U.S. National Chemistry Olympiad: 1998 National
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1. Which pair of substances could be separated by mixing with water and filtering?
(A) NaNO3 and K2SO4
(B) CH3OH and CH3COCH3
(C) MgCO3 and Fe(OH)3
(D) KCl and CuS
2. Which gas produces an acidic solution when bubbled into water?
3. A dilute HCl solution is to be prepared from a more concentrated solution. Which of
pieces of glassware will give the highest level of precision?
(A) graduated cylinder and volumetric flask
(B) two graduated cylinders
(C) pipet and graduated cylinder
(D) pipet and volumetric flask
4. Which substance is likely to show the greatest change in mass when exposed to air?
5. Which is a yellow solid?
6. An alloy of gold and silver contains 38.5% silver by mass and has a density of 14.6
g mL¯1. What is the molar concentration of silver in this alloy?
(A) 52.1 mol L¯1
(B) 45.6 mol L¯1
(C) 3.57 mol L¯1
(D) 2.64 mol L¯1
7. As2S3 reacts with O2 to give SO2 and As2O3.
What is the smallest whole number coefficient for O2 when the equation for this
reaction is balanced correctly?
_As2S3(s) + _O2(g) ---> _As2O3(s)
8. A 0.242 g sample of potassium is heated in oxygen. The result is 0.440 g of a
crystalline compound. What is the formula of this compound?
9. What volume of 3.0 M Na2SO4 must be added to 25 mL of 1.0 M
BaCl2 to produce 5.0 g of BaSO4?
(A) 7.2 mL
(B) 8.3 mL
(C) 10.0 mL
(D) 14 mL
10. These three equations describe an oxidation-reduction method for determining
dissolved oxygen in water. How many moles of S2O32¯ are
equivalent of each mole of O2?
1) 2Mn2+(aq) + 4OH¯(aq) + O2(g) ---> 2MnO2(s) + 2H2O(l)
2) MnO2(s) + 2I¯(aq) + 4H+(aq) ---> Mn2+(aq) + I2(aq)
3) 2S2O32¯(aq) + I2(aq) ---> S4O62¯(aq)
11. A 15 mL sample of 0.20 M MgCl2 is added to 45 mL of 0.40 M AlCl3.
What is the molarity of Cl¯ ions in the final solution?
(A) 1.0 M
(B) 0.60 M
(D) 0.30 M
12. How many electrons are present in 2.0 x 10¯3 moles of 188O2¯?
(A) 1.2 x 1021
(B) 9.6 x 1021
(C) 1.2 x 1022
(D) 1.9 x 1022
13. In which change of state are covalent bonds broken?
(A) evaporation of water
(B) fusion of sodium chloride
(C) vaporization of diamond
(D) sublimation of dry ice
14. By what factor does the average velocity of a gaseous molecule increase when the
absolute temperature is doubled?
15. Which species is expected to have the highest boiling point at 1 am pressure?
16. What is the vapor pressure of a solution with a benzene to octane molar ratio of
|Vapor Pressure at 50 °C
(A) 120 mmHg
(B) 320 mmHg
(C) 400 mmHg
(D) 680 mmHg
17. Which halogen in its standard state has the greatest absolute entropy per mole?
18. Which combination of vapor pressure, intermolecular forces and DHvaporization
is matched correctly?
19. Calculate DH° for this reaction.
C2H2(g) + 2H2(g) ---> C2H6(g)
DHcombustion, kJ mol¯1
(A) -312 kJ
(B) -26 kJ
(C) +26 kJ
(D) +312 kJ
20. For which process would DS° be expected to have the
greatest positive value?
(A) O2(g) + 2H2(g) ---> 2H2O(g)
(B) H2O(s) ---> H2O(l)
(C) H2(g) + I2(g) ---> 2HI(g)
(D) N2O4(g) ---> 2NO2(g)
21. (1/2) N2(g)+ (3/2) H2(g) ---> NH3(g)
For this reaction at 25 °C, DG°f is -16.5 kJ
mol¯1. What is the equilibrium constant, Keq, for this reaction at
(B) 7.80 x 102
(C) 4.57 x 106
(D) 2.98 x 1034
22. What are the signs for DH, DS,
and DG for the freezing of liquid water at -10 °C?
23. Which of these factors affect the value of the specific rate constant for the
reaction 2A(g) ---> B(g)?
(A) I, II, and III
(B) I and II only
(C) II and III only
(D) III only
24. Which statement about work and heat is true?
(A) A given quantity of heat can be completely converted to work.
(B) Heat and work are both state functions.
(C) Some heat is always produced when work is done.
(D) Work is a state function, whereas heat is not.
25. The reaction between KMnO4 and H2C2O4
can be followed by monitoring the disappearance of the purple color of the MnO4¯
ion. These data were obtained for the reaction carried out at a constant temperature of 25
of MnO4¯ (aq), M s¯1
1.08 x 10¯2 M
5.4 x 10¯5
1.08 x 10¯2 M
1.1 x 10¯4
2.17 x 10¯2 M
2.1 x 10¯4
Specify the order of this reaction with respect to [MnO4¯]
26. For which reaction order is the half-life independent of the initial concentration?
I first order
II second order
(A) I only
(B) II only
(C) both I and II
(D) neither I nor II
27. What is the activation energy for the reverse of this reaction?
N2O4(g) ---> 2NO2(g)
Data for the given reaction is: DH = + 54.0 kJ and Ea
= +57.2 kJ.
(A) -54.0 kJ
(B) +3.2 kJ
(C) +60.2 kJ
(D) +111.2 kJ
28. How does an increase in temperature affect the rates of the foward and reverse
reactions for an exothermic reaction?
||rate of foward reaction
||rate of reverse reaction
||remains the same
29. The reaction between chloroform, CHCl3(g), and chlorine, Cl2(g),
to form CCl4(g) and HCl(g) is believed to occur by this series of steps.
Step 1 Cl2 ---> Cl(g) + Cl(g)
Step 2 CHCl3(g) + Cl(g) ---> CCl3(g) + HCl(g)
Step 3 CCl3(g) + Cl(g) ---> CCl4(g)
If this reaction is first order in CHCl3 and half order in Cl2,
which statement about the relative rates of step 1, 2, and 3 is correct?
(A) Step 1 is the slowest.
(B) Steps 1 and 2 must both be slow.
(C) Step 2 must be slower than step 1.
(D) Step 3 must be the slowest
30. This reaction occurs readily above 500 °C.
2HgO(s) ---> 2Hg(l) + O2(g)
What is the equilibrium for this reaction?
(A) K = [Hg]2[O2] / [HgO]2
(B) K = [Hg][O2] / [HgO]
(C) K = [Hg]2[O2]
(D) K = [O2]
31. Consider this equilibrium, for which DH < 0.
HgO(s) + 4I¯(aq) + H2O(l) <===> HgI42¯
Which changes will increase the equilbrium concentration of HgI42¯?
I Increasing the mass of HgO(s) present
II Increasing [I¯]
III Adding 1 M HCI
(A) I only
(B) II only
(C) II and III only
(D) I, II, and III
32. The equilibrium constant for this reaction is approximately 10¯3.
HPO42¯(aq) + HCO3¯(aq) <===> H2PO4¯(aq)
Which is the strongest conjugate base in this reaction?
33. A weak acid, HX, has Ka = 9.0 x 10¯6. Within which range
does the percent dissociation for a 0.01 M HX solution lie?
(A) between 1.0% and 10%
(B) between 0.10% and 1.0%
(C) between 0.01% and 0.10%
(D) less than 0.01%
34. Which salt dissolves in water to produce a solution with a pH < 7?
35. Which mixture forms a buffer when dissolved in 1.0 L of water?
(A) 0.2 mol NaOH + 0.2 mol HBr
(B) 0.2 mol NaCl + 0.3 mol HCl
(C) 0.4 mol HNO2 + 0.2 mol NaOH
(D) 0.5 mol NH3 + 0.5 mol HCl
36. The equilibrium constant for this reaction is 3.6 x 10¯7
OCl¯(aq) + H2O(l) <===> HOCl(aq) + OH¯(aq)
What is Ka for HOCl?
(A) 2.8 x 10¯8
(B) 3.6 x 10¯7
(C) 6.0 x 10¯4
(D) 2.8 x 106
37. For which titration would the use of phenophthalein introduce a significant error?
Kindicator for phenolphthalein = 1 x 10¯9
38. When solid lead iodide is added to water, the equilibrium concentration of I¯
becomes 2.6 x 10¯3 M. What is the Ksp for PbI2?
(A) 2.2 x 10¯9
(B) 8.8 x10¯9
(C) 1.8 x 10¯8
(D) 3.5 x 10¯8
39. When these standard half reactions are combined to give a
spontaneous reaction in a voltaic cell, what is the cell voltage?
|Standard Reduction Potentials,
Sn2+(aq) + 2e¯ ---> Sn(s)
Ag+(aq) + e¯ ---> Ag(s)
(A) 1.74 V
(B) 1.46 V
(C) 0.94 V
(D) 0.66 V
40. How many moles of elections are transferred when this equation is balanced with the
smallest whole number coefficients?
_IO3¯ + _H2O2 + _H+ --->
_I2 + _O2 + _H2O
41. If the E°cell for a given reaction has a negative value, which gives
the correct relationships for the values of DG° and Keq?
A. DG° > 0; Keq < 1
B. DG° > 0; Keq > 1
C. DG° < 0; Keq > 1
D. DG° < 0; Keq < 1
42. When anions undergo oxidation, they move toward the
A. anode of a voltaic cell and the cathode of an electrolytic cell
B. cathode of a voltaic cell and the anode of an electrolytic cell
C. anodes of both types of cells
D. cathodes of both types of cells
43. How much time is required to produce 0.10 mol of chlorine gas during the
electrolysis of molten sodium chloride using a current of 3.0 amps?
A. 55 min
B. 110 min
C. 220 min
D. 330 min
44. The visible spectrum of the hydrogen atom consists of a series of lines that
A. converge at low energies.
B. converge at high energies.
C. are separated by equal energies.
D. are randomly spaced.
45. When the elements C, N and Si are arranged in order of increasing first ionization
energy, which is the correct order?
A. C < N < Si
B. N < C < Si
C. Si < C < N
D. Si < N < C
46. Which is a possible set of quantum numbers for a valence electron in ground state
atom of phosphorus?
47. These are the first eight ionization energies for a particular
neutral atom. All values are expressed in MJ mol¯1. How many valence electrons
does this atom possess?
48. Which gaseous ion in its ground state has the greatest number of unpaired
49. Which of these characteristics describe the PCl3 molecule?
I trigonal planar shape
II sp3 hybridized phosphorus atom
III polar bonds
IV nonpolar molecule
A. I and II only
B. II and III only
C. I and IV only
D. I, III, and IV only
50. According to the Lewis structure for the HNNH, how many sigma bonds, pi bonds, and
lone pairs of electrons are present?
||lone pairs of electrons
51. In the Lewis structure for the BrF4¯ ion, how many lone pairs of
electrons are placed around the central atom?
52. What term is used for the measure of an atom's attraction for the electrons that
constitute a covalent bond?
(A) ionization energy
(B) bond dissociation energy
(C) electron affinity
53. One way of writing the Lewis structure of the cyanate ion, OCN¯, places one double
bond between the carbon atom and the oxygen atom and another double bond between the
carbon atom and the nitrogen atom. What are the formal charges on the oxygen, carbon, and
nitrogen atoms, respectively for this structure?
(A) 0, 0, -1
(B) -1, 0, 0
(C) -1, +1, -1
(C) -2, 1, 0
54. Lithium crystallizes in a body-centered cubic unit cell. What is the mass of one
unit cell? Report your answer in grams.
(A) 1.15 x 10¯23 g
(B) 2.30 x 10¯23 g
(C) 5.75 x 10¯23 g
(D) 1.04 x 10¯22 g
55. Which compound is an isomer of 2-methylbutane?
56. How many different isomers have the molecular formula C3H6Cl2?
57. Which type of compound is most likely to be colored?
58. A certain four-carbon alcohol reacts with acidified potassium dichromate to form a
ketone. Which structure is most likely for that four-carbon alcohol?
59. What type of compound is CH3CH2OCH3?
60. Which pair are two different names for the same compound?
(A) acetic acid and ethanoic acid
(B) formaldehyde and methanol
(C) isopropyl alcohol and 1-propanol
(D) ethene and ethyne