Download First Round SwissChO 2015

First Round SwissChO 2015
Information
• This exam should be solved within approximately one hour, using only books and a calculator. The answers should be copied to the separate answer sheet using a dark felt tip
pen or ballpoint pen. You may not use a pencil, as the machine-assisted evaluation is not
capable of registering that.
• It is possible that more than one answer is correct.
• Everybody who was born on July 1st 1995 or later and still is not enrolled at a university
is eligible to participate.
• You can also enter the answers on our homepage http://www.swisscho.ch.
SwissChO 2015
Multiple Choice Exam
1. Copper is an element that naturally occurs as a mixture of two isotopes, 63Cu and 65Cu
with the masses 62.98773 u and 64.92825 u, respectively. The mass of the mixture is
63.546 u.
What are the mass percentages w63 and w65 of the two isotopes?
A.
B.
C.
D.
E.
w63 = 57.93 %
w63 = 28.77 %
w63 = 71.23 %
w63 = 69.15 %
w63 = 30.85 %
and
and
and
and
and
w65 = 42.07 %
w65 = 71.23 %
w65 = 28.77 %
w65 = 30.85 %
w65 = 69.15 %
2. Order the following hydrogen halides according to their relative acidic strength:
A.
B.
C.
D.
E.
HF < HCl < HBr < HI
HF > HCl > HBr > HI
HCl > HBr > HF > HI
HCl < HBr < HF < HI
HI < HBr < HF < HCl
3. The solubility constant for lead(II) iodate Pb(IO3 )2 is Ksp = 3.69 · 10−13 M3 . What is the
concentration of the iodate anion in a saturated solution of lead(II) iodate?
A.
B.
C.
D.
E.
1.435 · 10−4
1.356 · 10−4
9.037 · 10−5
7.173 · 10−5
4.518 · 10−5
M
M
M
M
M
4. What is the phase transition from gas to liquid called?
A.
B.
C.
D.
E.
Recombination
Vaporisation
Deposition
Resublimation
Condensation
5. Consider the complete combustion of pentanone:
a C5 H10 O + b O2 −−→ c CO2 + d H2 O
Which combination a; b; c; d of the stoichiometric coefficients is correct?
A.
B.
C.
D.
E.
1; 6; 4; 4
1; 6; 5; 5
1; 7; 5; 4
1; 7; 5; 5
2; 13; 10; 10
2/7
SwissChO 2015
Multiple Choice Exam
6. Consider the reaction of sodium perchlorate NaClO4 to sodium chlorate NaClO3 at room
temperature (20 ◦ C), under the release of oxygen:
2 NaClO4 −−→ 2 NaClO3 + O2 (g)
The following data is given:
Substance
NaClO4
NaClO3
O2 (g)
∆f H ◦
kJ mol−1
-383.3
-365.8
0.0
S◦
J mol−1 K−1
142.3
123.4
205.0
Based on the data above, which of the following statements are true?
A.
B.
C.
D.
E.
The reaction is spontaneous.
The reaction is exergonic.
The reaction is endergonic.
The reaction is endothermic.
The reaction increases entropy.
7. Dimethyl sulfoxide (CH3 )2 SO is a polar solvent. According to VSEPR theory, which geometry does it adopt?
A.
B.
C.
D.
E.
Bent
Trigonal pyramidal
Tetrahedral
Trigonal bipyramidal
Octahedral
8. Photons are emitted from a laser at λ = 492 nm. What is the energy of one mol of these
photons?
A.
B.
C.
D.
E.
4.026 · 10−19 J
2.712 · 10−12 J
5.870 · 10−8 J
2.425 · 105 J
6.687 · 1025 J
9. What is the molecular mass of 2-(Trimethylsilyl)propanal?
A. 22 g mol−1
B. 65 g mol−1
C. 72 g mol−1
D. 130 g mol−1 E. 144 g mol−1
10. What is the maximal amount of aluminium extractable from 94.4 g aluminium(III) oxide
Al2 O3 ?
A. 25.0 g
B. 37.7 g
C. 50.0 g
11. What is the name of Na2 [PdCl6 ]?
A.
B.
C.
D.
E.
Sodium hexachloropalladate(IV)
Bis-sodium platinohexachloride(IV)
Sodium hexachloropadate(III)
Palladiohexachloridum(IV) disodii
Bis-sodium palladohexachloride(IV)
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D. 94.4 g
E. 189 g
SwissChO 2015
Multiple Choice Exam
12. What are the oxidation numbers of oxygen and sulfur in SO3− ?
A.
B.
C.
D.
E.
S: -I
S: 0
S: II
S: IV
S: V
O: -I
O: -III
O: -II
O: -I
O: -II
13. Mark all possible products of the reaction of water and carbon monoxide.
A. H2
B. O2
C. CO2
D. C2 H2
E. CH3 OH
14. You dissolve 31 g of Na2 O in 250 mL of distilled water. Mark the correct statements.
A.
B.
C.
D.
E.
c(Na+ ) = 2 mol L−1
c(Na+ ) = 4 mol L−1
c(O2− ) = 1 mol L−1
c(OH− ) = 2 mol L−1
c(OH− ) = 4 mol L−1
15. What is the pH of a 0.1585 mM solution of HCl?
A. 0.5
B. 0.8
C. 3.5
D. 3.8
E. 4.2
16. You performed absorbance measurements at a fixed wavelength on a substance in an aqueous solution at the concentrations 0.01 M and 0.05 M in a cuvette with length 1 cm. The
absorbances measured were 0.25 and 1.25, respectively. What is the molar extinction
coefficient of the substance?
Hint: The law of Lambert-Beer is A = "cl.
A.
B.
C.
D.
E.
0.04 L mol−1 cm−1
0.04 mol L−1
25 L mol−1 cm−1
25 mol L−1
None of the above.
17. A local factory called to have you assess the safety of their process. They want to perform
a reaction that releases heat at a rate of 27.8 MJ h−1 and the mixture (total mass 550 kg)
has a heat capacity of cs = 1.42 kJ kg−1 K−1 . A cooling system is in place, it operates at
22.4 MJ h−1 . Under the assumption of optimal stirring, and starting at room temperature
(293 K); how long does it take the reaction to reach 150 ◦ C?
A. 9.93 h
B. 18.8 h
C. 21.7 h
18. A catalyst . . .
A.
B.
C.
D.
E.
...
...
...
...
...
changes the reaction pathway.
lowers the free energy difference ∆G.
is always made of a noble metal.
lowers the activation energy.
is none of the above answers.
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D. 37.6 h
E. 188 h
SwissChO 2015
Multiple Choice Exam
19. What type of molecular orbital is depicted in the following figure?
A.
B.
C.
D.
E.
s
p
sp2
σ
π
20. L-Alanine is a simple α-amino acid, bearing only a methyl group on the side chain. What
is its systematic IUPAC-Name?
H 2N
COOH
A.
B.
C.
D.
E.
(R)-1-Amino-1-methylpropanoic acid
(S)-1-Amino-1-methylpropanoic acid
(R)-2-Aminopropanoic acid
(S)-2-Aminopropanoic acid
(R)-2-Propanoic amino acid
21. 2-Methyl-2-iodopropane is relatively unstable and decomposes easily at temperatures over
60 ◦ C. What kind of decomposition product would you expect? Hint: The decomposition
is facilitated by the addition of a base.
B.
A.
C.
D.
E.
22. What is the most likely product of the following reaction?
AlCl3
O
Cl
O
O
O
O
O
A.
B.
C.
5/7
D.
E.
SwissChO 2015
Multiple Choice Exam
23. How many constitutional isomers with the formula C5 H10 are there?
A. 3
B. 7
C. 10
D. 13
E. 17
24. What is the product of the reaction of 1-propene with HBr?
Br
Br
A.
B.
Br
Br
C.
D.
E.
D. E1
E. E2
Br
25. Name the following reaction.
SH
H
H
A. SN 1
I
H
H
S
B. SN 2
C. SN i
HI
26. You have a substance that contains 40.00 % carbon. Which of the following formulae fits
that observation?
A. C2 H6 O
B. C3 H6 O
C. C3 H6 O3
D. C6 H12 O
E. C8 H16 O2
27. Let’s have a closer look at the Haber–Bosch process. The chemical equation for this process
is as follows:
−−
*
N2 + 3 H2 −
∆H ◦ = −92.0 kJ
)
− 2 NH3
Which measures can be taken to shift the equilibrium towards ammonia?
A.
B.
C.
D.
E.
Raising the temperature
Lowering the temperature
Increasing pressure
Decreasing pressure
Adding more hydrogen
28. Given the following electrode potentials:
Half Cell Reaction
Cs+
+ e–
→ Cs
3+
–
Y
+ 3e → Y
3+
Al
+ 3e– → Al
Zn2+ + 2e– → Zn
Cu2+ + 2e– → Cu
Ag+ + e–
→ Ag
+
–
Au
+ e
→ Au
E◦ / V
–3.03
–2.37
–1.66
–0.76
+0.34
+0.80
+1.83
Which of the following theoretical galvanic cells would deliver the highest voltage?
A.
B.
C.
D.
E.
Y | Y3+ || Al3+ | Al
Cs | Cs+ || Al3+ | Al
Y | Y3+ || Cu2+ | Cu
Zn | Zn2+ || Ag+ | Ag
Cu | Cu2+ || Au+ | Au
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SwissChO 2015
Multiple Choice Exam
29. Given are three hypothetical compounds A, B, and C that only have one reduced and one
oxidated form, indicated by the indexes ox and red respectively. Three experiments are performed to determine which substance is the noblest and which the most ignoble. Therefore
in each case two substances were mixed and it was reported if a reaction could be observed.
The results are in the following table:
Reaction Partners
Cox + Bred
Aox + Bred
Aox + Cred
Reaction Observed
YES
YES
NO
If you put the compounds in order from left, being the noblest, to right, being the most
ignoble, which would be the right arrangement?
A. A, B, C
B. B, C, A
C. C, A, B
D. A, C, B
E. C, B, A
Questions without any influence on the result
30. How did you know about the Swiss Chemistry Olympiad?
A.
B.
C.
D.
E.
Teacher
Colleagues
SwissChO presentation
Press
Others
31. Would you take part at the Central Exam in January next year in case you qualify?
A. Yes
B. No
7/7