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2020 U.S. NATIONAL
CHEMISTRY OLYMPIAD
LOCAL SECTION EXAM
Prepared by the American Chemical Society Chemistry Olympiad Examinations Task Force
OLYMPIAD EXAMINATIONS TASK FORCE
Seth N. Brown, Chair, University of Notre Dame, Notre Dame, IN
James Ayers, Colorado Mesa University, Grand Junction, CO
Jerry Bell, Simmons University, Boston, MA (retired)
Mark DeCamp, University of Michigan, Dearborn, MI (retired)
Joshua de Groot, College of Southern Idaho, Twin Falls, ID
James Dohm, Vanderbilt University, Nashville, TN
Xu Duan, Holton-Arms School, Bethesda, MD
Valerie Ferguson, Moore HS, Moore, OK (retired)
Julie Furstenau, Thomas B. Doherty HS, Colorado Springs, CO (retired)
Kimberly Gardner, United States Air Force Academy, CO
Paul Groves, South Pasadena HS, South Pasadena, CA
Nicolas Hamel, Clackamas Community College, Oregon City, OR
David W. Hostage, Taft School, Watertown, CT
John Kotz, State University of New York, Oneonta, NY (retired)
Michael A. Morgan, Francisco Bravo Medical Magnet HS, Los Angeles, CA
Jane Nagurney, Scranton Preparatory School, Scranton, PA (retired)
DIRECTIONS TO THE EXAMINER
This test is designed to be taken with an answer sheet on which the student records his or her responses. All answers are to be marked
on that sheet, not written in the booklet. Each student should be provided with an answer sheet and scratch paper, both of which must
be turned in with the test booklet at the end of the examination. Local Sections may use an answer sheet of their own choice.
The full examination consists of 60 multiple-choice questions representing a fairly wide range of difficulty. A periodic table and other
useful information are provided on page two of this exam booklet for student reference.
Only non-programmable calculators are to be used on the ACS Local Section exam. The use of a programmable calculator, cell phone,
or any other device that can access the internet or make copies or photographs during the exam is grounds for disqualification.
Suggested Time: 60 questions—110 minutes
DIRECTIONS TO THE EXAMINEE
DO NOT TURN THE PAGE UNTIL DIRECTED TO DO SO.
This is a multiple-choice examination with four choices for each question. There is only one correct or best answer to each question.
When you select your choice, blacken the corresponding space on the answer sheet with your pencil. Make a heavy full mark, but no
stray marks. If you decide to change your answer, be certain to erase your original answer completely.
Property of ACS USNCO – Not for use as USNCO Local Section Exam after March 31, 2020
th
Distributed by the American Chemical Society, 1155 16 Street, N.W., Washington, DC 20036
All rights reserved. Printed in U.S.A.
ABBREVIATIONS AND SYMBOLS CONSTANTS
amount of substance n Faraday constant F molar mass M 1 1
ampere A free energy G mole mol R = 8.314 J mol– K–
1 1
atmosphere atm frequency ν Planck’s constant h R = 0.08314 L bar mol– K–
1
atomic mass unit u gas constant R pressure P F = 96,500 C mol–
Avogadro constant N rate constant k
A gram g 1
Celsius temperature °C hour h reaction quotient Q F = 96,500 J V–1 mol–
1
23 –
N = 6.022 × 10 mol
centi– prefix c joule J second s A
coulomb C kelvin K speed of light c –34
density d kilo– prefix k temperature, K T h = 6.626 × 10 J s
1
8 –
electromotive force E liter L time t c = 2.998 × 10 m s
energy of activation Ea measure of pressure mm Hg vapor pressure VP 0 °C = 273.15 K
enthalpy H milli– prefix m volt V 1 atm = 1.013 bar = 760 mm Hg
entropy S molal m volume V Specific heat capacity of H O =
equilibrium constant K molar M 2
1 1
– –
4.184 J g K
EQUATIONS
o RT o
−∆H 1 k E 11
2 a
EE= −lnQ ln K =+constant ln = −
nF k RTT
RT
1 12
1 PERIODIC TABLE OF THE ELEMENTS 18
1A 8A
1 2
H 2 13 14 15 16 17 He
1.008 2A 3A 4A 5A 6A 7A 4.003
3 4 5 6 7 8 9 10
Li Be B C N O F Ne
6.941 9.012 10.81 12.01 14.01 16.00 19.00 20.18
11 12 13 14 15 16 17 18
Na Mg 3 4 5 6 7 8 9 10 11 12 Al Si P S Cl Ar
22.99 24.31 3B 4B 5B 6B 7B 8B 8B 8B 1B 2B 26.98 28.09 30.97 32.07 35.45 39.95
19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36
K Ca Sc Ti V Cr Mn Fe Co Ni Cu Zn Ga Ge As Se Br Kr
39.10 40.08 44.96 47.88 50.94 52.00 54.94 55.85 58.93 58.69 63.55 65.39 69.72 72.61 74.92 78.97 79.90 83.80
37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54
Rb Sr Y Zr Nb Mo Tc Ru Rh Pd Ag Cd In Sn Sb Te I Xe
85.47 87.62 88.91 91.22 92.91 95.95 (98) 101.1 102.9 106.4 107.9 112.4 114.8 118.7 121.8 127.6 126.9 131.3
55 56 57 72 73 74 75 76 77 78 79 80 81 82 83 84 85 86
Cs Ba La Hf Ta W Re Os Ir Pt Au Hg Tl Pb Bi Po At Rn
132.9 137.3 138.9 178.5 180.9 183.8 186.2 190.2 192.2 195.1 197.0 200.6 204.4 207.2 209.0 (209) (210) (222)
87 88 89 104 105 106 107 108 109 110 111 112 113 114 115 116 117 118
Fr Ra Ac Rf Db Sg Bh Hs Mt Ds Rg Cn Nh Fl Mc Lv Ts Og
(223) (226) (227) (261) (262) (263) (262) (265) (266) (281) (272) (285) (286) (289) (289) (293) (294) (294)
58 59 60 61 62 63 64 65 66 67 68 69 70 71
Ce Pr Nd Pm Sm Eu Gd Tb Dy Ho Er Tm Yb Lu
140.1 140.9 144.2 (145) 150.4 152.0 157.3 158.9 162.5 164.9 167.3 168.9 173.0 175.0
90 91 92 93 94 95 96 97 98 99 100 101 102 103
Th Pa U Np Pu Am Cm Bk Cf Es Fm Md No Lr
232.0 231.0 238.0 (237) (244) (243) (247) (247) (251) (252) (257) (258) (259) (262)
Page 2 Property of ACS USNCO – Not for use as USNCO Local Section Exam after March 31, 2020
DIRECTIONS
When you have selected your answer to each question, blacken the corresponding space on the answer sheet using a soft, #2
pencil. Make a heavy, full mark, but no stray marks. If you decide to change an answer, erase the unwanted mark very carefully.
There is only one correct answer to each question. Any questions for which more than one response has been blackened will not
be counted.
Your score is based solely on the number of questions you answer correctly. It is to your advantage to answer every question.
1. A 2.50 L sample of butane gas (C H ), measured at 22.0 8. A student is using a buret for a titration. What initial
4 10
ºC and 1.20 atm pressure, is combusted completely and buret reading should be recorded?
the carbon dioxide gas collected at the same pressure and
temperature. What volume of CO is produced?
2
(A) 2.50 L (B) 9.00 L
(C) 10.0 L (D) 22.5 L
2. How many hydrogen atoms are in 2.50 g of pharmacolite, (A) 6.6 mL (B) 7.4 mL
CaHAsO4•2H2O (M = 216.0)?
(A) 21 (B) 22 (C) 6.63 mL (D) 7.37 mL
6.97 × 10 2.09 × 10
(C) 22 (D) 22
2.79 × 10 3.48 × 10 9. A strip of metallic zinc is placed in a beaker containing
dilute aqueous copper(II) nitrate. Which statement
3. Methanol is produced industrially by catalytic correctly describes what takes place?
hydrogenation of carbon monoxide according to the (A) No reaction takes place.
following equation:
CO(g) + 2 H (g) → CH OH(l) (B) The mass of the metal strip decreases as the zinc is
2 3 oxidized.
If the yield of the reaction is 40%, what volume of CO (C) A white precipitate of CuNO is formed.
(measured at STP) would be needed to produce 1.0 × 106 3
kg CH3OH? (D) Bubbles of NO(g) form as the nitrate ion is reduced.
(A) 8 (B) 8
2.8 × 10 L 7.0 × 10 L 10. Which element does NOT have multiple allotropes?
(C) 9 (D) 9
1.7 × 10 L 2.1 × 10 L (A) Carbon (B) Oxygen
(C) Fluorine (D) Phosphorus
4. What volume of 18.0 M sulfuric acid must be diluted to
250.0 mL to afford a 0.55 M solution of sulfuric acid? 11. Which reaction is not exothermic?
(A) 3.1 mL (B) 4.5 mL (C) 7.6 mL (D) 31 mL (A) Dilution of concentrated hydrochloric acid in water.
5. What is the concentration of H O in a solution that is
2 2 (B) Dilution of concentrated sulfuric acid in water.
30.0% by mass hydrogen peroxide and has a density of
-3 (C) Dissolution of solid sodium hydroxide in water.
1.11 g cm ?
(A) 9.79 M (B) 12.6 M (D) Dissolution of solid sodium bicarbonate in water.
(C) 18.5 M (D) 32.6 M
6. A 5.00 g mixture of potassium sulfide and potassium
chloride contains 2.80 g potassium. What percentage by
mass of the mixture is potassium sulfide?
(A) 13.8% (B) 19.2% (C) 44.0% (D) 96.1%
7. Which salt dissolves in water to give a pink solution?
(A) Co(CH COO) (B) CuSO
3 2 4
(C) Fe(NO ) (D) ZnCl
3 3 2
Property of ACS USNCO – Not for use as USNCO Local Section Exam after March 31, 2020 Page 3
12. The molar mass of a volatile organic liquid is measured 16. In which are the ionic compounds listed in order of
by weighing the mass of an empty flask of known increasing magnitude of their lattice energy?
volume, adding some of the liquid, heating the flask in a (A) CaO < RbI < LiF < LiI
water bath until the liquid has just vaporized completely, (B) RbI < CaO < LiI < LiF
then sealing the flask, letting it cool, and remeasuring the
mass of the flask with the remaining organic compound. (C) LiI < LiF < CaO < RbI
Which error will lead to a calculated value of the molar
mass that is lower than the theoretical value? (D) RbI < LiI < LiF < CaO
(A) The flask is not sealed promptly after the last of the
compound vaporizes.
17. Sodium halides crystallize in the rock salt structure,
(B) The organic compound dimerizes to an appreciable which has a cubic unit cell with four formula units per
-3
extent in the gas phase. unit cell. A sodium halide has a density of 2.83 g cm
(C) The barometric pressure was assumed to be 1 atm and a unit cell edge length of 462 pm. Which compound
but in fact was greater than 1 atm. is it?
(D) The volume of the flask used in the calculation is (A) NaF (B) NaCl (C) NaBr (D) NaI
smaller than the true volume.
18. The tetragonal unit cell of white tin is shown below.
13. Which gas has an effusion rate closest to half that of Each circle represents a tin atom, with the gray circles
oxygen gas at a given temperature? sitting on the four vertical faces of the unit cell. How
many tin atoms are contained in this unit cell?
(A) H (B) He (C) SO (D) Xe
2 2
14. Which compound has the highest normal boiling point?
(A) 1-butanol, CH CH CH CH OH
3 2 2 2
(B) 2-butanol, CH CH CH(CH )OH
3 2 3
(C) 2-methyl-1-propanol, (CH ) CHCH OH
3 2 2 (A) 2 (B) 4 (C) 8 (D) 13
(D) 2-methyl-2-propanol, (CH ) COH
3 3 19. For which reaction is ∆Hº equal to ∆Hº of CaSO (s)?
rxn f 3
15. A portion of the phase diagram of elemental sulfur is (A) 1 3
Ca(s) + / S (s) + / O (g) → CaSO (s)
shown below. Which statement about sulfur is correct? 8 8 2 2 3
(B) 8 Ca(s) + S (s) + 12 O (g) → 8 CaSO (s)
8 2 3
(C) 8 Ca(s) + S (g) + 12 O (g) → 8 CaSO (s)
8 2 3
(D) CaO(s) + SO (g) → CaSO (s)
2 3
20. A 2.00 g sample of ice at 0.0 ºC is placed in 50.0 g of
water initially at 25.0 °C in an insulated container. What
is the final temperature after the system has achieved
-1
equilibrium? (For ice, ΔHºfusion = 6.01 kJ mol .)
(A) 21.0 ºC (B) 21.8 ºC
(C) 22.5 ºC (D) 24.0 ºC
(A) Rhombic sulfur cannot be sublimed without first
converting to monoclinic sulfur. 21. Ethanol has a normal boiling point of 78.3 ºC and a
-1
(B) The conversion of rhombic sulfur to monoclinic standard heat of vaporization (ΔHºvap) of 38.6 kJ mol .
sulfur is exothermic. What is the vapor pressure of ethanol at 45.0 ºC?
(C) Rhombic sulfur is denser than monoclinic sulfur. (A) 0.25 atm (B) 0.57 atm
(D) At atmospheric pressure, monoclinic sulfur cannot (C) 0.87 atm (D) 0.91 atm
be in equilibrium with liquid sulfur.
Page 4 Property of ACS USNCO – Not for use as USNCO Local Section Exam after March 31, 2020
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