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Exam November 2016, questions
Chemistry 2 (CHEM10004)
University of Melbourne
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THE UNIVERSITY OF MELBOURNE SCHOOL OF CHEMISTRY SEMESTER 2 EXAMINATION, 2016 SUBJECT: CHEMISTRY 2, CHEM10004 Student Number: ___________________________ Exam Duration: 3 hours Reading Time: 15 minutes This paper has 22 pages. Authorized materials: Unassembled molecular model kits. Non-programmable, non-graphical calculators. Note: Calculators are permitted in accordance with the rules of the Faculty of Science. They may be used for the processing of numerical information only. They must not have been programmed nor should they store additional information. Calculators will be randomly checked during the course of the examination. Instructions to Invigilators: Students will attempt Section A on the examination paper itself. For Section A, students must also enter their answers on the computer scan sheet provided. Please remind students to leave the exam paper and the scan sheet on their desk for collection at the end of the examination. A 14-page script book is required for Section B of the paper. Instructions to Students: This assessment consists of two sections, Section A and Section B. Section A carries one half of the total marks available while Section B carries the remaining half. It is suggested that you spend equal time on each section. The marks available for each question are proportional to the suggested completion times given at the end of each question. You must answer Section A on the paper itself and also enter your answers on the computer scan sheet provided. Answer Section B in the examination script book provided. A table of selected physical constants, useful quantities and conversion factors is given in Appendix 1 and a table of standard reduction potentials is given in Appendix 2. Please ensure that the exam paper, the scan sheet and the script book used to answer Section B are all left on your desk at the end of the examination. Paper to be held by Baillieu Library - YES © 2016, The University of Melbourne Page 1 of 22 CHEM10004 Semester 2, 2016 This page has been intentionally left blank. © 2016, The University of Melbourne Page 2 of 22 CHEM10004 Semester 2, 2016 Question A2. The type of reaction shown in step 1 of the scheme shown above is: A. an SN2 reaction B. an E1 reaction C. a nucleophilic addition reaction D. a nucleophilic addition/elimination reaction E. None of the above. (2 minutes) Question A3. The most appropriate reagent to effect the transformation depicted in step 2 of the sequence depicted above is: A. NO2 gas B. HNO3 C. HNO3/H2SO4 D. NO3 E. None of the above. (3 minutes) Question A4. The type of reaction shown in step 2 of the scheme shown above is: A. a nucleophilic aromatic substitution B. an electrophilic aromatic substitution C. a nucleophilic addition/elimination reaction D. an electrophilic elimination reaction E. None of the above. (2 minutes) © 2016, The University of Melbourne Page 4 of 22 CHEM10004 Semester 2, 2016 Student enrolment number.................................... Question A5. Benzyl acetate, CH3CO2CH2C6H5, gives the characteristic flowery aroma to jasmine. Which sequence of reagents provides a plausible series of steps for the synthesis of benzyl acetate from benzyl bromide (C6H5CH2Br): A C6H5CH2Br B C6H5CH2Br C C6H5CH2Br D C6H5CH2Br E C6H5CH2Br NaOH(aq) C2H5COCl NaOH(aq) CH3CH2OH, H+ NaOH(aq) CH3CH2Cl NaOH(aq) KMnO4 NaOH(aq) CH3COCl CH3CH2OH, H+ (3 minutes) Question A6. Which one of the compounds listed below would be expected to react the fastest in an SN2 reaction with sodium bromide? A. methanol B. 2-iodobutane C. 2-methyl-2-iodobutane D. sodium iodide E. None of the above would react with sodium bromide. (3 minutes) © 2016, The University of Melbourne Page 5 of 22 CHEM10004 Semester 2, 2016 Student enrolment number.................................... Question A9. Which one of the following is the most stable carbocation? B. A. D. C. E. (3 minutes) Question A10. When treated with sodium hydroxide, the alkyl chloride shown below gives five possible elimination products (1-5). NaOH Cl alkyl chloride + 1 + + 2 3 + 4 5 Which product(s) constitute the major species formed? A. 1 B. 2 and 3 C. 4 D. 4 and 5 E. 5 (3 minutes) Question A11. In a photoelectric effect experiment, what is the velocity of an electron emitted from a caesium (Cs) surface (Ebind = 206 kJ mol-1) by a photon with wavelength of 215 nm? A. 1 ´ 106 m s-1 B. 5 ´ 103 m s-1 C. 3 ´ 108 m s-1 D. 7 ´ 106 m s-1 E. 2 ´ 105 m s-1 (3 minutes) © 2016, The University of Melbourne Page 7 of 22 CHEM10004 Semester 2, 2016 Question A12. What is the De Broglie wavelength of an electron, photoemitted from a metal surface with a kinetic energy of 1 × 10-19 J? A. 7 ´ 10-10 m B. 1 ´ 10-10 m C. 0 ´ 10-10 m D. 1 ´ 10-9 m E. 7 ´ 10-9 m (3 minutes) Question A13. Which one of the following set of quantum numbers does NOT represent a valid solution of the Schrödinger equation for the hydrogen atom? n l ml ms A. 5 3 -2 -½ B. 3 0 0 -½ C. 3 3 -1 +½ D. 1 0 0 +½ E. 2 1 0 +½ (2 minutes) Question A14. Which one of the following set of quantum numbers is associated to a 3d atomic orbital? n l ml ms A. 5 2 0 -½ B. 3 0 0 -½ C. 3 2 2 +½ D. 3 1 -1 -½ E. 4 2 1 +½ (2 minutes) © 2016, The University of Melbourne Page 8 of 22 CHEM10004 Semester 2, 2016 Question A18. The hydrolysis of sucrose to glucose and fructose is described by the reaction below: C12H22O11 + H2O ® C6H12O6 + C6H12O11 The activation energy for this reaction is 108 kJ mol-1. If at 35 oC, k for this reaction is 6 × 10-5 s-1, what is the rate constant, k, at 45 oC closest to? A. 9 x 10-5 s-1 B. 0 x 10-4 s-1 C. 1 x 10-4 s-1 D. 2 x 10-4 s-1 E. 3 x 10-4 s-1 (3 minutes) Question A19. The reduction of NO to N2 by hydrogen is proposed to have a mechanism involving the following elementary steps: 2NO ® N2O2 N2O2 + H2 ® N2O + H2O N2O + H2 ® N2 + H2O In the overall stoichiometric reaction, at any time t, A. d[NO]/dt = d[H2O]/dt = 2d[N2]/dt B. d[N2O]/dt = d[N2]/dt = −d[H2]/dt C. d[H2O]/dt = d[N2]/dt = d[N2O2]/dt D. d[NO]/dt = d[N2]/dt = d[N2O]/dt E. d[NO]/dt = −2d[N2]/dt = d[H2]/dt (3 minutes) © 2016, The University of Melbourne Page 10 of 22 CHEM10004 Semester 2, 2016 Student enrolment number.................................... Question A20. The formation of gaseous HBr from hydrogen and bromine is proposed to occur via the mechanism, which is given below: Which one of the following statements is TRUE? A. The steps leading to HBr as product, are chain termination steps. B. Bromine molecules are chain carriers. C. Bromine atoms are chain carriers, but hydrogen molecules are not. D. Hydrogen atoms are chain carriers and so are bromine atoms. E. There are two chain termination steps in the scheme shown here. (3 minutes) Question A21. The following concentration/time data were determined at 120 oC for the breakdown of benzoyl peroxide, a radical initiator in some free radical polymerisation chain reactions. Time (min) [Benzoyl peroxide] × 102 (M) 0 15 30 45 60 75 2 1 1 0 0 0 The rate constant for this reaction is: A. 1 min-1 B. 0 min-1 C. 5 x 10-4 s-1 D. 3 x 10-4 s-1 E. Cannot be determined from this data. (3 minutes) © 2016, The University of Melbourne Page 11 of 22 CHEM10004 Semester 2, 2016 Student enrolment number.................................... Question A24. Which one of the following changes will lead to the LARGEST increase in Ecell? A. Lowering the concentration of Ag+ in the LEFT half cell and raising the concentration of SO42- in the RIGHT half cell. B. Lowering the concentration of Ag+ in the LEFT half cell and lowering the concentration of SO42- in the RIGHT half cell. C. Raising the concentration of Ag+ in the LEFT half cell and raising the concentration of SO42- in the RIGHT half cell. D. Raising the concentration of Ag+ in the LEFT half cell and lowering the concentration of SO42- in the RIGHT half cell. E. Doubling the size of the electrodes. (2 minutes) Question A25. By considering the standard reduction potentials given in Appendix 2, decide which of the following metals could be used as a sacrificial coating to protect nickel metal, Ni(s)? A. Cu B. Mg C. Ag D. Sn E. Any of these metals. (2 minutes) Question A26. Which one of the following only includes the transition metals in common oxidation states (i. oxidation states observed for the ions in aqueous solution in the presence of dioxygen)? A. VV, CrVI and MnIII B. VIV, CrII and TiII C. CrIII, MnII and FeIII D. TiIII, VII, and MnII E. FeIV, CoII and CuIII (3 minutes) © 2016, The University of Melbourne Page 13 of 22 CHEM10004 Semester 2, 2016 Question A27. Which one of the following cations would generate solutions with the HIGHEST acidity (i. lowest pKa)? A. Fe3+ B. Ca2+ C. Na+ D. Cu2+ E. All cations have the same pKa. (2 minutes) Question A28. Which one of the following statements is INCORRECT? A. Enterobactin is a good ligand for iron. B. The crystal field stabilisation energy for low spin octahedral Fe2+ is -2 + 2P. C. The compounds cis- and trans-[PtCl2(NH3)2] have identical anti-cancer properties. D. Porphyrin is a tetradentate ligand. E. Iron is typically in the +3 oxidation state at the surface of lakes/the ocean. (3 minutes) Question A29. Which one of the following statements is INCORRECT? A. Copper is important in a number of metalloenzymes. B. Cyanide is a stronger field ligand than bromide. C. The coordination complex [MnO4]− has a tetrahedral coordination geometry. D. Amino acids can be ligands for transition metals. E. Mn2+ complexes often have a magnetic moment, µ, of 6 BM. (3 minutes) Question A30. Which one of the following ions is most likely to undergo a Jahn-Teller tetragonal elongation? A. Cu+ B. Mn7+ C. Cr2+ © 2016, The University of Melbourne D. Ti4+ E. Zn2+ (2 minutes) Page 14 of 22 CHEM10004 Semester 2, 2016 Question A35. Determine the pH of a 0 M aniline (C6H5NH2). [Kb(aniline) = 3 × 10−10] A. 0 B. 8 C. 7 D. 5 E. 3 (2 minutes) Question A36. The wavelength of light having a frequency of 8 × 1014 Hz is closest to: A. 0 µm B. 1 µm C. 1215 nm D. 3640 nm E. 121 nm (2 minutes) END OF SECTION A © 2016, The University of Melbourne Page 16 of 22 CHEM10004 Semester 2, 2016 Chemistry 2 Semester 2 Examination SECTION B The suggested time for this section is 1 hour. Note that a table of selected physical constants, useful quantities and conversion factors is provided in Appendix 1, a table of standard reduction potentials is given in Appendix 2 and molar masses in Appendix 3. ANSWER THIS SECTION IN THE EXAMINATION SCRIPT BOOKLET PROVIDED Students are advised to answer ALL Questions, B1 to B9: Question B1. Consider the bromoalkane (A) depicted below (Ph = phenyl = C6H5). Br H Ph Ca H Cb H CH3 A (a) When treated with the hindered base potassium t-butoxide (KOC(CH3)3), compound A undergoes elimination. i. Draw all three different alkenes that are formed in this elimination reaction. ii. Which of these is the major product? (b) Two of these alkenes arise from anti-periplanar transition states of different conformations that can be represented by looking down the Ca–Cb bond of a Newman projection: H Ca Br i. Using the structure above, draw one of these Newman projections in your scriptbook. ii. Link this conformation to the appropriate alkene of your answer to part (a) (i) above. (question continued over page) © 2016, The University of Melbourne Page 17 of 22 CHEM10004 Semester 2, 2016 Question B3. Suggest a synthesis of m-bromobenzoic acid, C, starting from benzene, D. You will need to show all reagents used in this multi step synthesis as well as the product(s) of each step. Identify each class of reaction you use in your synthesis (e. electrophilic aromatic substitution, E2 etc.). CO2H Br C D (10 minutes) Question B4. In analysis of the spectra of atoms and ions the following expression is commonly used: æ1 1ö DE n = -2 x 10 Z çç 2 - 2 ÷÷ è n f ni ø -18 2 J (a) Define the terms DEn, Z, nf and ni in this equation. (b) Calculate the energy of the emitted photon which gives rise to the second Balmer line in the hydrogen atom emission spectrum. (c) What is the frequency (Hz) and wavelength (nm) of the emitted photon which gives rise to the second Balmer line in the hydrogen atom emission spectrum? (d) What minimum energy is required to remove the single remaining electron from a ground state Li2+ ion? (e) Would a photon of higher or lower wavelength be required to ionise the Li2+ ion if it were not in its ground state? Briefly explain your answer. (10 minutes) © 2016, The University of Melbourne Page 19 of 22
Exam November 2016, questions
Course: Chemistry 2 (CHEM10004)
University: University of Melbourne
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