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Property of ACS USNCO – Not for use as USNCO Local Section Exam after March 31, 2022 Distributed by the American Chemical Society, 1155 16 th^ Street, N.W., Washington, DC 20036 All rights reserved. Printed in U.S.A.
2022 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)
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
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, 2022
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
R = 8.314 J mol–1^ K – R = 0.08314 L bar mol –1^ K – F = 96,500 C mol– F = 96,500 J V –1^ mol– N A = 6.022 × 10 23 mol– h = 6.626 × 10 –34^ J s c = 2.998 × 10 8 m s– 0 °C = 273.15 K 1 atm = 1.013 bar = 760 mm Hg Specific heat capacity of H2O = 4.184 J g –1^ K –
EQUATIONS
E E^ o^^ RT ln Q nF
= −
o 1 ln constant
H
K
R T
^
2 1 1 2
ln a k E k R T T
=^ −
1 PERIODIC TABLE OF THE ELEMENTS 18 1A 8A 1 H
2A 3A 4A 5A 6A 7A
He
3 Li
Be
B
C
N
O
F
Ne
11 Na
Mg
3B
4B
5B
6B
7B
8B
8B
8B
1B
2B
Al
Si
P
S
Cl
Ar
19 K
Ca
Sc
Ti
V
Cr
Mn
Fe
Co
Ni
Cu
Zn
Ga
Ge
As
Se
Br
Kr
37 Rb
Sr
Y
Zr
Nb
Mo
Tc ( 98 )
Ru
Rh
Pd
Ag
Cd
In
Sn
Sb
Te
I
Xe
55 Cs
Ba
La
Hf
Ta
W
Re
Os
Ir
Pt
Au
Hg
Tl
Pb
Bi
Po ( 209 )
At ( 210 )
Rn ( 222 ) 87 Fr ( 223 )
Ra ( 226 )
Ac ( 227 )
Rf ( 261 )
Db ( 262 )
Sg ( 263 )
Bh ( 262 )
Hs ( 265 )
Mt ( 266 )
Ds ( 281 )
Rg ( 272 )
Cn (285)
Nh (286)
Fl (289)
Mc (289)
Lv (293)
Ts (294)
Og (294)
58 Ce
Pr
Nd
Pm ( 145 )
Sm
Eu
Gd
Tb
Dy
Ho
Er
Tm
Yb
Lu
90 Th
Pa
U
Np ( 237 )
Pu ( 244 )
Am ( 243 )
Cm ( 247 )
Bk ( 247 )
Cf ( 251 )
Es ( 252 )
Fm ( 257 )
Md ( 258 )
No ( 259 )
Lr (262)
Page 4 Property of ACS USNCO – Not for use as USNCO Local Section Exam after March 31, 2022
11. Which liquid will NOT react with metallic sodium? (A) Water (B) Mineral oil (C) Ethanol (D) Carbon tetrachloride
12. The molar enthalpy of solution of a salt that dissolves endothermically in water is measured in a coffee-cup calorimeter by weighing a known amount of distilled water into the cup and measuring its temperature, then adding a known mass of the salt to the water and measuring the temperature after the salt dissolves. If some water is initially present in the cup before the weighed amount of water is added, what is the effect on the experiment? (A) Calculated ∆ H °soln > True ∆ H °soln (B) Calculated ∆ H °soln = True ∆ H °soln (C) Calculated ∆ H °soln < True ∆ H °soln (D) The reaction will be calculated to be exothermic even though it is actually endothermic. 13. When liquid water converts to solid ice at 0 °C and 1 atm pressure, which of the following changes takes place? (A) Heat flows out of the system. (B) The volume of the system decreases. (C) The vapor pressure of water increases. (D) The hydrogen bonds become weaker. 14. Which isomer of C 4 H 8 O 2 has the greatest solubility in water? (A) (B)
(C) (D)
15. Which compound has the lowest normal boiling point? (A) HF (B) HCl (C) HBr (D) HI 16. A sealed container contains a gaseous sample at 300.0 K consisting of either pure ethane (C2H 6 ), pure neon (Ne), or a mixture of the two. The pressure inside the container at this temperature is 1.00 atm. When the container is cooled to 150.0 K, the pressure is 0.37 atm. What is the composition of the sample? (The vapor pressure of C2H (^6) at 150 K is 0.10 atm; the critical temperature of Ne is 44 K.) (A) Pure ethane (B) Pure neon (C) A mixture of ethane and neon. (D) It cannot be determined from the information given. 17. Which statement about sulfur, whose phase diagram is shown below, is correct?
(A) Monoclinic sulfur sublimes at 1 atm pressure while rhombic sulfur does not. (B) Rhombic sulfur is less dense than monoclinic sulfur. (C) At temperatures above 119 °C, monoclinic sulfur cannot exist at equilibrium. (D) The conversion of rhombic sulfur to monoclinic sulfur is endothermic.
18. Aluminum crystallizes in a face-centered cubic unit cell with an edge length of 405 pm. What is its density? (A) 0.674 g cm-3^ (B) 1.35 g cm - (C) 2.70 g cm -3^ (D) 5.40 g cm - 19. A container with 100.0 g of ice at 0 °C is placed in a humid room whose temperature is 40 °C. The ice melts as water vapor condenses into the container. Assuming that all the heat transferred to the container comes from condensation, how much water will have condensed in the container once all the ice is melted and has reached 40 °C? The heat of fusion of ice is 334 J g -1^ and the heat of vaporization of water is 2260 J g -^. (A) 13.8 g (B) 14.8 g (C) 22.2 g (D) 677 g 20. The standard enthalpy of formation of hematite, Fe2O (^) 3( s ), is –825.5 kJ mol-1^. What is the standard enthalpy of reaction for the reduction of hematite with carbon monoxide to give metallic iron as shown below?
CO( g ) + 1 / 2 O (^) 2( g ) → CO 2( g )
∆ H °rxn = –283.0 kJ mol-
Fe (^) 2O (^) 3( s ) + 3 CO( g ) → 2 Fe( s ) + 3 CO 2 ( g )
∆ H °rxn = ???
(A) –23.5 kJ mol-1^ (B) –542.5 kJ mol- (C) –849.0 kJ mol-1^ (D) –1674.5 kJ mol-
Property of ACS USNCO – Not for use as USNCO Local Section Exam after March 31, 2022 Page 5
21. Which of the following equations correctly describe the change in internal energy, Δ E , of a reaction taking place in a bomb calorimeter? I. ∆ E = q II. ∆ E = ∆ H – V ∆ P (A) I only (B) II only (C) Both I and II (D) Neither I nor II
22. Cyclopropane isomerizes exothermically to propene as shown.
The C–C single bond in propene has an estimated bond dissociation enthalpy (BDE) of 345 kJ mol-1^ , while the C=C double bond in propene has a BDE of 611 kJ mol-^. Assuming that the C–H bonds in propene and cyclopropane all have the same BDE, what is the estimated BDE of a C–C single bond in cyclopropane? (A) 308 kJ mol-1^ (B) 329 kJ mol- (C) 423 kJ mol-1^ (D) 924 kJ mol-
23. Two reactions have similar ∆ H °rxn values (∆ H °rxn (1) ≈ ∆ H °rxn (2) ), but reaction (1) has a much smaller standard entropy change than reaction (2) (∆ S °rxn (1) << ∆ S °rxn (2) ). At 298 K, which statements about these two reactions must be correct? I. Reaction (1) must have a larger equilibrium constant ( K eq (1) > K eq (2) ). II. Reaction (1) must have a larger Arrhenius prefactor ( A (1) > A (2) ). (A) I only (B) II only (C) Both I and II (D) Neither I nor II 24. Which reaction has ∆ S °rxn > 0? All reactants and products are liquids. (A)
(B)
(C)
(D)
25. Dichromate ion is reduced by chloride ion according to the equation below. If [Cl–] is decreasing at a rate of 0. mol L -1^ min -1^ , how is the concentration of Cr 3+( aq ) changing? 14 H +( aq ) + Cr 2 O 7 2-^ ( aq ) + 6 Cl–( aq ) → 2 Cr 3+( aq ) + 3 Cl2( aq ) + 7 H 2 O( l ) (A) Increasing by 0.12 mol L -1^ min - (B) Increasing by 1.11 mol L -1^ min - (C) Decreasing by 0.12 mol L -1^ min - (D) Decreasing by 1.11 mol L -1^ min - 26. The isotope cobalt-57 has a half-life of 272 d. How long will it take a sample of 57 Co to decay to 38% of its original activity? (A) 103 d (B) 337 d (C) 188 d (D) 380 d 27. Which statement best describes the variation of the rate constant of a reaction with temperature? (A) The rate constant does not change with temperature because it is an unvarying characteristic of the specific reaction. (B) The rate constant typically decreases with increasing temperature because fewer molecules are able to adopt the required orientation at higher temperature. (C) The rate constant typically increases with increasing temperature because increasing the temperature increases the fraction of collisions that result in reaction. (D) The rate constant typically increases with increasing temperature because most reactions become more favorable as the temperature increases. 28. A mechanism for the reaction of nitric oxide with hydrogen to form water and nitrogen gas is proposed below. What rate law is predicted by this mechanism?
2 NO( g ) ⇄ N (^) 2O (^) 2( g ) fast, unfavorable equilibrium N (^) 2O (^) 2( g ) + H (^) 2( g ) → N (^) 2O( g ) + H (^) 2O( g )
slow, irreversible
N (^) 2O( g ) + H (^) 2( g ) → H 2O( g ) + N 2( g )
fast, irreversible
(A) Rate = k [NO] 2 (B) Rate = k [NO] 2 [H (^) 2] (C) Rate = k [NO] 2 [H 2] 2 (D) Rate = k
[NO]^2 [H 2 ]^2
[N 2 O][H 2 O]
Property of ACS USNCO – Not for use as USNCO Local Section Exam after March 31, 2022 Page 7
38. Which element is being reduced in the following equation? 3 Cu( s ) + 8 HNO3( aq ) → 2 NO( g ) + 3 Cu(NO 3 ) (^) 2( aq ) + 4 H 2 O( l ) (A) Cu (B) H (C) N (D) O
39. A galvanic cell is constructed under standard conditions using cobalt in cobalt(II) nitrate solution and indium in indium(III) nitrate solution. Which statements about this cell are correct?
Half-reaction E °, V Co 2+( aq ) + 2 e –^ → Co( s ) –0. In 3+( aq ) + 3 e –^ → In( s ) –0.
I. The standard cell potential is 0.46 V. II. Indium is the anode. (A) I only (B) II only (C) Both I and II (D) Neither I nor II
40. Molten sodium chloride is electrolyzed for 10. 0 minutes with a constant current of 10.0 A. What mass of sodium metal is produced? (A) 1.43 g (B) 2.20 g (C) 3.63 g (D) 4.41 g 41. The standard cell potential of a galvanic cell based on the reaction below is 1.10 V. Which concentrations would result in the largest measured voltage? Cu 2+(aq) + Zn(s) → Zn 2+(aq) + Cu(s) (A) [Cu 2+] = 1.0 M and [Zn 2+] = 1.0 M (B) [Cu 2+] = 3.0 M and [Zn 2+] = 1.0 M (C) [Cu 2+] = 1.0 M and [Zn 2+] = 3.0 M (D) [Cu 2+] = 3.0 M and [Zn 2+] = 3.0 M 42. The standard reduction potential of oxygen under acidic conditions at 298 K is +1.23 V. What is the standard reduction potential for the four-electron reduction of O 2( g ) under basic conditions? (A) 1.23 V (B) 1.02 V (C) 0.83 V (D) 0.40 V 43. Photons of what wavelength of light have an energy of 1.00 × 103 kJ mol-1^? (A) (^) 2.00 × 10 31 m (B) (^) 1.20 × 10 -7^ m (C) (^) 1.20 × 10 -4^ m (D) (^) 8.36 × 10 6 m 44. In which set are all three species isoelectronic? (A) H+, Li+, Na +^ (B) C, N – , O 2– (C) Se 2-^ , Br – , Rb +^ (D) I, Xe, Cs 45. Which change in principal quantum number n involves the greatest change in energy? (A) (^) n = 1 → n = 2 in H (B) (^) n = 2 → n = 3 in He+
(C) n = 3 → n = 4 in Li2+^ (D) n = 4 → n = 5 in Be 3+
46. Which gas-phase ion has the greatest number of unpaired electrons in its ground state? (A) Fe3+^ (B) Co 3+^ (C) Ni3+^ (D) Cu 3+ 47. Which principle restricts the occupancy of an atomic orbital to no more than two electrons? (A) The principle of conservation of energy (B) The principle of conservation of angular momentum (C) The Pauli exclusion principle (D) The Heisenberg uncertainty principle 48. When copper-64 decays by positron emission, what daughter nuclide is formed? (A)^64 Ni (B)^65 Ni (C)^64 Zn (D)^65 Zn 49. Which molecule has a nonzero dipole moment? (A) CF 4 (B) C 2 F 4 (C) SF 4 (D) SF 6 50. How many π bonds are in cyanogen, NCCN? (A) 2 (B) 4 (C) 6 (D) 7 51. In azomethane, H3CNNCH 3 , what are the molecular geometries around the carbon and nitrogen atoms, respectively? (A) Tetrahedral at carbon, bent at nitrogen (B) Tetrahedral at carbon, linear at nitrogen (C) Square planar at carbon, bent at nitrogen (D) Square planar at carbon, linear at nitrogen 52. What is the bond order of O 2 +? (A) 1.0 (B) 1.5 (C) 2.0 (D) 2.
Page 8 Property of ACS USNCO – Not for use as USNCO Local Section Exam after March 31, 2022
53. Which is the best explanation for phosphorus favoring formation of P 4 over P 2 molecules, while nitrogen forms only N 2 molecules? (A) Phosphorus-phosphorus π bonds are weaker than nitrogen-nitrogen π bonds. (B) Phosphorus can have an expanded octet while nitrogen cannot. (C) The nonbonding electrons on phosphorus occupy an unhybridized s orbital while the nonbonding electrons on nitrogen occupy hybrid orbitals. (D) The larger size of phosphorus allows the bonding electrons to be closer together.
54. In the octahedral complex Co(NH2CH 2 CO (^) 2) 3 , each glycinate ion NH (^) 2CH 2 CO 2 –^ binds to cobalt through its nitrogen atom and one of its oxygen atoms. How many stereoisomers of Co(NH (^) 2CH 2 CO (^) 2) 3 are possible? (A) 2 (B) 4 (C) 6 (D) 8 55. A molecule has the formula C5H (^) 10O. Which functional groups might it contain? I. Alcohol II. Ketone (A) I only (B) II only (C) Either I or II (D) Neither I nor II 56. How many distinct branched alkanes are there with the formula C 6 H 14? (A) 1 (B) 2 (C) 3 (D) 4 57. Which cycloalkane in its most stable conformation has average internal C–C–C bond angles most different from the value given? (A) Cyclopropane, 60° (B) Cyclobutane, 90° (C) Cyclopentane, 108° (D) Cyclohexane, 120° 58. Which gas is most reactive toward 1-hexene? (A) N 2 (B) O 3 (C) N 2 O (D) NH 3 59. Which structure depicts the enantiomer of the diol shown?
(A)
(B)
(C)
(D) The diol shown is achiral and does not have an enantiomer.
60. Which biomolecule does NOT contain C=O double bonds? (A) Sucrose (a carbohydrate) (B) Glyceryl trioleate (a lipid) (C) Phenylalanine tRNA (a nucleic acid) (D) Trypsin (a protein)
END OF TEST
