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Exam 2013, questions
Chemistry 2 (CHEM10004)
University of Melbourne
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THE UNIVERSITY OF MELBOURNE SCHOOL OF CHEMISTRY SEMESTER 2 EXAMINATION, 2013 SUBJECT: CHEMISTRY 2, CHEM10004 Student Number: ___________________________ Exam Duration: 3 hours Reading Time: 15 minutes This paper has 19 pages. Authorized materials: Unassembled molecular model kits. Electronic calculators, including graphing 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 selected 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 © 2013, The University of Melbourne Page 1 of 19 CHEM10004 Semester 2, 2013 SECTION A The suggested time for this section is 1 hours Your answers to this section of the examination must be circled on this examination script, which must be handed in at the end of the examination period. You must also show your answers to this section, together with your student number, on the computer scan sheet provided. Please enter your student enrolment number in the spaces provided. In addition, ensure that your student enrolment number is recorded on each page of Section A. A table of selected physical constants, useful quantities and conversion factors is provided at the end of the exam paper in Appendix 1. Question A1. Which of the following is a nucleophile? A. H+ B. BF3 C. CrO3 D. FeCl3 E. None of the above (2 minutes) Question A2. Which of the following is the strongest acid? A. CH2FCO2H B. CHF2CO2H C. CF3CO2H D. CH3CO2H E. CH3OCH3 (2 minutes) © 2013, The University of Melbourne Page 2 of 19 CHEM10004 Semester 2, 2013 Question A5. The type of reaction depicted in Mechanism B in the scheme depicted above is: A. A nucleophilic addition/elimination reaction. B. An SN1 reaction. C. An SN2 reaction. D. An E2 reaction. E. None of the above. (2 minutes) Question A6. In Mechanism D depicted in the scheme above, tert-butoxide is acting as: A. An acid B. A base C. A nucleophile D. An electrophile E. None of the above (2 minutes) Question A7. Which of the mechanisms in the scheme depicted above leads to the product you expect following Zaitzev’s rule? A. Mechanism A. B. Mechanism B. C. Mechanism C. D. Mechanism D. E. None of the above. (2 minutes) © 2013, The University of Melbourne Page 4 of 19 CHEM10004 Semester 2, 2013 Student enrolment number.................................... Question A8. Which of the following methods leads to the formation of 4-nitrobenzoic acid as the major product? A. B. C. D. E. None of the above (5 minutes) Question A9. Which of the following general statements is INCORRECT? A. Sodium hydride is a poor reagent for reducing ketones. B. Grignard reactions involving carboxylic acids generally liberate molecular hydrogen (H2). C. The acidity of a carbon-hydrogen bond is affected by the hybridization of the carbon atom involved, with sp3 hybridized carbons providing the least acidic compounds. D. Markovnikov’s rule can be used to determine the major product from an electrophilic addition reaction. E. Tertiary (3°) alkyl halides usually do not undergo substitution reactions by an SN2 mechanism. (3 minutes) © 2013, The University of Melbourne Page 5 of 19 CHEM10004 Semester 2, 2013 Student enrolment number.................................... Question A12. Which of the following statements concerning the relative energies of wavefunctions is CORRECT? A. All the energy levels for the hydrogen atom are degenerate. B. The energy separation of the wavefunctions of the hydrogen atom increase as their energy increases. C. The energy separation of the wavefunctions of the hydrogen atom is constant. D. The energy separation of the wavefunctions of the hydrogen atom decrease as their energy increases. E. The energy separation of the wavefunctions for a particle in a 1D box model become more closely spaced as their energy increases. (2 minutes) Question A13. Which of the following statements concerning orbitals is INCORRECT? A. The size of a given orbital is dependent on the principal (n) quantum number. B. The shape of a given orbital is influenced by the angular momentum (l) quantum number. C. The shape of a given orbital may be influenced by the magnetic (ml) quantum number. D. The shape of a given orbital is influenced by the spin (ms) quantum number. E. The size of a given orbital should be thought of as extending to infinite distance from the nucleus. (3 minutes) Question A14. Which one of the following representations of the occupancy of a set of d-orbitals violates the Pauli exclusion principle? A. [⇅][￪][￪][ ][ ] B. [￪][￪][￪￪][ ][ ] C. [⇅][⇅][⇅][ ][ ] D. [⇅][￪][ ][￪][￪] E. [￪][￪][￪][￬][⇅] (2 minutes) © 2013, The University of Melbourne Page 7 of 19 CHEM10004 Semester 2, 2013 Question A15. Which of the following set of quantum numbers does NOT represent a valid solution of the Schrödinger equation? n l ml ms A. 2 1 0 +½ B. 1 1 0 +½ C. 2 0 0 -½ D. 6 3 1 +½ E. 4 3 2 -½ (3 minutes) Question A16. 2N2O5(g) → 4NO2(g) + O2(g) For the reaction, the rate of the reaction with respect to the reactant and the products is: A. B. C. D. E. = = = = = = = = None of the above. (3 minutes) © 2013, The University of Melbourne Page 8 of 19 CHEM10004 Semester 2, 2013 Question A20. Which statement about Collision Theory is CORRECT? A. Rate constants are typically larger the higher the temperature because a higher temperature allows the molecules to collide with the correct orientation. B. The collisional cross section depends on molecular orientation. C. An increase in the rate of diffusion increases the collisional frequency between molecules. D. The rate of reaction is independent of the concentration of reactants. (3 minutes) Question A21. The intracellular potassium ion concentration in a human neuron is 0 M. The extracellular potassium ion concentration is 0 M. Calculate the membrane potential (∆EM+) of the neuron at 37oC. A. -1 V B. -0 V C. 0 V D. 0 V E. 1 V (3 minutes) Question A22. Consider the following galvanic cell: Zn | Zn2+ || MnO4- | Mn2+ Use the standard reduction potentials (Appendix 2) to determine the cell potential when it is operated at pH = 2 with [MnO4-] = 0 M, [Mn2+] = 0 M and [Zn2+] = 0 M at 25oC. A. 2 V B. 2 V C. 2 V D. 2 V E. 2 V (3 minutes) Question A23. The magnetic moment of [V(en)3]Cl2 is 3 BM. How many unpaired electrons are present in the complex? A. 0 B. 1 C. 2 D. 3 E. 4 (3 minutes) © 2013, The University of Melbourne Page 10 of 19 CHEM10004 Semester 2, 2013 Student enrolment number.................................... Question A24. What is the oxidation state of the metal ion in [CrCl2(H2O)4]Cl and how many stereoisomers are possible? A. oxidation state = +1; possible isomers = 2 B. oxidation state = +2; possible isomers = 3 C. oxidation state = +2; possible isomers = 2 D. oxidation state = +3; possible isomers = 2 E. oxidation state = +3; possible isomers = 3 (3 minutes) Question A25. Calculate the spin only magnetic moment for high spin K3[Mn(ox)3]. A. 5 B. 2 C. 4 D. 3 E. 1 (3 minutes) Question A26. The hydrogen fuel cell is based on the reaction of hydrogen and oxygen to form water. Which of the following sets of statements are TRUE: A. This is an example of a secondary cell. The anode reaction involves oxidation of O2. The cathode reaction involves reduction of H2. B. Neither H2 nor O2 is oxidised or reduced. The cell’s energy comes from harnessing the steam produced from the exothermic reaction. C. A fuel cell is a galvanic cell in which the reactants are continuously supplied. The anode reaction involves oxidation of O2. The cathode reaction involves reduction of H2. D. A fuel cell is a galvanic cell in which the reactants are continuously supplied. The anode reaction involves oxidation of H2. The cathode reaction involves reduction of O2. E. Neither H2 nor O2 is reduced or oxidised. This is because fuel cells are different to normal galvanic cells. (3 minutes) © 2013, The University of Melbourne Page 11 of 19 CHEM10004 Semester 2, 2013 Student enrolment number.................................... Question A31. What volume, in mL, of 11 M HCl is required to make up a 300 mL solution of 2 M HCl? A. 31 mL B. 41 mL C. 63 mL D. 72 mL (2 minutes) Question A32. Determine the pH of a buffer solution that contains 0 M NH3 and 0 M NH4Cl. (Kb (NH3) = 1 × 10-5) A. 12 B. 9 C. 4 D. 4 E. 0 (2 minutes) Question A33. Determine the corresponding frequency for a wavelength of 736 nm. A. 1 × 10-3 Hz B. 221 Hz C. 2 × 105 Hz D. 4 × 1014 Hz (2 minutes) END OF SECTION A © 2013, The University of Melbourne Page 13 of 19 CHEM10004 Semester 2, 2013 Chemistry 2 Semester 2 Examination SECTION B The suggested time for this section is 1 hour ANSWER THIS SECTION IN THE EXAMINATION SCRIPT BOOKLET PROVIDED A table of selected physical constants, useful quantities and conversion factors is provided in Appendix 1. ANSWER THIS SECTION IN THE EXAMINATION SCRIPT BOOKLET PROVIDED Students are advised to answer ALL Questions, B1 to B9: Question B1. Consider the molecules A – D and answer the following questions: (a) Will isomer A or B react more rapidly in an SN2 reaction? Briefly explain your answer. (b) Will isomer A or B react more rapidly in an SN1 reaction? Briefly explain your answer. (c) Show all steps and reagents needed to convert C to D. (Hint: do not invent new chemistry). (10 minutes) © 2013, The University of Melbourne Page 14 of 19 CHEM10004 Semester 2, 2013 Question B3. Bitolterol is a β2-adrenergic receptor agonist used for the relief of bronchospasm in conditions such as asthma. (a) Complete this synthesis by drawing the structures of the products (C and D) in the scheme below. Hint: take advantage of the molecular formulas given. (b) Classify what class of reaction that Reaction 1 belongs to. (c) Classify what class of reaction that Reactions 2a and 2b belong to. (d) Classify what class of reaction that Reaction 3 belongs to. (e) Suggest an alternative reagent to H2/Pd-C for Reaction 3. (10 minutes) © 2013, The University of Melbourne Page 16 of 19 CHEM10004 Semester 2, 2013 Question B4. (a) Outline briefly the main reasons why the solutions to the Schrödinger equation for the “particle in a one-dimensional box” model differ substantially from those for the hydrogen atom. (b) Discuss briefly how the “particle in a one-dimensional box” model can be used to interpret the absorption or emission of light by a real chemical system. Provide an example of such a real chemical system. (4+3 = 7 minutes) Question B5. Using appropriately labelled schematic diagrams, where appropriate, show the steps that lead from a solution to Schrödinger’s wave equation to our three dimensional impression of a 1s atomic orbital for the hydrogen atom. (8 minutes) Question B6. Radical chain reactions involve a sequence of reactions in which a radical reacts and then is regenerated in subsequent reactions. The reaction of H2 and Br2 is a good example of a radical chain reaction. A reaction mechanism for this reaction is: 1: → 2 2: + → + Step 3: + → + Step 4: + → (a) What is the overall reaction described by the mechanism? (b) Identify the initiation, propagation and termination steps of the mechanism. (c) The experimentally determined rate equation for the production of HBr is: = = !"#$ %/ For the mechanism given above the rate of step 1= rate of step 4, and rate of step 2 = rate of step 3. Use the mechanism above to determine the expected rate law for the production of HBr. (4 + 4 + 7 = 15 minutes) © 2013, The University of Melbourne Page 17 of 19 CHEM10004 Semester 2, 2013 APPENDIX 1. Selected physical constants, useful quantities and conversion factors. Avogadro constant (NA) 6 × 1023 mol-1 1 Atomic mass unit (u) 1 × 10-27 kg Gas constant (R) 8 J K-1 mol-1 or 0 L atm K-1 mol-1 Speed of light (c) 2 × 108 m s-1 Planck constant (h) 6 × 10-34 J s photon-1 Rydberg constant (ℜ ) 3 × 1015 Hz Mass of an electron (me) 9 × 10-31 kg Bohr radius (ao) 53 pm 1 Atmosphere (atm) 101 325 Pa = 760 mm Hg Faraday constant (F) 9 × 104 C mol-1 RT/F (at 298 K) 0 V 2 RT/F (at 298 K) 0 V Absolute zero, 0 K -273 °C Specific heat of water 4 J g-1 ºC-1 APPENDIX 2: SELECTED STANDARD REDUCTION POTENTIALS Half Reaction - E° / V - Half Reaction 2+ - F2 + 2e → 2F IO4 + 2H+ + 2e- → IO3- + H2O MnO4-+8H++5e- → Mn2++ 4H2O 2 1 1 Cu + e → Cu 2H+ + 2e- → H2 Fe3+ + 3e- → Fe Cl2 + 2e- → 2ClO2 + 4H+ + 4e- → 2H2O MnO2+4H++2e- → Mn2++ 2H2O 1 1 1 Pb2+ + 2e- → Pb Sn2+ + 2e- → Sn Ni2+ + 2e- → Ni - Br2 + 2eAg+ + eFe3+ + eI2 + 2eCu+ + e- → 2Br→ Ag → Fe2+ → 2I→ Cu 1 0 0 0 0 Fe2+ + 2eCr3+ + eCr3+ + 3eZn2+ + 2e[Zn(NH3)4]2+ + 2e- E° / V + → Fe → Cr2+ → Cr → Zn → Zn + 4 NH3 0 0 -0 -0 -0 -0 -0 -0 -0 -0 -1 Cu2+ + 2e- → Cu Hg2Cl2 + 2e- → 2Hg + 2Cl- 0 0 Mn2+ + 2e- → Mn Al3+ + 3e- → Al -1 -1 AgCl + e- → Ag + Cl- 0 Na+ + e- → Na -2 © 2013, The University of Melbourne Page 19 of 19
Exam 2013, questions
Course: Chemistry 2 (CHEM10004)
University: University of Melbourne
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