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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) 3/7 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. 4/7 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 6/7 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