CHM140Y5Y05 Exam - Name: _—__.._..______ Student Number:...

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Unformatted text preview: Name: _—__.._..______ Student Number: UNIVERSITY OF TORONTO AT MISSISSAUGA Erindale College AprillMay Examinations 2005 CHM140Y Duration — 3 hours Aids Allowed: non-programmable calculators only Notes to students: Enter your name and student number on each page of the examination paper before beginning the examination. Answer 8 questions (out of 10). Each question counts for 20 marks (which is also the time allotted per question in minutes). CIRCLE BELOW THE NUMBER OF THE 2 QUESTIONS THAT YOU DO NOT WANT TO HAVE MARKED. IF YOU DO NOT DO THAT, WE WILL ONLY COUNT THE MARKS FOR THE FIRST 8 PAGES ON WHICH THERE IS WRITING. 1 II Atomic Masses: H = 1.008, 0 = 16.00, N = 14.01, Mg = 24.30, Cu = 63.55 van der Waals constants for H20: 3 = 5.46 atm L2 mol'z, b = 0.0305 L mol‘l R = 0.08205 L atm K"1 11101" = 8.314 J K'1 mol'l N = 6.022 x 1023 molecules mol'1 1] = 6.626 x103“l J S c = 3.00 x 105 ms—1 continued on page 2 CHM140Y page 2 of 11 Name: ______._._.____.——-— Student Number: 1. a. Nitrogen gas can be prepared by passing gaseous ammonia over solid copperfll) oxide at high temperatures. The other products of the reaction are solid copper and water vapour. If 18.1 g of NH3 are reacted with 90.4 g of CuO, how many grams of N2 will be formed? ' b. An element is a mixture of two isotopes. One isotope of the element has an atomic mass of 34.96885 mm and has a relative abundance of 75.53 % in nature. The other isotope has an atomic mass of 36.96590 amu. Calculate the weighted average atomic mass and identify the element. c. Which aqueous solution will have the higher boiling point, 0.5 M NaCl or 0.5 m NaCl? Briefly explain. continued on page 3 CHM140Y ‘ page 3 of 11 Name: w__.__— Student Number: 2. a. Consider the flasks shown below. What are the final partial pressures of H2 and of N2 (in atm) after the stopcock between the two flasks is opened? (Assume that the final volume is 3.00 L.) 2.00 L 1.00 L 475 torr 0.200 atrn H2 N2 b. Calculate the pressure exerted by 2.000 mol H20 in a 1.0000 L container at 25°C, (1) using the ideal gas law and (2) using the van der Waals equation. Comment briefly on why the results of the two calculations are different. continued on page 4 CHM14OY page 4 ofll Name: ____—_....___— Student Number: 3. a. At what temperatures will each of the processes with the following values of enthalpy changes and entropy changes he spontaneous? Briefly explain any calculations. (1) AH = -25 k], AS = —5.OJK_1 (2) AH = +25 kJ, AS = +5.0J K.—1 (3) Ali 2 +25 kJ, AS = -5.0 J K‘1 (4) AH = —25 kJ, As = +5.0J K4 b. Write the balanced equation for the dissolving of Mg (5) in HCIW. How much work is done when 50.00 g of Mg“) is dissolved in excess HCIW in a container of flexible volume at a constant temperature of 23°C? Assume ideal gas behaviour. ' continued on page 5 CHM14OY page 5 of 11 Name: _._.__.__...__—_ Student Number: 4. a. It takes 7.21 x 10—” J of energy to remove an electron from an iron atom. What is the maximum wavelength of light that can do this? b. What is the maximum number of electrons in an atom that can have these sets of quantum numbers? Explain very briefly. (1) n=0,1=0,m=0 (2) n=2,l==1,m=—1,s=*1/2 (3) n=3 (4) n=2,l=2 (5) n=1,l=0,m=0 c. Three elements have the following electron configurations: 1322322p63523p6 1s12s22p6382 1522s22p63s23p64s‘. The first ionization energies of these elements (but not necessarily in the same order) are 0.419, 0.735 and 1.527 M] mol—l. The atomic radii of these elements (also in random order) are 160, 98 and 235 pm. Identify the three elements and match the appropriate values of ionization energy and atomic radius to each electron configuration and element, (1. Give two positive ions and two negative ions that are isoelectronic with argon. Write these ions in order of increasing size, smallest first. continued on page 6 CHM140Y page 6 of 11 Name: _—___.___—_..__ Student Number: 5. For each of the following molecules or ions: a. classify it according to the AXE nomenclature of the VSEPR theory, b. name the molecular shape, c. draw a three-dimensional structure showing all valence shell electrons of all atoms and any formal charge that exists, d. name the type of hybrid atomic orbitals used by the central atom for sigma bonding. AXE claSSIficanon name of molecular shape three dimensional structure b. Draw the three possible Lewis structures for nitrous oxide, N20, showing all valence shell electrons and any formal charges (N is the central atom). Refer to the table of average bond lengths below and explain what you would expect the NN and the NO bond lengths to be in nitrous oxide. N-N 167 pm N—O 147 pm N=N 120 pm N=O 115 pm NEN 110 pm continued on page 7 CHM140Y page 7 of 11 Name: —_ Student Number: 6. a. Derive the equations that show that while the half—life for a first order reaction is independent of the original reactant concentration, the halfalife for both zero—order and second-order reactions depends on the original reactant concentration. b. The radioactive isotope 3’ZP decays according to first—order kinetics and has a half-life of 14.3 days. How long does it take for 95.0% of a sample of 32F to decay? continued on page 8 CHM14OY page 8 of 11 Name: ___________._____._ Student Number: 7. For the reaction CH3OH + Br‘ -* CH3Br + OH‘ the following two mechanisms have been proposed. (1) (2) CH3OH + OH‘ # CH3O' + H20 fast CHSOH + H3O+ <-—‘ CH30H2+ + H20 fast CH3O" + Br" —’ [BrCH3O_2] slow CH3OH2+ 4- Br‘ ‘+ [BICH3OH2] slow [BrCH3O“2] -> CH3Br + 0—2 [BrCH3OH2] -> CHsBr + H20 fast 0—2 + H20 -> 20H“ 2H20 # H3O+ + OH— fast a. What would you expect the rate law to be for each of these mechanisms? Show how you figure this out. b. Briefly explain how one could experimentally distinguish between the two mechanisms. c. Briefly explain which mechanism you think is most likely to occur. d. Consider mechanism (2). If the observed rate constant is 191le = 1.6 x 10_“sec‘1M_2 and the reaction is carried out with [CH3OH]0 = 0.5M, [mono : 0.5M, and [Br"]o = 4 x 10‘5M, how long will it take to reduce the [Br‘] to 4 x 10’6M? continued on page 9 CHM140Y page 9 of 11 Name: —._______._— Student Number: 8. a. Calculate the value for the equilibrium constant, for the reaction 02(g) + 0(g) ‘1‘ 03(g) given the equilibrium constants for the reactions N02 (g) rt- NO (g) + 0 (g) KP = 6.8 x10~49 and 03 (g) + No (Q ‘1‘ N02 (3) + 02 (g) Kp = 6-8 X 10.34- b. The reaction 2H20 ~——‘ H3O+ + OH“ is endothermic. Will the pH of pure water at 60°C be less than, equal to, or greater than 7.0? Briefly explain. c. Assume that the reaction for the formation of gaseous hydrogen fluoride, Hz(g) + thg) r-‘ 2HF(g) has an equilibrium constant of 1.15 x 102 (at a certain temperature). In a particular experiment, 3.000 mol of each component was added to a 1.500 L flask. Calculate the concentrations of all species that exist when equilibrium is established. continued on page 10 CHM140Y page 10 of 11 Name: — Student Number: 9. A 2500 mL sample of 0.1002 M lactic acid, a monoprotic acid, was titrated with 0.1997 M NaOH. 3. When about 6.25mL of base were added, a buffer solution resulted. Explain. b. When a total of 10.00n1L of base were added, the pH was 4.46. Using the simultaneous equations method, calculate the KA of lactic acid. c. Calculate the pH at the equivalence point of the titration. Be sure to explain any simplifying assumptions made in your calculations. continued on page 11 CHMl40Y page 11 ofll Name: —.______._____.._.____ Student Number: 10. a. Write a series of reactions showing how 2,3—dimethylbut-2-ene could be synthesized from propan—2—01 as the only source of carbon atoms. (Assume that all other common reagents used in organic synthesis are available to be used in this synthesis.) For each step in the synthesis, identify the type of reaction that is occuring. b. Draw the two isomers of CaHfi. The values of All? for these isomers (in kJ/mol) are 20.42 and 53.30. Assign each isomer its value of AH? and briefly explain your assignment. ...
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CHM140Y5Y05 Exam - Name: _—__.._..______ Student Number:...

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