The 2021 USNCO Local Section Chemistry Olympiad Exam tests high school students on their knowledge of chemistry concepts and problem-solving skills. It includes 60 multiple-choice questions covering a wide range of topics, such as chemical reactions, stoichiometry, thermodynamics, and organic chemistry. Designed for students preparing for the National Chemistry Olympiad, this exam challenges participants with varying levels of difficulty. The exam also provides useful references, including a periodic table and constants, to assist students in their calculations and reasoning.

Key Points

  • Features 60 multiple-choice questions on various chemistry topics.
  • Covers areas such as stoichiometry, thermodynamics, and organic chemistry.
  • Includes a periodic table and constants for student reference.
  • Designed for high school students participating in the National Chemistry Olympiad.
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Property of ACS USNCO – Not for use as USNCO Local Section Exam after March 31, 2021
Distributed by the American Chemical Society, 1155 16
th
Street, N.W., Washington, DC 20036
All rights reserved. Printed in U.S.A.
2021 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)
James Dohm, Exxon-Mobil Corporation, Houston, TX
Xu Duan, Holton-Arms School, Bethesda, MD
Valerie Ferguson, Moore HS, Moore, OK
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 (retired)
John Kotz, State University of New York, Oneonta, NY (retired)
Sarah Leite, Hopkins School, New Haven, CT
Michael A. Morgan, Francisco Bravo Medical Magnet HS, Los Angeles, CA
Jane Nagurney, Scranton Preparatory School, Scranton, PA (retired)
Sheila Nguyen, Claremont Graduate University, Claremont, CA
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.
Page 2 Property of ACS USNCO – Not for use as USNCO Local Section Exam after March 31, 2021
ABBREVIATIONS AND SYMBOLS
CONSTANTS
amount of substance n
ampere A
atmosphere atm
atomic mass unit u
Avogadro constant N
A
Celsius temperature °C
centi– prefix c
coulomb C
density d
electromotive force E
energy of activation E
a
enthalpy H
entropy S
equilibrium constant K
Faraday constant F
free energy G
frequency ν
gas constant R
gram g
hour h
joule J
kelvin K
kilo– prefix k
liter L
measure of pressure mm Hg
milli– prefix m
molal m
molar M
molar mass M
mole mol
Planck’s constant h
pressure P
rate constant k
reaction quotient Q
second s
speed of light c
temperature, K T
time t
vapor pressure VP
volt V
volume V
year y
R = 8.314 J mol
–
1
K
–
1
R = 0.08314 L bar mol
–
1
K
–
1
F = 96,500 C mol
–
1
F = 96,500 J V
–1
mol
–
1
N
A
= 6.022 × 10
23
mol
–
1
h = 6.626 × 10
–34
J s
c = 2.998 × 10
8
m s
–
1
0 °C = 273.15 K
1 atm = 1.013 bar = 760 mm Hg
Specific heat capacity of H
2
O =
4.184 J g
–
1
K
–
1
EQUATIONS
o
ln
RT
EE Q
nF
= −
2
1 12
11
ln
a
E
k
k RT T

= −


1
PERIODIC TABLE OF THE ELEMENTS 18
1A 8A
1
H
1.008
2 13 14 15 16 17
2A 3A 4A 5A 6A 7A
2
He
4.003
3
Li
6.941
4
Be
9.012
5
B
10.81
6
C
12.01
7
N
14.01
8
O
16.00
9
F
19.00
10
Ne
20.18
11
Na
22.99
12
Mg
24.31
3
3B
4
4B
5
5B
6
6B
7
7B
8
8B
9
8B
10
8B
11
1B
12
2B
13
Al
26.98
14
Si
28.09
15
P
30.97
16
S
32.07
17
Cl
35.45
18
Ar
39.95
19
K
39.10
20
Ca
40.08
21
Sc
44.96
22
Ti
47.88
23
V
50.94
24
Cr
52.00
25
Mn
54.94
26
Fe
55.85
27
Co
58.93
28
Ni
58.69
29
Cu
63.55
30
Zn
65.39
31
Ga
69.72
32
Ge
72.61
33
As
74.92
34
Se
78.97
35
Br
79.90
36
Kr
83.80
37
Rb
85.47
38
Sr
87.62
39
Y
88.91
40
Zr
91.22
41
Nb
92.91
42
Mo
95.95
43
Tc
(98)
44
Ru
101.1
45
Rh
102.9
46
Pd
106.4
47
Ag
107.9
48
Cd
112.4
49
In
114.8
50
Sn
118.7
51
Sb
121.8
52
Te
127.6
53
I
126.9
54
Xe
131.3
55
Cs
132.9
56
Ba
137.3
57
La
138.9
72
Hf
178.5
73
Ta
180.9
74
W
183.8
75
Re
186.2
76
Os
190.2
77
Ir
192.2
78
Pt
195.1
79
Au
197.0
80
Hg
200.6
81
Tl
204.4
82
Pb
207.2
83
Bi
209.0
84
Po
(209)
85
At
(210)
86
Rn
(222)
87
Fr
(223)
88
Ra
(226)
89
Ac
(227)
104
Rf
(261)
105
Db
(262)
106
Sg
(263)
107
Bh
(262)
108
Hs
(265)
109
Mt
(266)
110
Ds
(281)
111
Rg
(272)
112
Cn
(285)
113
Nh
(286)
114
Fl
(289)
115
Mc
(289)
116
Lv
(293)
117
Ts
(294)
118
Og
(294)
58
Ce
140.1
59
Pr
140.9
60
Nd
144.2
61
Pm
(145)
62
Sm
150.4
63
Eu
152.0
64
Gd
157.3
65
Tb
158.9
66
Dy
162.5
67
Ho
164.9
68
Er
167.3
69
Tm
168.9
70
Yb
173.0
71
Lu
175.0
90
Th
232.0
91
Pa
231.0
92
U
238.0
93
Np
(237)
94
Pu
(244)
95
Am
(243)
96
Cm
(247)
97
Bk
(247)
98
Cf
(251)
99
Es
(252)
100
Fm
(257)
101
Md
(258)
102
No
(259)
103
Lr
(262)
Property of ACS USNCO – Not for use as USNCO Local Section Exam after March 31, 2021 Page 3
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.
At 120 °C and 1 atm pressure, 1.00 L of methane, CH
4
,
reacts completely with excess oxygen to form carbon
dioxide and water. What volumes of the two products are
produced at this pressure and temperature?
(A)
1.00 L CO
2
and 2.00 L H
2
O
(B)
1.00 L CO
2
and 4.00 L H
2
O
(C)
2.00 L CO
2
and 2.00 L H
2
O
(D)
2.00 L CO
2
and 4.00 L H
2
O
2.
Polypropylene is made by polymerizing propene, C
3
H
6
(M = 42.1). How many molecules of propene must be
polymerized to make 3.50 g polypropylene?
(A)
1.43 × 10
22
(B)
5.01 × 10
22
(C)
6.02 × 10
23
(D)
2.11 × 10
24
3.
An organic compound contains only carbon, hydrogen,
nitrogen, and oxygen. It is 61.71% C, 4.03% H, and
16.00% N by mass. What is its empirical formula?
(A)
C
5
H
4
NO
(B)
C
9
H
7
N
2
O
2
(C)
C
10
H
8
N
2
O
(D)
C
11
H
8
NO
2
4.
100.0 mL of 0.500 M CaBr
2
and 50.0 mL of 1.00 M
NaBr are mixed. What is the concentration of bromide
ion in the resulting solution?
(A)
0.500 M
(B)
0.667 M
(C)
0.750 M
(D)
1.00 M
5.
1.00 g of hydrated potassium carbonate, K
2
CO
3
•nH
2
O,
is heated to 250 °C to give 0.836 g anhydrous K
2
CO
3
.
What is the value of n?
(A)
0.16
(B)
1.0
(C)
1.5
(D)
2.0
6.
The concentration of an aqueous solution of a
nonvolatile, monoprotic acid is measured first by freezing
point depression and then by boiling point elevation. The
solution is found to be 0.93 m by freezing point
depression and to be 0.82 m by boiling point elevation.
Which is the best explanation for this discrepancy?
(A)
Ionization of the acid is markedly exothermic.
(B)
The solute associates partially into dimers at lower
temperatures.
(C)
The volume of the solution is greater at higher
temperatures.
(D)
The boiling point elevation constant for water is
smaller than its freezing point depression constant.
7.
When substances are separated by fractional distillation,
which property is least typical of the substance that
distills first?
(A)
Highest molar mass
(B)
Weakest intermolecular forces
(C)
Greatest vapor pressure
(D)
Lowest boiling point
8.
Which element is most abundant (by mass) in the Earth’s
crust?
(A)
Carbon
(B)
Oxygen
(C)
Magnesium
(D)
Silicon
9.
Which gas has the highest molar solubility in water at
25 °C and 1 atm?
(A)
CO
2
(B)
NH
3
(C)
O
2
(D)
H
2
S
10.
Which compound is colorless?
(A)
NaMnO
4
(B)
CrAsO
4
(C)
RbIO
4
(D)
BaCrO
4
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FAQs

What topics are covered in the 2021 USNCO Local Section Exam?
The 2021 USNCO Local Section Exam covers a comprehensive range of chemistry topics. These include stoichiometry, chemical reactions, thermodynamics, kinetics, equilibrium, and organic chemistry. Students are tested on their understanding of fundamental concepts as well as their ability to apply these concepts to solve complex problems. The exam is structured to assess both theoretical knowledge and practical problem-solving skills.
How is the 2021 USNCO Local Section Exam structured?
The exam consists of 60 multiple-choice questions, which are designed to evaluate students' chemistry knowledge and analytical skills. Each question has four answer choices, with only one correct option. The exam is timed, allowing students 110 minutes to complete it. This structure helps to simulate a competitive environment similar to that of the National Chemistry Olympiad.
What is the purpose of the USNCO Local Section Exam?
The USNCO Local Section Exam serves as a qualifying test for high school students interested in participating in the National Chemistry Olympiad. It aims to identify students with exceptional chemistry knowledge and problem-solving abilities. By participating in this exam, students can gain recognition for their skills and potentially advance to higher levels of competition, fostering interest in the field of chemistry.
What resources are provided during the exam?
Students are provided with a periodic table and a list of constants during the 2021 USNCO Local Section Exam. These resources are essential for performing calculations and understanding chemical principles. The inclusion of these references allows students to focus on problem-solving without needing to memorize all constants and values, thereby enhancing their performance.
Who is eligible to take the USNCO Local Section Exam?
The USNCO Local Section Exam is intended for high school students who have a strong interest in chemistry. Eligibility typically includes students enrolled in grades 9 through 12. Schools may have specific criteria for participation, and students are encouraged to prepare thoroughly to demonstrate their understanding of chemistry concepts and applications.

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