Multiple-choice Questions 1-21 Circle the appropriate response. (2 marks each) 1. The hydroxyl group occurs in a) phenols and ketones. b) alcohols only. c) ketones and carboxylic acids. d) aldehydes and alcohols. e) alcohols, phenols, and carboxylic acids. 2. Butane reacts with a) boiling aqueous sodium hydroxide. b) boiling nitric acid. c) concentrated sulfuric acid. d) chlorine when heated. e) the strong oxidizing agent KMn 4. 3. Which of the following is an unsaturated hydrocarbon? a) C 5 H 12 b) C 4 H 10 c) C 3 H 4 d) C 4 H 8 e) C 3 H 8 4. The compound (CH 3 ) 2 CHCH(CH 3 )CH 2 CH(CH 2 CH 3 )CH 2 CH 2 CH 3 is named as a) a decane. b) a heptane. c) a hexane. d) a nonane. e) an octane. 1
5. Consider the following reaction: 2NCl(g) 2N(g) + Cl 2 (g) The initial concentration of NCl(g) is 2.5 M. If [Cl 2 ] = 0.60 M at equilibrium, calculate the equilibrium concentration of NCl(g). a) 1.2 M b) 1.3 M c) 1.9 M d) 2.2 M e) 0.70 M 6. For the following reaction H 2 (g) + I 2 (g) 2HI(g) K c = 54 at 700 K. At equilibrium the concentration of H 2 is 0.021 M and of I 2 is 0.013 M. Calculate the equilibrium concentration of HI. a) 0.80 M b) 0.017 M c) 0.015 M d) 0.12 M e) 0.0020 M 7. Consider the following reaction: P 4 (g) + 5 2 (g) P 4 10 (s) If the initial concentration of 2 (g) is 1.0 M, and "x" is the equilibrium concentration of 2 (g), what is the correct equilibrium relation? a) K c = 5x 6 b) K c = 5/x 6 c) K c = x 6 d) K c = 1/x 6 e) K c = 1/x 5 2
8. Consider the following reaction: NH 4 (NH 2 C 2 )(s) 2NH 3 (g) + C 2 (g) If the initial concentration of NH 3 (g) is 1.0 M, and "x" is the equilibrium concentration of NH 3 (g), what is the correct equilibrium relation? (The solid is in excess.) a) K c = (1.0 x) 2 (x/2) b) K c = x 3 c) K c = x 3 /2 d) K c = (1.0 x) 2 (x) e) K c = 4x 3 9. Which of the following 0.10 M aqueous solutions gives the lowest ph? a) CH 3 CH (pk a = 4.75) b) H 3 P 4 (pk a1 = 2.12) c) HI 3 (pk a = 0.77) d) HF (pk a = 3.45) e) Since all are acids, the ph is the same for all solutions. 10. When Ca(s) is dissolved in water which of the following is true? a) The solution contains H (aq) and Ca 2+ (aq). b) The solution contains 2 (aq) and Ca 2+ (aq). c) The solution contains 2 (aq), H (aq), and Ca 2+ (aq). d) The solution contains Ca(aq). e) Ca(s) does not dissolve in water. 11. What is the ph of 0.010 M HCN(aq) (K a = 4.9 10 10 )? a) 5.65 b) 4.65 c) 9.31 d) 2.00 e) 6.69 3
12. When 500 ml of 0.120 M KH(aq) is mixed with 500 ml of 0.0480 M Ba(H) 2 (aq), the ph of the resulting solution is a) 13.03 b) 14.00 c) 13.23 d) 12.92 e) 13.33 13. Which one of the following gives a neutral aqueous solution? a) Cu(Cl 4 ) 2 b) LiCl 4 c) NaN 2 d) KF e) C 5 H 5 NH(Cl 4 ) 14. What is the ph of an aqueous solution that is 0.10 M HCH (K a =1.8 10 4 ) and 0.10 M NaHC 2? a) 3.74 b) 10.26 c) 5.62 d) 2.38 e) 5.74 15. Which of the following indicators would be most suitable for the titration of 0.10 M HBr(aq) with 0.10 M KH(aq)? a) bromothymol blue (pk In = 7.1) b) thymol blue (pk In = 1.7) c) bromophenol blue (pk In = 3.9) d) alizarin yellow (pk In = 11.2) e) methyl orange (pk In = 3.4) 4
16. Which one of the following salts gives an acidic aqueous solution? a) NH 4 F b) NH 4 CN c) (NH 4 ) 2 S d) (NH 4 ) 3 P 4 e) (NH 4 ) 2 C 3 17. All of the following changes give a positive ΔS r o except a) H 2 (s) H 2 (l) b) H 2 (l, 20 o C) H 2 (l, 50 o C) c) N 2 (g) + 3H 2 (g) 2NH 3 (g) d) H 2 (l) H 2 (g) e) Na(l) Na(g) 18. Which of the following conditions will result in a spontaneous reaction at all temperatures? a) ΔH < 0, ΔS < 0 b) ΔH > 0, ΔS < 0 c) ΔH < 0, ΔS > 0 d) ΔH > 0, ΔS > 0 e) ΔH > 0, ΔS = 0 19. The equilibrium constant for the reaction Hg(l) Hg(g) is 3.6 10 4 at 100 o C. Calculate ΔG r o for this reaction. a) 24.6 kj b) 24.6 kj c) 0 d) 6.59 kj e) 6.59 kj 5
20. Consider the following reaction at 298 K. HCl(aq) + H 2 (l) Cl (aq) + H 3 + (aq) K c = 3.0 10 8 Calculate ΔG r when [Cl ] = [H 3 + ] = 1.0 10 6 M and [HCl] = 0.10 M. a) 62.6 kj b) 23.0 kj c) 19.8 kj d) 42.8 kj e) 42.8 kj 21. Which of the following reactions has the largest positive molar entropy change? a) N 2 (g) + 3H 2 (g) 2NH 3 (g) b) KCl 4 (s) + 4C(s) KCl(s) + 4C(g) c) CH 4 (g) + 2 2 (g) C 2 (g) + 2H 2 (g) d) PCl 5 (g) PCl 3 (g) + Cl 2 (g) e) H 2 (s) H 2 (g) Short-answer Questions 22-25 (4 marks each) 22. Write an equation for the synthesis of (a) CH 3 CH 2 CH 2 C(=)CH 3 (b) 2-butanone (c) CH 3 CH 2 C(=)NHCH 3 6
23. Calculate the ph of 0.0010 M H 2 S 4 (aq) (K a for HS 4 is 0.012). 24. How much MgCl 2 must be added to 1.0 L of water at ph = 8.9 to start precipitation of Mg(H) 2? 7
25. Consider the following reaction: 2S 3 (g) 2S 2 (g) + 2 (g) For an initial concentration of S 3 (g) equal to 0.0264 M, at equilibrium it is found that the concentration of 2 (g) equals 0.00280 M. Calculate the concentrations of S 3 (g) and S 2 (g) at equilibrium. 8
Long-answer Questions (6 marks each) 26. In each case, circle and identify all the functional groups. a) Cortisone - anti-inflamatory drug used in the treatment of rheumatoid arthritis. H 3 C H H CH 3 H H b) Vanillin - the principal component responsible for the characteristic taste of vanilla. H H CH 3 9
27. Consider water evaporating. a. Using the data sheet calculate the ΔG o of this physical change and state whether it is spontaneous. b. Calculate the ΔS o of this change of state. Does entropy increase or decrease? c. Finally, at what temperature (from calculated ΔH o and ΔS o values) would this reaction be spontaneous? Is this a reasonable approximation? 10
28. A sealed 10.0 L container is charged with 0.25 g of hydrogen and 25.1 g of iodine at 124 o C. a) What is the initial pressure of this vessel (before reaction)? b) Given that the hydrogen and iodine react and are in equilibrium with hydrogen iodide according to the equation below; what will the total pressure be at equilibrium? H 2 (g) + I 2 (g) 2HI (g) **** END F EXAM **** 11
Answer Key 1. e 2. d 3. d 4. e 5. b 6. d 7. b 8. c 9. c 10. a 11. a 12. a 13. b 14. a 15. a 16. a 17. d 18. c 19. b 20. c 21. b 22. a. CH 3 CH 2 CH 2 C(=)H + HCH 3 b. CH 3 CH(H)CH 2 CH 3 + Na 2 Cr 2 7 / H 2 S 4 c. CH 3 CH 2 C(=)H + H 2 NCH 3 23. 0.0010 M H 2 S 4 ===> HS 4 - ph = 3 HS 4 - Η + + S 4 -.001 - x x x K a = 0.012 = x 2 /(0.001 - x) From quadratic x = [H + ] = 9.28 x 10-4 M Contributions from both K a1 and Ka2 [H + ] = 9.28 x 10-4 + 0.001 ===> ph = 2.7 24. ph = 8.9 ===> [H - ] = 7.94 x 10-6 K sp = [Mg 2+ ][H - ] 2 1 x 10-11 = [Mg 2+ ][7.94 x 10-6 ] 2 12
[Mg 2+ ] = 1.58 x 10-1 M or 1.58 x 10-1 moles in the 1.0 L Mass = (1.58 x 10-1 mol)(95.21 g/mol) = 15.1 g 25. 2S 3 <===> 2S 2 + 2 0.0264-2x 2x x [ 2 ] = x = 0.00280 [S 2 ] = 2x = 5.6 x 10-3 M [S 3 ] = 0.0264-2x = 2.08 x 10-2 M 26. H 3 C H H H CH 3 H H H CH 3 27. a) ΔG o = ΣΔG o f (Products) - ΣΔG o f (Reactants) = (-228.6) - (-236.8) = 8.2 kj/mol not spontaneous! b) ΔG = ΔH - TΔS 8.2 = 44.1 -(298) ΔS o ΔS o = 120.5 J/molK increased entropy c) ΔH = TΔS 44.1 = T(0.1205) T = 366K or 93 o C Yes, roughly expected boiling point. 28. a) H 2 = (0.25 g)/(2.016 g/mol) = 1.24 x 10-1 mol I 2 = (25.1 g)/(253.8 g/mol) = 9.889 x 10-2 mol P = nrt/v = (2.23 x 10-1 mol)(0.0821)(397 K)/(10.0 L) P = 7.26 x 10-1 atm b) The same as part (a). Note total pressure is always the same in this case, because of equal moles of gas on each side of the equation. 13