2022 U.S. NATIONAL CHEMISTRY OLYMPIAD - American Chemical Society

2022 U.S. NATIONAL

CHEMISTRY OLYMPIAD

NATIONAL EXAM PART II

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)

Jesse Bernstein, Miami Country Day School, Miami, FL (retired) Mark DeCamp, University of Michigan, Dearborn, MI (retired)

Joshua de Groot, College of Southern Idaho, Twin Falls, ID James Dohm, ExxonMobil, Houston, TX

Xu Duan, Holton-Arms School, Bethesda, MD

Valerie Ferguson, Moore HS, Moore, OK (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)

DIRECTIONS TO THE EXAMINER

All testing materials including scratch paper should be turned in and kept secure until May 14, 2022, after which tests can be returned to students and their teachers for further study.

When the student has completed Part II, or after one hour and forty-five minutes have elapsed, the student must turn in the Part II testing materials, and all scratch paper. Be sure that the student has supplied all of the information requested and that the same identification number used for Part I has been used again for Part II.

There are three parts to the National Olympiad Examination. You have the option of administering the three parts in any order, and you are free to schedule rest breaks between parts.

Part I Part II Part III

60 questions 8 questions 2 lab questions

single-answer multiple-choice problem-solving, explanations laboratory practical

1 hour, 30 minutes 1 hour, 45 minutes 1 hour, 30 minutes

A periodic table and other useful information are provided on page two for student reference.

Students should be permitted to use non-programmable calculators. 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.

DIRECTIONS TO THE EXAMINEE - DO NOT TURN THE PAGE UNTIL DIRECTED TO DO SO.

Part II requires complete responses to questions involving problem-solving and explanations. One hour and forty-five minutes are allowed to complete this part. Be sure to print your name, the name of your school, and your identification number in the spaces provided. (Be sure to use the same identification number you used for Part I.). Use separate sheets for scratch paper and do not attach your scratch paper to this examination. When you complete Part II (or at the end of one hour and forty-five minutes) you must turn in all testing materials and scratch paper.

Do not forget to turn in your U.S. citizenship/Green Card Holder statement before leaving the testing site today.

Property of ACS USNCO ? Not for use as USNCO National Exam after May 1, 2022 Distributed by the American Chemical Society, 1155 16th Street, N.W., Washington, DC 20036

All rights reserved. Printed in U.S.A.

ABBREVIATIONS AND SYMBOLS

amount of substance

n Faraday constant

F molar mass

M

ampere

A free energy

G mole

mol

atmosphere

atm frequency

Planck's constant

h

atomic mass unit

u gas constant

R pressure

P

Avogadro constant

NA gram

g rate constant

k

Celsius temperature

?C hour

h reaction quotient

Q

centi? prefix

c joule

J second

s

coulomb

C kelvin

K speed of light

c

density

d kilo? prefix

k temperature, K

T

electromotive force

E liter

L time

t

energy of activation

Ea measure of pressure mm Hg vapor pressure

VP

enthalpy

H milli? prefix

m volt

V

entropy

S molal

m volume

V

equilibrium constant

K molar

M year

y

CONSTANTS

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 NA = 6.022 ? 1023 mol?1 h = 6.626 ? 10?34 J s c = 2.998 ? 108 m s?1

0 ?C = 273.15 K 1 atm = 1.013 bar = 760 mm Hg Specific heat capacity of H2O =

4.184 J g?1 K?1

=E Eo - RT ln Q nF

EQUATIONS

= ln K

-H R

o

1 T

+

constant

ln= kk12

Ea R

1 T1

-

1 T2

1

PERIODIC TABLE OF THE ELEMENTS

18

1A

8A

1

2

H

2

1.008 2A

13 14 15 16 17 He 3A 4A 5A 6A 7A 4.003

3 4

5 6 7 8 9 10

Li Be

6.941 9.012

B

10.81

C

12.01

N

14.01

O

16.00

F

19.00

Ne

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 National Exam after May 1, 2022

Question 1 (page 1 of 1)

USNCO ID Number:

1. [11%] Compound A contains only carbon, fluorine, and chlorine. a. The vapor density of A at 1.00 bar and 25.0 ?C is 6.895 g L-1. What is the molar mass of A?

b. Chlorofluorocarbons such as A react with sodium metal to convert all the chlorine present into sodium chloride. The products from the reaction of sodium with 100.0 mL of gaseous A (at 1.00 bar and 25.0 ?C) are dissolved in water and a few drops of sodium chromate solution are added. This solution is then titrated with 0.3540 M AgNO3 solution until a bright red precipitate appears, which requires 22.79 mL of the titrant. How many chlorine atoms are there in a molecule of A?

c. What is the molecular formula of A? Justify your answer.

d. There is only one known isomer of A, compound B. The two compounds have nearly identical boiling points, but can be distinguished by 19F NMR spectroscopy, a technique that is sensitive to small differences in the chemical environments of fluorine atoms in compounds. When analyzed by this method, compound A exhibits only a single type of chemical environment for fluorine, while compound B shows two distinct environments for its fluorine atoms. Draw structural formulas for compounds A and B that are consistent with these observations.

Property of ACS USNCO ? Not for use as USNCO National Exam after May 1, 2022

Page 3

Question 2 (page 1 of 2)

USNCO ID Number:

2. [13%] A chemist prepares an ammonia/ammonium chloride buffer from solid ammonium chloride, 0.80 M NH3, and distilled water.

a. What is the pH of the 0.80 M NH3 solution? (The Ka of NH4+ is 5.6 ? 10-10.)

b. What mole ratio of ammonia to ammonium chloride is required for the buffer to have pH = 9.20?

c. Calculate the volume of ammonia solution and mass of ammonium chloride needed to make up 500 mL of the pH = 9.20 buffer with a total concentration of nitrogen-containing species (NH3 or NH4+) of 0.50 mol L-1.

Page 4

Property of ACS USNCO ? Not for use as USNCO National Exam after May 1, 2022

Question 2 (page 2 of 2)

USNCO ID Number:

d. To the solution described in (c) is added 10.0 mL of 0.10 M AgNO3.

i. Some AgCl precipitates from this mixture. Justify that this is the case. The Ksp of AgCl is 1.8 ? 10-10 and the Kf of Ag(NH3)2+ is 1.6 ? 107.

ii. What is the final concentration of free Ag+ in solution after this mixture achieves equilibrium?

iii. What is the mass of AgCl that precipitates from solution?

Property of ACS USNCO ? Not for use as USNCO National Exam after May 1, 2022

Page 5

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