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2011 May - UNIVERSITY OF TORONTO FACULTY OF ARTS AND...

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Unformatted text preview: UNIVERSITY OF TORONTO FACULTY OF ARTS AND SCIENCE APRIL EXAMINATIONS 2011 CHM 139H1 5 Name (print): Student NO: Demonstration Gp. No.: DURATION: 3 HOURS TOTAL MARKS = 67 Calculators may be used but not shared. Programmable calculators may not be used. A PERIODIC TABLE and USEFUL DATA are attached to the back 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’. YOUR ANSWERS ARE TO BE RECORDED ON THE COMPUTER ANSWER SHEET AND ON THIS PAPER BOTH OF WHICH MUST BE HANDED IN AT THE END OF THE EXAM. AT THE END OF THE EXAM: Insert your computer answer sheet into your exam paper. Remain seated until all exam papers have been collected. mm- TOTAL (PART A) = [30 EXAM TOTAL = /67 Page 1 of 17 PART A: MULTIPLE CHOICE QUESTIONS (1 mark each) 1. In an experiment 200 g of A when mixed with 300 g of B gives 500 g of C. In another experiment, 30.0 g of A is mixed with 50.0 g of B. How many grams of C will be formed? a) 30g b) 55g c) 75g d) 80g e) 83g 2. What is the pressure of the gas in the bulb? 3) Pgas = P h b) Pgas = Patm C) Pgas = Ph + Patm d) P gas = Ph " Patm e) Pgas = Patm _ Ph 3. Which statement below is incorrect? a) A 15 orbital is smaller than a 35 orbital. b) A 35 orbital has three spherical nodes. c) A 2p orbital has one nodal plane. d) A 3p orbital has one nodal plane. e) A 3d,: orbital has four lobes. 4. At what temperature will sulfur hexafluoride molecules have the same average speed as argon atoms at 20°C? a) -22°c b) 732°C c) 381°C (:1) 568“C e) 799°C 5. Considering the graph on the right, which statement is true? a) Boiling point ~120°c. 3? b) Boiling point ~95°c 5 8° c) Boiling point "75°C E °°' d) Melting point ”95°C 3 4°' e) Melting point "75°C. 320' > 0° 25 so 75 100 Temperature ("6) Page 2 of 17 6. Which one of the following decreases as the strength of the attractive intermolecular forces increases? a) the heat of vaporization. b) the normal boiling point. c) the extent of deviations from the ideal gas law. d) the sublimation temperature of the substance. e) The vapour pressure of liquid. 7. This is the phase diagram for iodine. Which of the following transitions occur when the temperature and pressure conditions are changed from A to B to C to D? a) l—->s—>g—->l b) s—)l—->g—->s c) g-—>s-—>l—>g d) s——>l—>g—>|—>s e) s—)g—>|—)g——>s "we ”we r. New " Tit-mam 8. At 80°C, pure liquid A has a vapour pressure of 700 mm Hg and pure liquid B has a vapor pressure of 940 mm Hg. What is XA for a solution of A and B with a normal boiling point of 80°C? a) 0.25 b) 0.45 c) 0.50 d) 0.75 e) A solution of A and B cannot boil at 80°C. 9. The rate constant for a first-order reaction is k = 0.00073 5“. Determine the percent of reactant that has decomposed after 300 s. a) 80% b) 63% c) 37% d) 20% e) 15% 10. The rate of a specific chemical reaction is independent of the concentrations of the reactants. Thus the reaction is: a) first order b) second order c) exothermic d) catalyzed e) none of these Page 3 of 17 i“ 11. What is the rate law for the following mechanism 12. 13. 14. CH3COOC2H5 + H20 9 CH3COOC2H5+ + OH' (Slow) CH3COOC2H5+ —> CH3COOH + C2H5+ (Fast) C2H5+ + OH' -> C2H50H (Fast) a) Rate = k[CH3COOC2H5][H20]2 b) Rate = k[CH3COOC2H5][H20] c) Rate = k[C2H50H] d) Rate = k[CH3COOC2H5+] e) Rate = k[CH3COOC2H5] Given the following reactions, 2PCl3(g) : 2P(g) + 3Cl2(g) Kc = 0.0667 PCl3(g) + Clzlg) .——= PClslg) Kc = 4.00 Calculate Kp for the reaction below at 250°C. 2P(g) + 5C|2(g) ‘7‘- 2PC|5(g) a) 2.57x10-15 b) 2.74x10'5 c) 0.267 d) 60 e) 240 Starting initially only with reactants, the following reaction, 2 N02(g) ‘-—‘ 2 N0(g) + 02(g), reaches equilibrium. At equilibrium, the partial pressure of 02(g) 0.3500 atm and PW, = 1.0866 atm. What is Kp for this reaction? a) 0.350 b) 2.86 c) 66.9 d) 128 e) 182 The half equivalence point in the titration of 0.100 M CH3NH2 (Kb = 3.7 x 10“) with 0.250 M HCI occurs at pH = a) 3.43 b) 4.21 c) 5.72 d) 8.35 e) 10.57 Page 4 of 17 15. 16. 17. 18. 19. Calculate the solubility (in g/L) of calcium fluoride in water at 25°C if the KSp for Can is 1.5 x 10'“). a) 9.6 x 10-4 g/L b) 2.6 x 10-2 g/L c) 3.3 x 10-2 g/L d) 4.1 x 10-2 g/L e) 5.3 x 10-2 g/L The following are all examples of different forms of energy with the exception of: a) chemical b) dynamic c) electrical d) kinetic ' e) thermal Consider the notation AX“, where X is any state function. The ° symbol denotes that substances are in their stable form at 1 atm pressure (1 M concentration for solutes), and that: a) The units of temperature must be °C and not K b) The value ofAX" is reserved (AX = Xmma. —Xflna.) c) The value ofAX‘ is independent of temperature d) The value of AX“ is for a specific temperature What is the value of AG for the following reaction at 25°C if AG° = -1335 kJ/mol and PH, = Q4 atm, PBrz = 0.08 atm, and PHBr '-' 1.6 atm? Hzlg) + Brzlg) = 2 HBrlg) a) —127.6 kJ/mol b) -137.6 kJ/mol c) -128.8 kJ/mol d) -149.3 kJ/mol e) -153.5 kJ/mol A common test for the presence of water vapour is cobalt chloride paper, which turns from blue to pink according to the equilibrium reaction: COCI: (5) + 6 H20 (g) :3 CO(H20)5CI2 (5) Given that AH” = ~352 kJ/mol and AS° = —899 J/(K-mol) at 298 K, AG“ and Kfor this reaction are: a) A6" = —2.47 kJ/mol and K = 3.56 x 10'8 b) AG° = —36.7 kJ/mol and K = 6.73 x 10‘4 c) A6“ = -56.2 kJ/mol and K = 9.14 x 109 d) A6“ = -84.1 kJ/mol and K = 5.52 x 1014 e) AG° = —649.9 kJ/mol and K = 6.08 x 10113 Page 5 of 17 20. What is the total heat of reaction when exactly one mole of glucose (C5H1205) is burnt completely 21. to yield carbon dioxide gas and water vapour under conditions of constant pressure (1 atm) and temperature (298 K)? M M a) -2552 kJ/mol b) -1286 kJ/mol c) -19 kJ/mol d) +652 kJ/mol e) +843 kJ/mol If a reaction vessel becomes warmer as consequence of a reaction, which of the following must . be true? 22. 23. a) the reaction is endothermic b) the reaction is nonspontaneous c) the surroundings absorbs heat from the system d) AH is positive e) work is done on the system What is the entropy of the disordered state of a crystal of 100 molecules of BF3, if each trigonal planar molecule is oriented randomly in one of three possible ways? a) 5.05 x 10‘22 J/K b) 1.91 x 10'22 J/K c) 6.36 x 10'231/K d) 1.52 x 10'211/K e) 2.12 x 10‘231/K The reaction A 9 B is spontaneous. The graph below depicts the free energy of the system as a function of a mixture of various concentrations ofA and B. At which position(s) on the graph (if any) will the reaction spontaneously form more molecules of A than B? a) land II b) ll and III C) III only d) ll only (5 e) none of the above < [A] = 1 [A] = 0.5 [A] = 0 [B] = O [B] = 0.5 [B] = 1 Page 6 of 17 24. The reduction of benzoquinone (Bq) to hydroquinone (BqHz) can be used as a godel for many enzymes that exploit similar compounds in their active sites. Given the following standard reduction potential, what would the electrode potential be for the same reaction at pH 7.40 and 37 “C, given concentrations of 0.100 M for both Bq and BqHz? Bq+2H*+2e'—->BqH2 E°[email protected]°C a) E = +0.111 V b) E = +0.259 V c) E = +0.280 V d) E = +o.4o7 v e) E = +0.555 V 25. A galvanic cell is constrUCted of the following components: a solid Cu electrode in a 1.00 M aqueous solution of CuSO.., 3 salt bridge containing KNOg, a solid scandium electrode in a 1.00 M aqueous solution of Sc(N03)3, and a digital voltmeter. Sc3+(aq) + 3e" 9 Sc(s) E ° = —2.09 V Cu2+(aq) + 2e‘ 9 Cu(s) 5° = +0.34 v The meter is connected so as to give a positive value of the cell potential when operated at 25.0“C. For this cell, it is true that: a) Diluting only the Cu2+ solution will decrease the cell potential b) Diluting only the Sc3+ solution will decrease the cell potential c) Diluting both solutions by the same amount has no effect on Em" d) Adding KN03(s) to either half-cell will change the cell potential 26. The following statements about the role of the salt bridge in a galvanic cell are all true with the exception of: a) The salt bridge connects the tw0 half-cells. b) The salt bridge completes the electrical circuit. c) It allows non—reacting ions to migrate between half-cells. d) It stops electrons from migrating through the solution. e) It helps maintain electrical neutrality of the solutions. 27. Which two of the following half-reactions will combine to give the galvanic cell with the highest cell potential? I Cu2*(aq) + 2 e‘ 9 Cu(s) u Ni2*(aq) + 2 e' a Ni(s) Ill C|2(s) + 2 e' 9 2 Cl'(aq) IV Mgz*(aq) + 2 e' 9 Mg(s) a) l and IV b) n and IV C) III and N d) land lll e) II and III Page 7 of 17 « 28. Which of the following is the best shorthand notation describing a galvanic cell in which Mn04' 29. 30. (aq) is reduced to form Mn2*(aq) in one half-reaction, and copper metal is oxidized to form Cu2+(aq) in the other half-reaction? al PtiS) l Mn04‘iaql. an‘iaq) ll Cu($l l Cuz‘iaql b) CUlS) l Cuz‘laq) ll Mn04'laq), Mn2*(aq) l Pt($) C) Cu2+laql l CU(Sl ll Mn“(aql l Mn04'laq) d) Mn04'laql. Mn2*(aq) ll CU(5) l Cuz‘laq) e) MS) I Cuz‘laq) ll Fe3*(aq). Fez‘iaql l Pt($) Which of the following is the best solution to overcome the problem of oxidative corrosion of Hon? 3) Allow rust (F8203) to form around the iron, which serves as a water-tight barrier, stopping the process from continuing b) Store the iron in an atmosphere with high oxygen content, which slows the rusting process c) Store the iron under water with dissolved salts, which prevents the reaction from taking place d) Put the iron in contact with a metal with high E0, to serve as a sacrificial anode e) Put the iron in contact with a metal with high Ered to serve as a sacrificial cathode 4.47 g of aluminum metal was plated out by passing current through a solution of Al(N03)3 for 10 minutes. What current was used in this electroplating reaction? a) 26.7A b) 120.0A c) 4796.0A d) 1600.0A e) 80.0A Page 8 of 17 PART 8. SHORT ANSWER QUESTIONS: Answers must be written in pen in the boxes provided. Be sure to show your work. 1. (11 marks) Every year, oral rehydration therapy (ORT) saves the lives of countless children worldwide who become severely dehydrated. One requirement of the solution is that it be isotonic with human blood. (a) One definition of an isotonic solution is that it has the same osmotic pressure as 0.92 % NaCl (aq) (mass of solute (g)/vo|ume of solution (mL)) at room temperature. Calculate (i) the osmotic pressure and (ii) the molality of this solution. Assume the solution’s density to be 1.00 g/mL, and the van’t Hoff factor for NaCl to be 2. (b) Another definition is that the solution has a freezing point of —0.52 'C. Show that these two definitions are in reasonably close agreement. Page 9 of 17 m (c) Use the freezing point definition (part b) to show that an ORT solution containing 3.5 g NaCl (FW = 58.44 g/mol), 1.5 g KCl (FW= 74.55 g/mol), 2.9 g Na3C6H507 (sodium citrate, FW= 258.07 g/mol), and 20.0 g C5H1205 (glucose, FW = 180.2 g/mol) per liter meets the requirement of being isotonic. Some of you might recall that some salts have acid-base properties. Please ignore those when answering this question and assume that all salts are completely dissociated in solution. Page 10 of 17 2. (8 marks) (a) The pKa of hypochlorous acid (HOCI) is 7.49. Calculate the pH and the percent dissociation in a 0.10 M solution. (b) If 1L of 0.10 M solution of HOCI is titrated with 300 mL of 0.20 M NaOH, what is the final pH of that solution? (c) In one experiment, a 40 mL solution of 0.10 M HOCI is titrated with 0.100 M NaOH. In a separate experiment 40 mL-of a 0.10 M hydrochloric acid (HCI) solution is titrated also with 0.100 M NaOH. On the graph below sketch qualitatively the two titration curves. l4 1 2 10 pH 6 4 2 0 0 20.0 40.0 60.0 80.0 mL of 0.100 M NaOH added Page 11 of 17 3. (10 marks) The following information is available about the reduction of silver oxide (all standard values at 25 °C): AgzO(5) —> 2 Agls) + V2 02(g) Ag20(5l Agls) ozlg) m (kl/mo. —.z_-m_ moo/mm (a) Calculate AH' at 25 °C for this reaction (show your work): (b) Calculate AS° at 25 °C for this reaction (show your work): (c) Calculate AG° at 25 °C for this reaction (show your work): (d) At what temperature is this reaction in equilibrium (show your work)? . (e) Would the addition of a catalyst move the equilibrium position of this reaction at 25 “C? Briefly state why or why not: Page 12 of 17 4. (8 marks) Consider the galvanic cell depicted below. Assume standard temperature and pressure. (3) Write the balanced reaction equation and shorthand cell expression for this cell. (b) What is the equilibrium constant for this reaction? (c) What is AG” for this reaction? (d) What is Ece" if the ions that participate in the reaction at the cathode are present at 10 M concentration, and ions that participate in the reaction at the anode are present at 0.001 M? Page 13 of 17 USEFUL EQUATIONS E=hv =c/v A=h/mv Ephoton=hvo + Ek E, = - Rsz/n2 PV=n RT (P+nza/V2)(V-nb)=n RT KE = V2 mu2=3RT/(2NA) urms = (3RT/M)“2 A T}, = K bm A Tf = K fr" n =M RT Psolution=XsolventPsolvent —bi-\/b2 -4ac Za ax2 + bx + c = 0 X= ln(ab) = ln(a) + ln(b) ; ln(a/b) = -ln(b/a) Kp=Kc(RT)A”; An = c + d - (a +b) Arrhenius equation: k = Ae’Ea/RT |"(:_2]=(L:_=)[_T1__$1.] First order reaction: ln{[A]o/[A]} = kt Second order reaction: 1/[A] — 1/[A]o = kt Zero order reaction: [A]: -kt + [A]o pH = -log[H30+] pOH = -log[0H'] pH + pOH = 14 Kax Kb = KW q=nCAT w=—PAV AE=q+w AH=AE+PAV $=kan 5:; A'Suniv=A'S-'_A'§;surr AH" = Z coefprH; (pdts) — ZcoeffiAH; (rcts) A5" = 2 coeffp$° (pdts) — Z coefifiS" (rcts) AG" = Z coeji‘jjJAG}a (pdts) — Z coefiflAG} (rcts) AG = AH—TAS AG=AG°+RT|nQ AG=—nFE E=E°-EI—an I=-’£ nF t Page 14 of 17 PHYSICAL AND CHEMICAL CONSTANTS Atomic mass unit Mass of an electron Mass of a neutron Mass of a proton Avogadro’s number Boltzmann’s constant Faraday’s constant Fundamental unit charge Gas constant Heat capacity of water Planck’s constant Rydberg’s constant Speed of light Zero point KW of H20 at 25°C Pi CONVERSION FACTORS 2.54 cm = 1 inch 1 N = 1 kg m s’2 1 kg = 2.205 pounds (lbs) 1 nm = 10'9 m 1 A = 10‘10 m 1 Watt = 1 Joule sec"1 1 Amp = 1 C/s 1 a.m.u. = 1.6605402 x 10‘27 kg me = 9.109 x 10'31 kg mn = 1.674 x 10'27 kg mp = 1.672 x 10'27 kg NA = 6.0221367 x 1023 mole‘1 k8 = 1.380658 x 10231 K“1 F = 9.6485309 x 104 c mole"1 e = 1.60217733 x 10'19 c R = 8.3145101 mole‘1 K‘1 = 0.082058 L atm mole‘1 K'1 s = 4.1841 g'1 k1 = 75.41 mole:1 K'1 h = 6.6260755 x 10341 s RH = 2.1798 x 10181 = 1.097 x 10'2 nm‘1 c = 239792458 x 108 m s'1 0°C = 273.15 K 1<w = 1.00 x 10'14 n = 3.1415927 1 atmosphere (atm) = 1.01325 x 105 Pa (N m'z) = 760.0 mm Hg (torr) = 1.01325 bar 1 calorie (cal) = 4.184 joules (J) 1 debye (0) = 3.335617 x 103°C m 1 eV/particle = 96.485 kJ mole'1 = 23.061 kcal mole”1 1 eV = 1.602 x 10491 = 8067 cm'1 1 kcal mole'1 = 4.184 k1 mole'1= 349.73 cm'1 1 k1 mole‘1 = 0.23901 kcal mole'1= 83.591 cm‘1 1 L atm = 101.325) = 24.217 cal In x = 2.3026 log x Page 15 of 17 LI 40 91 932d PE RIOIIC TABLE OF THE ELEMENTS . http://wwmkylapliLhr/pefiadui/en/ 2 4.0026 swarm!” cnflmmmmsmw He “’“RECSM‘WM’QN “/mmwfisusim CE 13 NA 14 [VA 15 VA 16 VIA 17 VIIA Heuuu 13 "IA - .160 ATOMICNUMBER 5 10.311 mmcmsa) 5 10.811 6 12.011 7 14.007 8 15.999 9 18.998 10 20 B C N 0 F Ne . ' canon CARBON NITROGEN OXYGEN FLuomNE NEON , WNW 13 26.902 14 28.086 17 35.453 “"3 > P S Cl Ar VB ,6 VIB 7 VIIB 8 i 9 10l I; 8311 ‘ . 'PHOSPHORUS smua 016.0301: mam .28 58.693 29 68.646 30. 65.30. .31 09.723 32 72.64. N1 Cu ‘ ' ' 57% “‘1' 01995-2002 Ean. I'll .. l D“ --. M46 64 15725 65 150.93 .66 162.50 67 164.93 68 167.26 69 168.93 70 173.04 71 174.07 1 ,, »’ Gd H0 Er 1 Tm Yb Lu 1 SAMARIUM EUROPIUM GADOUNIUM TERfllUM HOLMIUM ERBIUM THUUUM YTTERBIUM LUTEflUM 94 1244), 95 (243) 96 (247) 97 (247)" 98‘ (251) 99 (252) 100' (257) 101 (258) 102 (259) Pm Am Cm (If Es Fm Md N0 NEPTUNIUM PLUTONIUM AMERIGYUM CURIUM BERKEIJUMCAUFORMUMEINSTEINIUM EERMIUM WNW NOBELIUM LAWRENGIU (1) mwawn..nuo.4, 6614663 (2001) Mam,mb m n M14391 53:6 dydleWI-‘ormhlxmm- \ mumummdmmmm WWW! CERIUM mumem . “mmm»mm.mm~0) ' ' m . . . Ammue mmmwammmwudfl: W. Edit): AflyaVaflhm (Wm) Standard Reduction Potentials (in Volts), 25°C Fe(CN)63' + e' ---> Fe(CN)64' _- Cu2+ + 2e' ——-> Cu Cu2+ + e' ---> Cu+ +0.15 Sn4+ + 2e' ---> Sn2+ +0.15 2H+ + 2e' ---> H2 Fe3+ + 3e' ---> Fe Pia2+ + 2e" --—> Pb -o.13 le+ + 2e’ ---> Ni -0.26 Fe2+ + 2e' —--> Fe -0.41 'Cr3+ + 3e' ---> Cr -o.74 2n2+ + 2e' --—> Zn -0.76 2H20 + 2e’ ---> H2(g) + 20H' -O.83 v2+ + 2e' --—> v -1.18 Mn2+ + 2e’ ---> Mn -1.18 AI3+ + 3e" ---> Al -1.66 Mg2+ + 2e' ---> Mg -2.37 Page 17 of 17 ...
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