CHEM 1412 Practice Exam 3, Chapters 18, 19 & 24 Chang F = 96485 J/V mol = 96485 C/mol of e Ecell = E cell (0.0592/n) log(q) = E cell (0.0257/n) ln(q) G = n F E cell G = RT ln(keq) lnnt = kt + lnno Amp = C/sec R = 8.314 J/(mol K) c = 2.998 X 10 8 m/s mass of proton = 1.007276470 amu mass of neutron = 1.008664904 amu A periodic table is also attached. 1. The gain of electrons in a reaction is called a) reduction b) oxidation 2. What is the oxidation state of P in the phosphate ion, PO4 3? a) +2 b) +3 c) +5 d) +6 3. What substance is oxidized in the following reaction? Cr2O7 2 + 3 SO3 2 + 8 H + 2 Cr 3+ + 3 SO4 2 + 4 H2O a) Cr2O7 2 b) SO3 2 c) H + d) SO4 2 4. What is the coefficient of water when the following equation is balanced in acidic aqueous solution? Cr2O7 2 + Br Cr 3+ + Br2 a) 5 b) 6 c) 7 d) 8
5. The electrode at which oxidation occurs is called the a) anode b) cathode c) salt bridge 6. The half-reaction occurring at the cathode in the voltaic cell reaction 3 - MnO4 (aq) + 24 H + (aq) + 5 Fe (s) 3 Mn 2+ (aq) + 5 Fe 3+ (aq) + 12 H2O (l) is a) MnO4 (aq) + 8H + (aq) + 5e Mn 2+ (aq) + 4 H2O (l) b) Fe (s) Fe 3 + (aq) + 3 e c) Fe (s) Fe 2+ (aq) + 2 e d) Fe 2+ (aq) Fe 3+ (aq) + e 7. Given the following standard reduction potentials: Pb 2+ (aq) + 2 e Pb(s) E = 0.126 V Cu 2+ (aq) + 2 e Cu(s) E = +0.337 V calculate E cell for a voltaic cell based on these half-reactions. a) 0.463 V b) 0.211 V c) 1.95 V d) -0.211 V 8. E o cell for the following reaction is +0.13 V. What is the value of G (in kj) for the reaction? Pb (s) + 2 H + (aq) H2 (g) + Pb 2+ (aq) a) 25 kj b) 15 kj c) 52 kj d) 62 kj 9. The reaction O2 (g) + 4 H + (aq) + 4 Fe 2+ (aq) 4 Fe 3+ (aq) + 2 H2O (l) has E = +0.46 V. What is the value of the equilibrium constant for this reaction? a) 1.05 X 10 9 b) 2.67 X 10 18 c) 4.64 X 10-22 d) 1.27 X 10 31
10. One of the differences between a voltaic cell and an electrolytic cell is that in a voltaic cell a) an electric current is produced by a chemical reaction. b) electrons flow toward the anode. c) a nonspontaneous reaction is forced to occur using an electric current from an external source. d) reduction occurs at the anode. 11. If the value of Ecell for the following reaction is +0.95 V at 25 C, what is the concentration of Cu 2+ ion if the concentration of Zn 2+ is 1.0 M? Zn (s) + Cu 2+ (aq) Cu (s) + Zn 2+ (aq) E cell = +1.10 V a) 1.5 X 10 5 M b) 8.6 X 10 6 M c) 4.4 X 10 5 M d) 2.7 X 10 4 M 12. How many grams of copper metal can be obtained by passing a current of 1.50 amp through a solution of Cu 2+ (aq) for 45 minutes? (Show calculation) 13. Write the nuclear equation for the beta decay of iodine-131. 14. By what process does oxygen-15 decay to nitrogen-15? a) positron emission b) alpha emission c) beta emission d) gamma emission 15. The alpha decay of what isotope of what element produces lead-206? a) polonium-210 b) thallium-204 c) radon-222 d) bismuth-208
16. Radioactive carbon-14 is produced in the upper atmosphere by the reaction 14 7N + X > 14 6C + 1 1H What is the particle X? a) alpha b) beta c) proton d) neutron 17. Carbon-13 is stable, carbon-14 is radioactive. What type of radioactive decay is carbon-14 expected to undergo? a) alpha b) beta c) positron d) electron capture 18. In the nuclear transmutation, 16 8O (p, ) X, what is the product nucleus X? a) oxygen-16 b) oxygen15 c) nitrogen-13 d) nitrogen-14 19. What order process is radioactive decay? a) zero order b) first order c) second order d) third order 20. An ancient wooden artifact is believed to be 5000 years old. What percentage of the carbon-14 originally in the artifact would remain after this time? The half-life of carbon-14 is 5730 years. (Show calculation) 21. Carbon-11 has a half-life of 20.4 minutes. Assuming you start with a 500 g sample of carbon-11, how much will remain after 24 hours? (Show calculation) 22. The mass of the iron-56 nucleus is 55.92066 amu. What is the mass defect of this nucleus? (Show calculation)
23. The mass defect of the helium-4 nucleus is 0.0304 amu. What is the nuclear binding energy of this nucleus in J? a) 1.56 X 10 11 b) 4.95 X 10 10 c) 4.54 X 10 12 d) 1.92 X 10 9 24. In a nuclear power plant, a) a subcritical mass of uranium-235 is used. b) enough uranium-235 is used to maintain a chain reaction. c) small nuclei are fused together to form a larger nucleus. d) slow moving protons cause the fission of uranium-235. 25. The general formula of a cyclic alkene is a) CnH2n+2 b) CnH2n c) CnH2n-2 d) CnHn 26. Which is incorrect? a) ethane, C2H6 b) propane, C3H8 c) butane, C4H10 d) pentane, C5H10 27. Which is the carboxylic acid functional group? O O O O a) C H b) C OH c) C d) C NH2 28. Name the following compound: CHCH2CH2CHCH2CHCH2 CH2 a) 5,7-diethyl-2-methyloctane b) 4-ethyl-1,1,6-trimethyloctane c) 5-ethyl-2,7-dimethylnonane d) 5-ethyl-3,8-dimethylnonane 29. Draw the following molecule: trans-5-methyl-2-hexene 30. Draw the following molecule: 1-ethyl-1-methylcyclopentane
31. Which is the isopropyl group? a) CH2CH2 b) CH c) CH2 d) CH2CH2CH 32. Structural isomers have a) the same structure but different molecular formulas. b) their atoms connected in the same order. c) their atoms connected in a different order. d) different structures and different molecular formulas. 33. Draw and name the structural isomers which have the molecular formula C4H9Br.
Answers 1. A 12. 23. C 2. C 13. 24. B 3. B 14. A 25. C 4. C 15. A 26. D 5. A 16. D 27. B 6. A 17. B 28. C 7. A 18. C 29. 8. A 19. B 30. 9. D 20. 31. B 10. A 21. 32. C 11. B 22. 33. 4. Cr2O7 2 (aq) + 6 Br (aq) + 14 H + (aq) 2 Cr 3+ (aq) + 3 Br2 (aq) + 7 H2O (l) 7. Oxidation Half-Reaction: Pb (s) Pb 2+ (aq) + 2 e E = 0.126 V Reduction Half-Reaction: Cu 2+ (aq) + 2 e Cu (s) E = +0.337 V _ Overall: Pb (s) + Cu 2+ (aq) Cu (s) + Pb 2+ (aq) E cell = +0.463 V 8. ΔG = (2)(96485 J mol 1 K 1 )(+0.13 V) = 25086 J 25 kj 9. ΔG = (4)(96485 J mol 1 K 1 )(+0.46 V) = 177532.4 J 177532.4 J = (8.314 J mol 1 K 1 )(298.15 K)ln(Keq), Keq = e 71.61975 = 1.27 X 10 31 12. (1.5 C/s)(45 min)(60 s/min) = 4050 C (4050 C)(1 mol e / 96485 C)(1 mol Cu / 2 mol e )(63.546 g Cu / mol Cu) = 1.3 g of Cu 13. 131 53I 0 1e + 131 54Xe 14. 15 8O 15 7N + 0 +1e (positron emission) 15. X 4 2He + 206 82Pb X = 210 84Po (polonium-210) 16. X = 1 0n (neutron) 17. Carbon-14 has too many neutrons (n/p ratio is too high for stability); -decay reduces the n/p ratio. 18. 16 8O + 1 1H 4 2He + X X = 13 7N (nitrogen-13) 20. k = ln(2) / t½ = 1.2097 X 10 4 yr 1 N0 = 100% Nt =? ln(nt) = (1.2097 X 10 4 yr 1 )(5000 yr) + ln(100%) Nt = 54.6% 54.6% of the original amount of carbon-14 remains. 21. k = ln(2) / t½ = ln(2) / 29.4 min = 0.033978 min 1, t = (24 hr)(60 min/hr) = 1440 min ln(nt) = kt + ln(no), ln(nt) = (0.033978 min 1 )(1440 min) + ln(500 g) ln(nt) = 42.7137, Nt = e 42.7137 = 2.82 X 10 19 g of carbon-11 remains
Another way to calculate Nt is, Nt = (½) n No where n = number of half-lives = t / t½ n = 1440 min / 20.4 min/half-life = 70.588 half-lives No = 500 g. Therefore, Nt = (½) 70.588 (500 g) = 2.82 X 10 19 g of carbon-11 remains. 22. Mass of 26 protons = (26 p)(1.007276470 amu/p) = 26.18918822 amu Mass of 30 neutrons = (30 n)(1.008664904 amu/n) = 30.25994712 amu 56.44913534 amu 55.92066 amu Mass defect = 0.52848 amu 23. ΔE = Δmc 2 = (0.0304 amu)(1 g / 6.022 X 10 23 amu)(1 kg / 1000 g)(2.998 X 10 8 m/s) 2 = 4.54 X 10 12 J 29. H \ / C==C / \ H CH2 CH trans-5-methyl-2-hexens 30. 1-ethyl-1-methylcyclopentane 33. CH2 CH2 CH2 Br 1-bromobutane CH2 CH Br 2-bromobutane CH CH2 Br 1-bromo-2-methyl-propane C Br 2-bromo-2-methylpropane