2010 Dec - UNIVERSITY OF TORONTO fi ' FACULTY OF ARTS AND...

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Unformatted text preview: UNIVERSITY OF TORONTO fi ' FACULTY OF ARTS AND SCIENCE DECEMBER EXAMINATIONS 2010 CHM l39Hl F Duration: 3 Hours NAME (print): Student Number: Lab Demo Group No.: Electronic calculators may be used; programmed calculators may not be used. A PERIODIC TABLE and USEFUL DATA are attached at the back of the exam. The Examination consists of a multiple choice component and a written answer component. Both the computer answer sheet and the exam paper must be handed in at the end of the exam. WHEN YOU RECEIVE YOUR EXAM PAPER AND COMPUTER ANSWER SHEET: 1. Write your name, student number and demonstrator group number on this page. 2. Write your last name and initials in the-box provided at the top right of the computer answer sheet. Blacken the appropriate circles for your last name and initials. 3. Write your student number along the top of the student number box and blacken the circles which correspond to your student number. 4. In the box titled FORM, fill in the circle marked 'A'. AT THE END OF THE EXAM: Insert your computer answer sheet into your test paper. Remain seated until all of the test papers have been collected. EXAMINER'S REPORT Total Part B PART A: Multiple Choice Questions There are 30 questions (1 mark each) for the multiple choice section of this exam. Your answers are to be recorded on the computer answer sheet and on this exam paper, both of which must be handed in at the end of the exam. Nothing written on the multiple choice section of this exam paper will be marked. The computer answer sheet MUST be filled in DURING the time allotted for the exam. 1. Clearly circle on the exam paper the letter corresponding to your choice for the best answer to each question. 2. Using a soft pencil (No.2 or softer), blacken the circle on the computer sheet which corresponds to the answer you have chosen for each question. Make sure that only one answer is blackened. Make no stray marks on the computer answer sheet. 1. Apple juice is an example of (a) a compound (b) an element (c) a homogeneous mixture ((1) a heterogeneous mixture 2. Elements A and Q form two compounds, AQ and A2Q3. The mass ratio (mass Q)/(mass A) for AQ is 0.286. What is the mass ratio (mass Q)/(mass A) for A2Q3? (a) 0.191 (b) 0.429 (c) 0.673 (d) 0.858 (e) There is not enough information to determine this. 3. A flask contains. 0.464 atm of oxygen gas. Ammonia gas is then introduced into the flask to a partial pressure of 0.132 atm at the same temperature. The ensuing reaction produces nitrogen monoxide gas and water vapour as the only products. Assuming that the reaction goes to completion, what will be the total pressure once the reaction is finished? (a) 0.596 atm (b) 0.629 atm (c) 0.330 atm (d) 0.662 atm (c) 0.518 atm 4. The number of orbitals in a given subshell, such as the 5d subshell, is determined by the number of possible values of (a) the angular momentum quantum number, 1. (b) the magnetic quantum number, m1. (c) the electron spin quantum number, ms. (d) the angular momentum quantum number, 1, and the magnetic quantum number, ml. (e) the magnetic quantum number, ml, and the electron spin quantum number, m. 2outof11 5. Of the following, which atom would you expect to have the smallest atomic radius? (a) Ga (b) Te (c) Sr (d) Mg (e) s 6. Which of the following statements about ionic compounds is true? (a) Essentially all pure ionic compounds are solids at room temperature and atmospheric pressure. (b) Ionic compounds do not contain any covalent bonds. (0) Ionic compounds contain the same number of cations as anions. (d) When dissolved in water, ions are solvated mostly by dipole-dipole interactions. 7. An unknown gas has a density of 3.164 mg/mL at 0°C and a pressure of 1 atm. What is the identity of the gas? (a) No2 (b) N204 (c) N306 (d) Cl2 (e) G62 8. In liquid trifluoroethane, F3C—CH3, which of the following intermolecular forces are present? (a) Hydrogen bonding forces only (b) Dipole-dipole forces only (c) Hydrogen bonding and dipole-dipole forces only ((1) Dipole-dipole and dispersion (London) forces only (e) Hydrogen bonding, dipole-dipole and dispersion forces are present 9. For the reaction mechanism shown below, which of the following statements is false? A + A 2;) C (fast equibrium) C + D —> E (slow) E + F —+ G + D (fast) (a) Doubling the concentration of A will quadruple the rate of reaction. (b) Doubling the concentration of D will double the rate of reaction. (c) Doubling the concentration of F will double the rate of reaction. (d) C is a reaction intermediate and D is a catalyst. (e) The overall net reaction is: 2 A + F —) E + G. 3outof11 10. The reaction Fe(phen)32+ + 3 H3O+ + 3 H2O —> Fe(H2O)62+ + 3 phenH+ has an activation energy of 126 kJ/mol. Its frequency (Arrhenius) factor has a value of 8.62 x 1017 5—1. At what temperature will the rate constant have a value of 3.63 x 10‘3 5—1? (a) 0°C (b) 50°C (0) 94°C (d) 367°C (e) 470°C 11. Lead metal is added to an aqueous solution that is 0.100M Cr3+ solution. What is the concentration of Pb2+ once equilibrium is established in the following reaction? Pb2+(aq) + 2 Cr2+(aq) 2:: Pb(s) + 2 Cr3+(aq) K= 3.1 x 109 (a) 8.2x 10*t (b) 9.3x 10*5 (c) 1.5x 104 (d) 7.3 x10‘3 (6) 1.5 x10—5 12. For the reaction 2 1C1(g) :2 Mg) + C12(g), a mixture of 0.749 atm of 12, 0.291 atm of C12 and 0.108 atm 1C1 are allowed to reach equilibrium, at which time the partial pressure of 12 is measured to be 0.542 atm. What is the equilibrium concentration of 1C1? (a) 0.522 atm (b) 0.379 atm (c) 0.083 atm (d) 0.207 atm (e) There is not enough information to determine this. 13. Which of the following chemical equations describes the reaction of water with the Bronsted-Lowry base HC2O4'? (a) Heidi—(act) + H200) :2 Czofiraq) + 0H“(aq) (b) HC204_(aCD + H200) 2:)— H2C204(aQ) + OH—(aQ) (c) H0204‘(aq) + OH'(aq) 7?- C2042‘(aq) + H20(aq) (d) HC2O4'(aq) + H2O(1) 2:). 2 CO2(g) + H3o+(aq) (e) HC2O4‘(aq) + H2O(1) 2:2 C2042‘(aq) + H30+(aq) 14. Aniline, C6H5NH2, is an important base with a Kb of 4.3 x 104°. What is the pH of an aniline solution made by dissolving 3.60 g of aniline in enough water to make 100.0 mL of solution? (a) 9.75 (b) 8.64 (c) 4.25 (d) 5.36 (e) 4.89 4outof11 15. The pH of a saturated aqueous solution of Mg(OH)2 is 10.35. The pH of the solution is then adjusted to 11.65. What is the solubility, in mol/L, of Mg(OH)2 after the adjustment of the pH? (a) 5.6 x10‘12 M (b) 1.2 x 10‘2 M (c) 2.8 x10'7 M (d) 7.5 x 1041 M (e) 4.3 x 10—10 16. Which species is oxidized in the following reaction? CuSO4(aq) + Fe(s) ——> FeSO4(aq) + Cu(s) (a) Fe (s) (b) CuSO4(aq) (0) Cu (5) (d) FeSO4(aq) 17. What is the relation between AG° and E° for the cell reaction below? Ni2+(aq) + Cd(s) ——> Cd2+(aq) + Ni(s) (a) AG° = F E° (b) AG° = 2 F E° (c) AG° = ——F E° (d) AG° = —2 F E° 18. Consider the galvanic cell: m I H2 (1 ann) I H* (1.0M) II 01' (1.0M) I Hg2c12(s) I Hga) Which one of the following changes to the cell would cause the cell potential to increase (i.e. become more positive)? (a) increase the mass of Pt (b) increase the pH (c) decrease the mass of Pt ((1) decrease the pH 19. When equilibrium is reached at constant temperature and pressure, (a) Q= 1. (b) AG° = 0. (c) S is maximized. (d) Gis minimized. 20. Calculate AH" for the reaction C3H8(g) + 5 02(g) —> 3 C02(g) + 4 H200) For the reaction: C3Hg(g) + 5 02(g) —) 3 C02(g) + 4 H20(g), AH° = —2046 kJ and the heat of vaporization of water is 44.0 kJ/mol. (a) —2222 kl (b) —2002 kl (c) —1870 k] (d) —2090 k] Soutofll 21. Find AE° for the reaction below if the process is carried out at a constant pressure of 1.00 atm and AV = —24.5 L. 2 00¢) + 02(g) —> 2 C02(g) AH° = —566. kJ (a) —564 kJ (b) —2.47 kJ (0) +2.47 k] (d) -568 kJ 22. The standard potential for the following galvanic cell is +0.90 V: 3 Cu2+(aq) + 2 Ga(s) 7—2 3 Cu(s) + 2 Ga3+(aq) The standard reduction potential for the Cu2+/Cu half-cell is +0.34 V. What is the standard reduction potential for the Ga3+/Ga half-cell? (a) +1.36 V (b) —0.56 V (c) —1.34 V (d) +0.56 v 23. Which is expected to have the most negative standard enthalpy of formation? (a) 02(g) (‘9) H200) (C) Hzcg) (d) H20(g) 24. For a process to be at equilibrium, it is necessary that (a) ASsys= —ASsurr- (b) ASsys = 03nd ASsurr = 0- (0) ASsys = ASsurr- (d) ASsys = 0- 25. What is expected when the reaction shown below takes place in a thermally—insulated container outfitted with a movable piston at a constant atmospheric pressure of 1 atm? 2C2H6(g) + 702(g) —> 4C02(g) + 6H20(g) (a) Volume will decrease and work will be done by the system. (b) Volume will decrease and work will be done on the system. (c) Volume will decrease and work will be done on the system. (d) Volume will increase and work will be done by the system. 6outof11 26. Which combination always results in a reaction being spontaneous? (a) AH is negative and AS is positive. (b) AH is positive and AS is negative. (0) AH is positive and AS is positive. (d) AH is negative and AS is negative. 27. Which of the following, under all conditions, depends only upon the initial and final state of a system? (a)w (b)q+w (c) w—AE (d) AE—w 28. Consider the reaction: N2(g) + 3 F2(g) —> 2NF3(g) AH" = —249kJand AS° = —278 J/K at 25°C Calculate AG° and state whether the equilibrium composition should favor reactants or products at standard conditions. (a) AG° = ——332 kJ; the equilibrium composition should favor reactants. (b) AG° = —166 kJ; the equilibrium composition should favor reactants. (c) AG° = —166 kJ; the equilibrium composition should favor products. (d) AG° = —332 kJ; the equilibrium composition should favor products. 29. The specific heat of copper is 0.385 J/(g -°C). If 34.2 g of copper, initially at 25°C, absorbs 4.689 kJ, what will be the final temperature of the copper? (a) 254°C 03) 381°C (0) 356°C (d) 27.8°C 30. Determine the sign of AS° for each of the following: I. C6H6(S) -> C6H6(l) H. 2S02(g) + 02(g) —> 2803(g) (a) AS° should be negative for I and positive for H. (b) AS° should be negative for I and negative for II. (c) AS° should be positive for I and positive for 11. (d) AS° should be positive for I and negative for H. 7outof11 PART B - Written Answer Questions There are 4 questions worth a total of 30 marks in this section of the exam. Clear and concise answers, which are essential for full marks, must be written in the spaces provided on the exam paper. Be sure to show your work. 1 (7 marks). The sap in a maple tree can be described as a 3.0% (by mass) solution of sucrose, C12H22011, in water. Sucrose does not dissociate to a significant extent in ' aqueous solution (a) At 20°C, the density of sap is 1.010 g/cm3. Calculate the molarity of sucrose in sap. (b) Each year, a typical maple tree yields approximately 45L of sap. How many molecules of sucrose are contained in this volume of ? (c) The rising of sap in trees from their roots to their highest branches is caused largely by osmosis. The osmotic pressure arises from the concentration of dissolved sucrose in sap being higher than that of the (almost) pure water outside the tree. Determine the osmotic pressure of the sap solution at 20°C. To what height would a vertical column of sucrose be supported by the osmotic pressure which you have calculated? Compare this height to that of an average tree (say, 15m). Soutofll 2 (8 marks). Aspirin is a monoprotic organic acid with Ka = 3.3 x 10-4. 0.112g of aspirin was dissolved in 20.00 mL of water. When this solution was titrated with 0.0200M NaOH, the equivalence point was reached after the addition of 3 l .08 mL of titrant. ' (a) Determine the molar mass of aspirin. (b) What is the pH at the equivalence point of the titration? (c) Would you expect aspirin or its sodium salt to be mOre soluble in water? Provide an explanation for your choice. 9outofll 3 (7 marks). Consider the following gas-phase reaction of A2 molecules (black) with B2 molecules (white): A2(g) + B2(g) 2:: 2AB(g) AG° = 15 k] (a) Which of the following reaction mixtures (1, 2 or 3) will have the smallest AG of reaction? Provide an explanation for your choice. (b) Ifthe partial pressure of A2 in reaction mixture (3) is equal to 1 atm, what is the value of AG for the reaction in mixture (3)? Please be sure to show your work. (0) Show how the Gibbs free energy change for a process taking place at constant temperature and pressure can be derived fiom the second law of thermodynamics. 10 out ofll 4 (8 marks). Consider the arrangement of two half-cells shown below: (a) Complete the drawing by adding any components essential for a functioning cell. (b) Label the anode of this cell and indicate the direction of ion flow. (c) Write a balanced equation for the cell reaction. (d) A student cuts the wire and inserts a voltage source. At standard conditions, what voltage does she need to apply to reverse the direction of electron flow? -—ENDOFTHEEXAM— lloutofll CHM 139H: Equations for the CHM139 Final Exam E=hv c=/1V l=—h— AxA(mv)2£ mv 4n _ —1s En=_g'_.18..x_219__{ PVanT n nZa _3 1/2 [P+—VT (V—nb)=nRT Ekz‘n _ uavg PA = XAPj ATb =Kbcm ATf=—Kfcm H=MRT —bi 2—4 V=4 7tr3 For ax2+bx+c=0, x=————b——~a—c- 3 2a id __ L- 1 = _ _ Ea 1n[[A]0 _ kt [A] [AL kt [A]—-[A]o—kt 1nk—1nA—RT KP = KC(RT)A" pH = pKa +104[[1%1]]] Physical and Chemical Constants Avogadro’s number Boltzmann’s constant Fundamental unit charge Zero point Gas constant Density of dry air (at 00 C and 1 atm) Heat capacity of water Density of water (at 25°C) Density of mercury (at 25°C) Planck’s constant Speed of light Rydberg’s constant Acceleration due to gravity Ion-product constant of H20 (at 25°C) NA = 6.0221367 x 1023 mole'1 k = 1.380658 x10'23 J K'1 e =1.60217733 x10"19 C 0°C = 273.15 K R = 8.314510 J mole'l K'1 = 0.082058 L atm mole'l K'l 1.292 x 10'3 g mL'1 8 =4.184 J g" K'1 = 75.4 J mol'lK'1 0.997 g mL'1 13.6 g mL'1 h = 6.6260755 x 10'34 J s c = 2.99792458 x 108 m s'1 R. = 1.0974 x 107 m‘1 g = 9.80 m s'2 Kw = 1.00 x10"14 Conversion Factors 1 a.m.u. = 1.6605402 x 10'27 kg 1 atmosphere (atm) = 1.01325 x 105 Pa = 760.0 mm Hg (torr) = 1.01325 bar 1 calorie (cal) = 4.184 joules (J) 1 debye (D) = 3.335617 x 1030 C m 1 eV/particle = 96.485 kJ mole“ = 23.061 kcal mole'l 1 eV = 1.602 x 10'19 J = 8067 cm'1 1 kcal mole'1 = 4.184 kJ mole‘l = 349.73 cm'1 1 kJ mole'l = 0.23901 kcal mole'l = 83.591 cm" 1 L atm= 101.325 J = 24.217 cal In x = 2.3026 log x 7t=3.1415927 Standard Reduction Potentials (in Volts at 25°C) é Reaction C12 + 2e‘ —> 2C1‘ 02 + 4H+ + 4e‘ —> 2H20 +1.36 +1.23 +1.07 Brz + 26' —> 2Br‘ Fe3+ + e— —-> Fe2+ +0.77 Ag+ + e" —) Ag +0.80 Cu+ + e’ —) Cu +0.52 Fe(CN)63’ + e— —> Fe(CN)64‘ +0.36 Cu2+ + 2e' —9 Cu +0.34 +0.15 Cu2+ + e" —) Cu+ Sn4+ + 2e‘ —> Sn2+ +0.15 2H+ + 2e‘ —> H2 Fe3++3e‘ —> Fe Pb2++2e‘ —> Pb C02++2e_ —) Co Fez++2€f —) Fe Cr3++3e— —> Cr an +2e‘ —9 Zn 2 H20 + 2 e“ —> H2(g) +2 OH" —0.83 V2+ + 2e‘ —) V —1.18 Mn2+ + 2e‘ —-) Mn —1.18 A13+ + 35 —> A1 —1.66 Mg2+ + 2e‘ —-) Mg —2.37 1 100794 Periodic Table of Elements ‘8 H 2 4.002602 Hydrogen ©1998-2000 Reid-it Limited He Hell 1 3 14 15 1 6 1 7 um 5 10.811 6 12,011 7 14,007 8 15.999 9 18.998 10 20.180 B C N 0 F Ne Boron Carbon Nitrogen Oxygen Fluorine Neon AI P S Cl 13 26.98214 28.08615 30.97416 32.06617 35.45318 39.948 Transition Elements 4 5 6 7 8 1 2 Phosphorus Argon 47.87 23 50.942 24 51.996 25 54.938 26 55.845 30 65.39 33 74.922 34 78.96 35 79.904 36 83.80 Ti V Cr Mn Zn As Se Kr Vanadiu Chromium Manganese Zinc Arsenic Selenium Krypton 112.41 49 121.76 52 127.60 53 126.90 54 131.29 Cd Te l Xe y Iodine Xenon 85 [209.99] 86 [2202] At Rn AstaIine Radon [293] Uuo 55 132.9156 137.33 57 12851 Uuq Ununquadium [289] Uuh Ununhexium Halogens Ununoctium Aékft'gne Noble Gases a S Alkali Metals Key 95 [24106196 [247] 97 [247.07] 93 [251.08] 99 [252081100 [257.10] 101 [258.10] 102 [259.10] 103 [262.11] atomic no. Am cm [masst longest ived isotope] Americiun Curium ‘ ' ‘ ' ‘ ' ' ' Element Symbol Actinides name (name: historical or altemative name) ...
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2010 Dec - UNIVERSITY OF TORONTO fi ' FACULTY OF ARTS AND...

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