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Unformatted text preview: Please Print Your Name (Family, First): , Student Number: UNIVERSITY OF TORONTO Faculty of Arts and Science APRIL/MAY EXAMINATIONS 2008 I CHMlSlYl Y Duration - 3 hours Examination aids: calculator, molecular model kit Instructions: Please print your name on every sheet. Please write solutions IN INK in the spaces provided. If there is insufficient space write on the back of the pages. The last 3 pages can be removed from the exam booklet. They contain supplementary information. PLEASE HAND IN ALL OF THE PAGES OF THE EXAM Organic chemistry “ms” _ Physical chemistry Initials for re-reading: Page 1 of21 Please Print Your Name (Family, First): , ORGANIC CHEMISTRY SECTION - / — — 5 5 /5 /15 Subtotal ORGANIC CHEMISTRY QUESTIONS 1. (5 Marks) Draw the mechanism for the following reaction using curved arrows to show electron movement. HvBr Br 2. (5 marks) Label the following ions or molecules as electrophilic or nucleophilic: (a) a carbocation (b) OH" (C) NHs (d) HCl (e) a proton Page 2 of21 Please Print Your Name (Family, First): 3. (5 marks) Part A: Draw the curved arrows and predict the products of the reaction: H G CH3O H Br ———> Part B: Draw the curved arrows to explain the products observed: 0e 0 G ____* /“\ + Cl Et NMe2 CI Page 3 onI Please Print Your Name (Family, First): INORGANIC SECTION / / / — _ __ _ _- __ — — - Subtotal /45 INORGANIC CHEMISTRY QUESTIONS 4. (5 marks) Draw a diagram using boxes to show the valence orbitals of a zinc atom. Label these boxes. Fill these boxes to produce the correct ground-state electron configuration of zinc (Zn). Write out the condensed electron configuration of zinc (e. g. Be = [He]252). 5 (5 marks) (a) Arrange these elements in order of increasing size: Cl, K, S < < (b) Which element would you expect to be more metallic: Mg or Ra? Page 4 of21 Please Print Your Name (Family, First): , 6. (5 marks) Are the bonds in the following substances ionic, non-polar covalent or polar covalent? KCI P4 BF3 $02 7. (5 marks) Draw the Lewis structure, suggest the hybridization of the central atom and name the shape of the following molecules: (3) PFs (b) BeHz 8. (5 marks) Water in its pure state can engage in as many as four hydrogen bonds. Explain by use of a diagram. Page 5 of21 Please Print Your Name (Family, First): 9. (5 marks) Tantalum (Ta, density =16.634 g/cm3 and M = 180.9479 g/mol) has a body centred cubic structure with a unit-cell edge length of 0.33058 nm. (a) Draw the unit cell showing the position of the Ta atoms as small circles. Describe the diagram in words. (b) Use the data for Ta provided above to calculate Avogadro’s number. Show all of the steps in this calculation. (Hint: first calculate the volume of a unit cell in ems, then the density of a unit cell by using the number of atoms in the unit cell and their weight in grams). 10. (5 marks) Describe differences in the structure and bonding of graphite compared to C60 Page 6 of21 Please Print Your Name (Family, First): _______3 11. (5 marks) A 0.035 M solution of a weak acid has a pH of 4.88. What is the Ka of the acid? 12. (5 marks) [F eF 6]3' is a high spin complex. Draw the orbital energy splitting diagram for its d orbitals and indicate how the electrons are placed in these orbitals. Energy Page 7 of21 Please Print Your Name (Family, First): , PHYSICAL CHEMISTRY SECTION Subtotal 13. (15 marks) a) Write down the definition of Gibbs free energy. Describe how this function relates to the second Law of Thermodynamics with respect to predicting whether a reaction will occur as written or not. b) Briefly define a catalyst. Draw a reaction energy diagram to illustrate the effect of a catalyst on reaction. Page 8 of 21 Please Print Your Name (Family, First): , c) Define a first order reaction and give an example. d) Define the transition state in a chemical reaction. e) List the different mechanisms by which one can speed up a chemical reaction towards the favoured product. Page 9 of21 Please Print Your Name (Family, First): , 14. (15 marks) a) Balance the skeleton reaction: Mn02(s) + Ag+(aq) 9 MnO4'(aq) + Ag(s) [basic] b) From the attached tables, calculate Eocen constructed fi'om the corresponding oxidation/reduction half reactions and state whether the reaction is spontaneous. c) Draw a schematic of the electrochemical cell using the above oxidation/reduction reactions for the half cells. Label the anode, cathode, salt bridge, direction of current flow, direction of ion motion in the salt bridge. (You can assume Mn02(s) is coated as a thin layer on an electrode.) Page 10 of21 1 Please Print Your Name (Family, First): 15 (15 marks) The following kinetic data has been obtained for the reaction: 2N02 9 2N0 + 02 5 U 6‘— M (.201) C en [ration (I 0"2 M) 0 100 200 300 Time (s) The data plotted as a first order reaction and second order reaction with respect to N02 concentration gives: Note that A on the scale of the figure below stands for N02. Nitrogen Dioxide Decomposition 400 0 0 0 '1 00 200 0 1 00 200 300 Time (3) Tune (s) a) What is the order of the reaction rate with respect to N02? Explain briefly. b) The first step in the overall mechanism is found to involve the process: 2N0; 9 NO; + NO. Propose a mechanism that is consistent with the above data. Page 11 of21 d Please Print Your Name (Family, First): 16. (15 marks) The electrolysis of water can be constructed from the following standard reduction half reactions: E0 02(g) + 4H+(aq) + 4e“ -> 2H20(1) +1.229 v 4H20(1) + 4e" -> 2H2(g) + 4OH' -0.828 v a) Write down the balanced equation and give the minimum applied voltage required for splitting water into hydrogen and oxygen gas under standard conditions. b) The observed voltage to obtain appreciable hydrolysis of water is higher than the calculated minimum voltage. Explain. Page 12 of21 0 Please Print Your Name (Family, First): , c) The above half reactions are for standard conditions in which one half cell has pH=0 and the other at pH=14. Calculate the minimum applied voltage for splitting water for neutral pH. Note, you have to use the half reactions with the reference hydrogen electrode and the Nernst equation to arrive at corrected reduction potentials relative to the standard hydrogen electrode for the different concentrations of If and OH' under nonstandard conditions (recall pH=7; [H] = [OH‘] = 10' ). Page 13 onI Please Print Your Name (Family, First): 17. The burning of hydrogen gas does not contribute to atmospheric C02 levels that have been identified as a major contributor to global warming. The cleanest fossil fuel to compare to a hydrogen fuel economy is propane. a) Taking the cell potential for the hydrolysis of liquid water (neutral pH) to be -1 .23V, calculate the free energy that can be extracted from hydrogen gas, i.e. for the reaction: 2H2(g) + 02(g) 9 2H20(g)- Given: H20(1) -) H20(g); AG0 = 8.6 kJ/mole (Hint: The cell potential of -1 .23V refers to hydrolysis of H20(1). You need to take into account the change from liquid to gas phase.) Page 14 of21 ~.J Please Print Your Name (Family, First): (Question 17, continued) b) Using AGO? (C3Hg(g)) = -245 kJ/mole, AG°f (C02(g)) = —394 kJ/mole, and AG°f (H20(g)) = -229 kJ/mole, calculate the maximum work that can be extracted from the combustion of 700 g of C§fl§(g)_(approximately 1 liter of liquid propane) with oxygen under standard conditions. (Notes: atomic mass of C = 12.01 g, atomic mass of H = 1.008 g) Page 15 of21 J Please Print Your Name (Family, First): (Question 17, continued) c) From a), one can calculate that it takes 144 moles of H13); to deliver the same amount of maximum work as 700 g of propane. How long would it take to produce 144 moles of hydro gen gas by electrolysis of water (question 16) with a current of 1000 Amps at 5 Volts? (Note at the present cost of electricity, the cost for this much power consumption to generate hydrogen gas is more than 100x that of propane or other fossil filels.) Page 16 of21 \J Please Print Your Name (Family, First): 18. (15 marks) The primary process of vision involves a photoinduced cis to trans isomerization around the C11-C12 bond of retinal, the photoactive molecule inside the protein complex rhodopsin (see below). This leads to the change in position of a hydrogen atom that ultimately undergoes proton transfer across this membrane-bound protein (rhodopsin) to stimulate the optic nerve. 11 11 \ 12 light /\ —’ 12 H Lys "I1 11-cis-rhod0psin \@ H all-trans bathorodopsin N / Lys E Photoisomerization of retinal in rhodopsin a) Draw an ener dia am for this reaction coordinate for the dark case (no light) in which the cis form is more stable than the trans form of retinal. The ground state reaction is endothermic by 32 kJ/mole and the activation barrier is 95 kJ/mole. Include in your drawing the position of the transition state. Schematically depict specific motions at the Cl 1-C12 position in forming the transition state upon illumination with light (you can use 2-butene as a model to show the key motions involved). Page 17 of21 Please Print Your Name (Family, First): b) Assuming an Arrhenius prefactor of 1x1012 sec", calculate the rate constant at 37 SQ (body temperature) for the back reaction in which the trans is converted back to the light active cis form to regenerate the eye response after light absorption. (You must use the activation barrier for the back reaction.) Compare the lifetime of the trans isomer to the requirement for the appearance of live motion using 25 frames per second in video recording. c) What is the effect of increased body temperature on the equilibrium constant for the interconversion between cis and trans retinal, i.e. do you have more or less photoactive cis retinal present at higher temperatures? Briefly discuss in terms of the affect of temperature on the forward and backward rates for this system. Page 18 of21 4 Please Print Your Name (Family, First): , Table of electrochemical potentials I .................................................................................. .: .......................... .;...:,.:..;._.‘_;4-.::;..;;._,; ____ -;._._.._' A " l Standar Potential :iHalf-Reaction 903:8.) H266): 7: , .............. ..._......i......~...,WW___~..._...... $11009an992% V - iimaqw e' aMnZYaq) .. . éMn04‘<aq>+ 8Hf<aq> + 5e'—+Mn2*<aq>+4Hzo<1). . .. .. iC103'(aq)+ mm) + 56 ,—> l/zclzcaq) + , c12<g> +2e.i,—> 293%» l .k we a. 'gAgJ’ + e' —> Ag(§) H §Mn04'(aq) + 2H20(1) + 3e' —-> Mn02(s + 4OH'(a §c103'<aq)+ H200) +_2ei—>C_1027<aq>.+ ., .. W §Cu2+(aq) + 2e' —> Cu(s) +...2..é: > lFe3+(aq) + 3e" —) Fe(s) ’ ,. l l J 'lCd2+('<‘Q).+ 26' " (31(3). 3§Fe2+(aq) + 2e' —> Fe(s) §Zn2+(aq) + 2c" —> Zn(s) Page 19 onI r-u ‘4 Please Print Your Name (Family, First): , )Wmmwmwms .nww,wwvwmmw ” gMn2+(aq) + 2e" —) Mn(s) §A13*(aq) + 36' —> Al(s)> Em) + c” —_> “Li(s) Partial Periodic Table Physical constants c = 2.99792 x108m/s Physical constants K = 831447 J /(mol . K) N A = 6~02214><1023 “no! = 8.20578x10'2(atm-L)/(mol -K) e=1.60218x10"9C 1A=1C/S F=9.64853x104C/mol 1J=1VC h = 6.62607 x10'34J -s o __ RT Equations Ece" _ 5111K ln[A10 = kt , [A]: l = ~1—— 1 — kt 0 RT k = Ae' Ea/R" = 77;an Ecoell = Efathode _ Efnode S = k In W AG = "W = —nFE _ qrev max cell ASS-y: _ T AG0 2 —nFEcoe" AS111: = :roducts — Ensfuctants Page 20 of 21 .1 '4 ‘d n Please Print Your Name (Family, First): AHs s ASsurr = _ Ty S = k In W AGsys = Afisys «TASsys AS”): __ qrev T AG° =AH° —TAS° sys sys sys AG=—w AGO = ~RT1nK ASw" = - AG" =—RTan AG = AG” +RT1nQ Page 21 of21 ...
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