School of Chemistry and Physics Westville Campus, Durban BARCODE CHEMICAL REACTIVITY - CHEM120 TEST 2 Date: Tuesday, 8 October 2013 Total marks: 25 Time: 17h45 18h30 IMPORTANT: Complete this part immediately. Name: Student No: Tutorial Day: Tutorial Venue: Tutor s Name: INSTRUCTIONS: 1. Answer ALL questions. 2. For Section A which contains the multiple choice questions, write your answers on the multiple choice answer sheet and follow the instructions given in the question. 3. Calculators may be used but all working must be shown. 4. The pages of this test must not be unpinned. 5. Your answers for Section B must be written on the question paper in the spaces provided. The left-hand pages may be used for extra space or for rough work. 6. Marks will be deducted for the incorrect use of significant figures and the omission of units. 7. You must write legibly in black or blue ink. Pencils and Tipp-Ex are not allowed. 8. This test consists of 9 pages. Please check that you have them all. 9. A data sheets and a periodic table are provided. Question No. Section A 1 2 3 4 5 Mark 10 4 3 2 2 4 Total Mark 25 Final Percentage: /25 %
SECTION A - Multiple Choice Questions For each of the following questions, select the correct answer from the list provided. There is only one correct answer for each question. Indicate your answer on the multiple choice answer sheet provided. Make a dark heavy mark with HB pencil that fills the block of the appropriate letter completely. 1. Which of the following changes is not exothermic? (1) A. Combustion of butane. B. Freezing water. C. Condensing steam. D. Melting copper. 2. The specific heat capacity of water is 4.18 J K 1 g 1. What is the enthalpy change when 10.00 g of water is heated from 285.0 K to 300.0 K? (1) A. 2.79 J B. 627 kj C. 6.27 kj D. 627 J 3. The heats of formation (Δ f H o ) at 298 K for SO 2 (g) and SO 3 (g) are 296.8 and 395.7 k J mol 1 respectively. What is the enthalpy (Δ r H o ) at 298 K per mole of SO 2 for the reaction: 2SO 2 (g) + O 2 (g) 2SO 3 (g) (2) A + 98.9 kj mol 1 B 692.5 kj mol 1 C 197.8 kj mol 1 D 98.9 kj mol 1 2
4. Which statement is incorrect about entropy? (1) A. A pure, perfect crystal has zero entropy at 0 K. B. For a phase change, ΔS = 0. C. The entropy of a system + surroundings increases during a spontaneous, irreversible process. D. The value of S o for a compound or element depends on temperature. 5. Which one of the following is a valid expression for the rate of the reaction below? 4NH3 + 7O2 4NO2 + 6H2O (1) A. B. C. D. 6. Which transformation could take place at the anode of an electrochemical cell? (2) A. NO NO 3 - B. CO 2 Cr 2 O 4 2- C. VO 2 + VO 2+ D. H 2 AsO 4 H 3 AsO 3 3
7.Which one of the following graphs shows the correct relationship between concentration and time for a reaction that is second order in [A]? (1) A. B. C. D. 8. The standard cell potential (E cell ) for the voltaic cell based on the reaction below is V. (1) Sn 2+ (aq) + 2Fe 3+ (aq) 2Fe 2+ (aq) + Sn 4+ (aq) A. +0.46 B. +0.617 C. +1.39 D. -0.46 End of Section A 4
SECTION B QUESTION 1 (4) A mass of 100.0 g of water was placed in a constant-pressure calorimeter. The temperature of the water was recorded as 295.0 K. A copper block of mass 20.0 g was heated to 353.0 K and then dropped into the water in the calorimeter. What was the final temperature of the water if the specific heat capacities of water and copper are 4.18 and 0.385 J K 1 g 1, respectively? Solution 5
QUESTION 2 (3) Calculate the ΔH for the reaction ½ H 2 (g) + ½ Cl 2 (g) HCl (g) Given that: ΔH = 47.5 kj ΔH = 105 kj ΔH = -402.5 kj Solution ΔH = 47.5 kj..i ΔH = 105 kj...ii ΔH = -402.5 kj iii To get ½ H 2 (g) + ½ Cl 2 (g) HCl (g) Reverse eqn ii, add eqns i and iii ΔH = -105 kj...ii [ H = - 105 +47.5 + -402.5 = - 460 kj]1/2 H = -230 kj 6
QUESTION 3 (3) The reaction of iodide ions with hypochlorite ions, OCl- (the active ingrediant in a chlorine bleach such as Jik), follows the equation OCl - + I - OI - + Cl -. It is a rapid reaction that gives the following rate data: Initial Concentration / mol dm -3 Rate of formation of Cl - / mol dm -3 s -1 [OCl - ] [I - ] 1.7 x 10-3 1.7 x 10-3 1.75 x 10 4 3.4 x 10-3 1.7 x 10-3 3.50 x 10 4 1.7 x 10-3 3.4 x 10-3 3.50 x 10 4 What is the rate law for the reaction? SOLUTION: Rate = k [OCl - ] a [I - ] b ( ) 2 = 2 a a = 1 ( ) 2 = 2 b Rate = k [OCl - ] 1 [I - ] 1 a = 1 7
QUESTION 4 (2) A voltaic cell is constructed that uses the following reaction and operates at 298 K: Zn(s) + Ni 2+ (aq) Zn 2+ (aq) + Ni(s) The emf of this cell under standard conditions is +0.48 V. What is the emf of this cell when [Ni 2+ ] = 3.00 M and [Zn 2+ ] = 0.10 M? SOLUTION: Anode (oxidation): Zn(s) Zn 2+ (aq) + 2 e - Cathode (reduction): Ni 2+ (aq) + 2 e - Ni(s) R = 8.314 J mol -1 K -1 n = 2 [Ni 2+ ] = 3.00 M T = 298 K Eº cell = 0.48 V [Zn 2+ ] = 0.10 M F = 96485 J V -1 mol -1 lnq = 0.48 V - = 0.52 V QUESTION 5 (a) Draw the structural formula of (E)-1-amino-2-butene and indicate whether it is a primary (1 ), secondary (2 ), tertiary (3 ) or quaternary (4 ) amine. (2) NH 2 Primary (1 ) amine 8
(b) Give the IUPAC name for each of the following compounds: (2) (i) 3-ethyl-2,4-dimethylheptane (ii) O 3-methylpentan-2-one 9
STANDARD REDUCTION POTENTIALS IN VOLTS AT 25 C E F2(g) + 2e 2F - (aq) + 2.85 Co3+(aq) + e Co2+(aq) + 1.82 MnO4-(aq) + 8H+(aq) + 5e 4H2O + Mn2+(aq) + 1.52 ClO4-(aq) + 8H+(aq) + 8e 4H2O + Cl (aq) + 1.39 Cl2(g) + 2e 2Cl (aq) + 1.36 Cr2O7 2- (aq) + 14H+(aq) + 6e 7H2O + 2Cr3+(aq) + 1.33 MnO2(s) + 4H+(aq) + 2e 2H2O + Mn2+(aq) + 1.23 O2(g) + 4H+(aq) + 4e 2H2O(l) + 1.23 Br2(l) + 2e 2Br (aq) + 1.06 NO3 (aq) + 4H+(aq) + 3e 2H2O +NO(g) + 0.96 Hg2+(aq) + 2e Hg(l) + 0.85 Ag+(aq) + e Ag(s) + 0.80 Fe3+(aq) + e Fe2+(aq) + 0.77 MnO4 (aq) + 2H2O + 3e 4OH (aq) + MnO2(s) + 0.59 I2(s) + 2e 2I (aq) + 0.54 Cu2+(aq) + 2e Cu(s) + 0.34 Sn4+(aq) + 2e Sn2+(aq) + 0.15 2H+(aq) + 2e H2(g) 0.00 Pb2+(aq) + 2e Pb(s) 0.13 Sn2+(aq) + 2e Sn(s) 0.14 Ni2+(aq) + 2e Ni(s) 0.24 Cd2+(aq) + 2e Cd(s) 0.40 Fe2+(aq) + 2e Fe(s) 0.44 Zn2+(aq) + 2e Zn(s) 0.76 Mn2+(aq) + 2e Mn(s) 1.18 Al3+(aq) + 3e Al(s) 1.66 Mg2+(aq) + 2e Mg(s) 2.34 Na+(aq) + e Na(s) 2.71 Ca2+(aq) + 2e Ca(s) 2.87 Li+(aq) + e Li(s) 3.04 10
11 1 18 1 H 1.008 2 13 14 15 16 17 2 He 4.003 3 Li 6.941 4 Be 9.012 Periodic Table 5 B 10.81 6 C 12.01 7 N 14.01 8 O 16.00 9 F 19.00 10 Ne 20.18 11 Na 22.99 12 Mg 24.31 3 4 5 6 7 8 9 10 11 12 13 Al 26.98 14 Si 28.09 15 P 30.97 16 S 32.07 17 Cl 35.45 18 Ar 39.95 19 K 39.10 20 Ca 40.08 21 Sc 44.96 22 Ti 47.88 23 V 50.94 24 Cr 52.00 25 Mn 54.94 26 Fe 55.85 27 Co 58.93 28 Ni 58.69 29 Cu 63.55 30 Zn 65.39 31 Ga 69.72 32 Ge 72.61 33 As 74.92 34 Se 78.96 35 Br 79.90 36 Kr 83.80 37 Rb 85.47 38 Sr 87.62 39 Y 88.91 40 Zr 91.22 41 Nb 92.91 42 Mo 95.94 43 Tc 98.91 44 Ru 101.1 45 Rh 102.9 46 Pd 106.4 47 Ag 107.9 48 Cd 112.4 49 In 114.8 50 Sn 118.7 51 Sb 121.8 52 Te 127.6 53 I 126.9 54 Xe 131.3 55 Cs 132.9 56 Ba 137.3 57* La 138.9 72 Hf 178.5 73 Ta 180.9 74 W 183.8 75 Re 186.2 76 Os 190.2 77 Ir 192.2 78 Pt 195.1 79 Au 197.0 80 Hg 200.6 81 Tl 204.4 82 Pb 207.2 83 Bi 209.0 84 Po (209) 85 At (210) 86 Rn (222) 87 Fr (223) 88 Ra (226) 89* * Ac (227) 104 Db (261) 105 Jl (262) 106 Rf (263) 107 Bh (262) 108 Hn (?) 109 Mt (?) * Lanthanide Series 58 Ce 140. 1 59 Pr 140. 9 60 Nd 144. 2 61 Pm (147) 62 Sm 150. 4 63 Eu 152. 0 64 Gd 157. 2 65 Tb 158. 9 66 Dy 162. 5 67 Ho 164. 9 68 Er 167. 3 69 Tm 168. 9 70 Yb 173. 0 71 Lu 175. 0 ** Actinide Series 90 Th (232) 91 Pa (231) 92 U (238) 93 Np (237) 94 Pu (239) 95 Am (243) 96 Cm (247) 97 Bk (247) 98 Cf (252) 99 Es (252) 100 Fm (257) 101 Md (256) 102 No (259) 103 Lr (260)
DATA SHEET Physical Constants Boltzmann constant k = 1.381 x 10-23 J K -1 Planck constant h = 6.626 x 10-34 J s Elementary charge e = 1.602 x 10-19 C Speed of light in vacuum c = 2.998 x 10 8 m s -1 = 2.998 x 10 10 cm s -1 Avogadro constant L or N A = 6.022 x 10 23 mol -1 Gas constant R = kl = 8.315 J K -1 mol -1 Molar volume of an ideal gas o m = 8.315 L kpa K -1 mol -1 = 0.08206 L atm K -1 mol -1 V = 22.414 L mol -1 (at 1.000 atm and 273.2 K) V m = 24.789 L mol -1 (at 100.0 kpa and 298.2 K) Faraday constant F = el = 9.6485 x 10 4 C mol -1 Atomic mass unit (amu) u = 1.661 x 10-27 kg Rest mass of electron m e = 9.109 x 10-31 kg Rest mass of proton m p = 1.673 x 10-27 kg Rest mass of neutron m n = 1.675 x 10-27 kg Vacuum permittivity ε υ = 8.854 x 10-12 J -1 C 2 m - 1 Standard acceleration of free fall g = 9.807 m s - 2 Rydberg constant for the H atom R H = 109677 cm -1 Conversion Factors 1 micron (μ) = 10-6 m = 1 μm 1 Ångström (Å) = 1 x 10-10 m = 0.1 nm = 100 pm 1 L = 10-3 m 3 = 1 dm 3 1 atm = 1.013 x 10 5 N m -2 = 1.013 x 10 5 Pa = 760 mmhg = 760 Torr 1 bar = 1.000 x 10 5 Pa 1 J = 0.2390 cal = 1 Pa m 3 = 1 m 2 kg s -2 1 cal = 4.184 J 1 ev = 1.602 x 10-19 J 1 L atm = 101.3 J 1 W = 1 J s -1 1 ppm = 1 μg g -1 = mg kg -1 = 1 mg L -1 (dilute aqueous solutions only) 1 tonne = 1000 kg Prefixes to Units P T G M k d c m μ n p f peta tera giga mega kilo deci centi milli micro nano pico femto 10 15 10 12 10 9 10 6 10 3 10-1 10-2 10-3 10-6 10-9 10-12 10-15 12