?

1. S° values for all elements in their standard states are positive
2. S° values for all aqueous ions are positive.
3. DS° values for all spontaneous reactions are positive.
(A) 1 only
(B) 1 and 2 only
(C) 2 and 3 only
(D) 1,2 and 3

23. For this reaction, k = 1.7 x 107 at 25 °C. What is the value of DG° in kJ?

Ag+(aq) + 2 NH3(aq) <===> Ag(NH3)2+(aq)

(A) -41.2
(B) -17.9
(C) +17.9
(D) +41.2

24. The value of DH for a reaction can be found by appropriate combination of bond enthalpies (the energy required to break a particular bond, represented BE). Which expression will give DH for this reaction?

C2H4(g) + H2(g) ---> C2H6(g)

(A) BEC=C +BEH-H - [BEC-C + 2BEC-H]
(B) BEC-C + 2BEC-H - [BEC=C + BEH-H]
(C) (1/2)BEC=C + BEH-H - 2BEC-H
(D) 2BEC-H - (1/2)BEC=C + BEH-H

25. What is the sign of DG° and the value of K for an electrochemical cell for which E°cell= 0.80 V?

 DK
(A)-> 1
(B)+> 1
(C)+< 1
(D)-< 1

26. The reaction between NO(g) and O2(g) is second order in NO(g) and first order in O2(g). By what factor will the reaction rate change if the concentrations of both reactants are doubled?

(A) 2
(B) 4
(C) 6
(D) 8

27. The decomposition of ethane into two methyl radicals has a first order rate constant of 5.5 x 10¯4 sec¯1 at 700 °C. What is the half-life for this decomposition in minutes?

(A) 9.1
(B) 15
(C) 21
(D) 30

28. The dependence of the rate constant or a reaction on temperature is given by the equation k = e-Ea / kT. Under what conditions is k the smallest?

(A) high T and large Ea
(B) high T and small Ea
(C) low T and large Ea
(D) low T and small Ea

29. The reaction CHCl3(g) + Cl2(g) ---> CCl4(g) + HCl(g) is believed to proceed by this mechanism:
Cl2(g) ---> 2Cl(g)fast
Cl(g) + CHCl3(g) ---> HCl(g) + CCl3(g)slow
CCl3(g) +Cl(g) ---> CCl4(g)fast

What rate equation is consistent with this mechanism?

(A) Rate = k [Cl2]
(B) Rate = k [Cl] [CHCl]
(C) Rate = k [Cl2] CHCl]
(D) Rate = k [Cl2]1/2 [CHCl3]

30. The activation energy of a certain reaction is 87 kJ mol¯1. What is the ratio of the rate constants for this reaction when the temperature is decreased from 37 °C to 15 °C?

(A) 5/1
(B) 8.3/1
(C) 13/1
(D) 24/1

P4(s) + 6 Cl2(g) <===> 4 PCl3(g)

31. Phosphorus reacts with chlorine as shown. What is the equilibrium constant expression, Kp, for this reaction?

(A) 4 PPCl3 / 6PPCl3 PCl2
(B) 4PPCl3 / 6PCl2
(C) PPCl3 / PP4 P6Cl2
(D) P4PCl3 / P6Cl2

32. The equilibrium constant for the reaction N2O4(g) <===> 2NO2(g) is 6.10 x 10¯3 at 25 °C. Calculate the value of K for this reaction: NO2(g) <===> (1/2)N2O4(g)

(A) 327
(B) 164
(C) 12.8
(D) 3.05 x 10¯3

33. The ion-product constant for water at 45 °C is 4.0 x 10¯14. What is the pH of pure water at this temperature?

(A) 6.7
(B) 7.0
(C) 7.3
(D) 13.4

34. The position of equilibrium lies to the right in each of these reactions

N2H5+ + NH3 <===> NH4+ + N2H4
NH3 + HBr <===> NH4+ + Br¯
N2H4 + HBr <===> N2H5+ + Br¯

Based on this information, what is the order of acid strength?

(A) HBr > N2H5+ > NH4+
(B) N2H5+ > N2H4 > NH4+
(C) NH3 > N2H4 > Br¯
(D) N2H5+ > HBr > NH4+

35. HCN is a weak acid (Ka = 6.2 x 10¯10). NH3 is a weak base (Kb = 1.8 x 10¯5). A 1.0 M solution of NH4CN would be

(A) strongly acidic
(B) weakly acidic
(C) neutral
(D) weakly basic

36. What is the percent ionization of a 0.010 M HCN solution? (Ka = 6.2 x 10¯10)

(A) 0.0025%
(B) 0.025%
(C) 0.25%
(D) 2.5%

37. How many moles of HCOONa must be added to 1.0 L of 0.10 M HCOOH to prepare a buffer solution with a pH of 3.4? (HCOOH Ka = 2 x 10¯4)

(A) 0.01
(B) 0.05
(C) 0.1
(D) 0.2

38. The acid-base indicator methyl red has a Ka of 1 x 10¯4. Its acidic form is red while its alkaline form is yellow. If methyl red is added to a colorless solution with a pH = 7, the color will be

(A) pink
(B) red
(C) orange
(D) yellow

39. Silver ions are added to a solution with [Br¯] = [Cl¯] = [CO32¯] = [AsO43¯] = 0.1M. Which compound will precipitate at the lowest [Ag+]?

(A) AgBr (Ksp = 5.0 x 10¯13)
(B) AgCl (Ksp = 1.8 10¯10)
(C) Ag2CO3 (Ksp = 8.1 x 10¯12)
(D) Ag3AsO4 (Ksp = 1.0 x 10¯22)

40. Consider a voltaic cell based on these half-cells.

Ag+(aq) + e¯ ---> Ag(s)E° = +0.80 V
Cd2+(aq) + 2e¯ ---> Cd(s)E° = -0.40 V

Identify the anode and give the voltage of this cell under standard conditions.

(A) Ag; Ecell = 0.40 V
(B) Ag; Ecell = 2.00 V
(C) Cd; Ecell = 1.20 V
(D) Cd; Ecell = 2.00 V

41. Which two species react spontaneously?

(A) Cu(s) + Ag+(aq)
(B) Br2(l) + Cl¯(aq)
(C) H2O(l) + Ca2+(aq)
(D) Au(s) + Mg2+(aq)

42. When the aluminum oxide is electrolyzed in the industrial process for the production of aluminum metal, aluminum is produced at one electrode and oxygen gas is produced at the other. For a given quantity of electricity, what is the ratio of moles of aluminum to moles of oxygen gas?

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

Questions 43 and 44 should be answered with reference to the reaction.

2Cr(s) +3Cu2+(aq) ---> 2Cr3+(aq) + 3Cu(s) E° = 0.43 V

43. Which expression gives the value for DG° in kJ mol¯1 for this reaction at 25°? (Please note that there is a negative sign in front of each answer.)

(A) - 6 x 8.31 x 0.43 x 1000
(B) (- 6 x 96500 x 0.43 x 1000) / 8.31
(C) (- 6 x 96500 x 0.43) / 1000
(D) (- 6 x 8.31 x 0.43) / 1000

44. What is the voltage for this cell when [Cu2+] = 1.0 M and [Cr3+] = 0.010 M?

(A) 1.2
(B) 0.87
(C) 0.47
(D) 0.39

45. All of these sets of quantum numbers are permissible except

  nlmlms
(A)100+1/2
(B)220-1/2
(C)311-1/2
(D)32-1+1/2

46. Which element can exhibit more than one oxidation state in compounds?

1. Cr
2. Pb
3. Sr
(A) 1 only
(B) 1 and 2 only
(C) 2 and 3 only
(D) 1,2 and 3

47. When the isoelectronic species, K+, Ca2+, and Cl¯, are arranged in order of increasing radius, what is the correct order?

(A) K+, Ca2+, Cl¯
(B) K+, Cl¯, Ca2+
(C) Cl¯, Ca2+, K+
(D) Ca2+, K+, Cl¯

48. Which Group 2 element has chemical properties least like the other members of the group?

(A) Be
(B) Ca
(C) Sr
(D) Ba

49. In the vapor state which atom has the largest ionization energy?

(A) Na
(B) K
(C) Mg
(D) Ca

50. All of these species have the same number of valence electrons as NO3¯ except

(A) CO32¯
(B) HCO3¯
(C) NF3
(D) SO3

51. Which set contains no ionic species?

(A) NH4Cl, OF2, H2S
(B) CO2, Cl2, CCl4
(C) BF3, AlF3, TlF3
(D) I2, CaO, CH3Cl

52. When these species are arranged in order of increasing bond energy, what is the correct sequenece?

(A) N2, O2, F2
(B) F2, O2, N2
(C) O2, F2, N2
(D) O2, N2, F2

53.The geometry of the atoms in the species PCl4+ is best described as

(A) tetrahedral
(B) see-saw
(C) square
(D) trigonal bipyramidal

54. Which are nonpolar molecules?

1. NCl3
2. SO3
3. PCl5
(A) 1 only
(B) 2 only
(C) 1 and 3 only
(D) 2 and 3 only

55. What are the hybridizations of carbon 1 and carbon 2 in the hydrocarbon? (Carbon 1 is the carbon farthest to the left and carbon 2 is the one boldfaced, the middle of the three carbons.)

CH3CHCH2

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

56. How many carbon-carbon bonds are in a molecule of 2-methyl-2-butanol?

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

57. Which molecule can exist as stereoisomers?

(A) CHF=CHF
(B) F2C=CCl2
(C) CH2F-CHF2
(D) CF3-CH3

58. What are the most likely products in the reaction between CH3CH2CH2OH and HI?

(A) CH3CH2CH2I and H2O
(B) CH3CH2CH3 and HOI
(C) CH3OH and CH3CH2I
(D) ICH2CH2CH2OH and H2

59. Addition polymers include

1. polyamide
2. polyethylene
3.polyester
(A) 1 only
(B) 2 only
(C) 2 and 3 only
(D) 1,2,and 3

60. All of these are aromatic compounds except

(A) hexene, C6H12
(B) toluene, C6H5CH3
(C) p-dichlorobenzene,C6H4Cl2
(D) naphthalene, C10H8