Name: Lab Day and Time: Instructions 1. Do not open the exam until you are told to start. 2. This exam is closed note and closed book. You are not allowed to use any outside material while taking this exam. 3. Use the spaces provided to write down your answers. To receive full credit, you must show all work. Do not write answers on any other pieces of paper. If you need more room, write on the back of the exam and be sure to include a note describing where the work is located. 4. When solving numerical problems, make sure you include the proper units in your final answer. 5. If a question asks for a response in sentence or paragraph form, make sure you respond in that format. 6. Useful data for the exam and a periodic table are provided on the last page of the exam. Carefully tear out these sheets if you wish. Page # Points possible Points awarded Page # Points possible Points awarded MC 9 5 20 3 27 6 9 4 16 7 18 8 4 Total 100 1
Multiple Choice Unless otherwise directed, choose the single best answer for each question. Please use the space provided to do your calculations. Make sure your answers have the proper number of significant figures. 1. Use the given information to calculate the equilibrium constant for the reaction below. H 2 CO 3 (aq) + 2NH 3 (aq) 2NH 4 + (aq) + CO 3 2- (aq) K =? Given H 2 CO 3 (aq) + 2H 2 O(l) 2H 3 O + (aq) + CO 2-3 (aq) K = 2.1x10-17 NH + 4 (aq) + H 2 O(l) H 3 O + (aq) + NH 3 (aq) K = 5.6x10-10 a.) 1.2x10-26 b.) 3.8x10-8 c.) 2.7x10 7 d.) 6.7x10 1 e.) None of the above. 2. The reaction shown below occurs at 25. At the beginning of the reaction the [N 2 ] = 0.100 M, the [H 2 ] = 0.200 M, and the [NH 3 ] = 0.0100 M. As the reaction progresses towards equilibrium, which way does the reaction shift and what happens to the equilibrium constant? 2NH 3 (g) N 2 (g) + 3H 2 (g) K = 16.6 a.) The reaction will shift right and K increases. b.) The reaction will shift left and K decreases. c.) The reaction will shift right and K remains constant. d.) The reaction will shift left and K remains constant e.) The reaction will shift left and K increases. 3. Which of the following would you expect to be the most acidic? a.) AgClO 4 (aq) b.) Be(ClO 4 ) 2 (aq) c.) NaClO 4 (aq) d.) Ti(ClO 4 ) 3 (aq) e.) None of the above is acidic. 2
4. a.) Next to the soluble ionic compounds listed below, indicate whether they will produce an acidic, basic, or neutral solution in water. If the compound is acidic or basic, also write a balanced chemical equation showing how the compound reacts in water on the line provided. If it is acidic or basic, calculate or write the Ka or Kb of the compound in the space just below the formula. (10 points) LiHSO 4 KCN b.) If 0.100 moles of each compound were added to a separate beaker of deionized water, which solution would have the biggest change in ph? (3 points) 5. A sample of Co(OH) 2 (s) is added to a container of deionized water and allowed to reach equilibrium. Co(OH) 2 (s) Co 2+ (aq) + 2OH - (aq) H > 0 a.) If this system is initially at equilibrium, in what direction will it shift in each of the following cases? (9 points) i.) Co 2+ is removed. ii.) NaOH(aq) is added. iii.) The temperature is increased. b.) The mass of Co(OH) 2 at equilibrium is 25.00 g. When KCl(aq) is added to the equilibrium mixture, the magnitude of the equilibrium constant doesn t change but the mass of Co(OH) 2 at equilibrium drops to 24.95 g. Explain why the mass drops. (5 points) 3
6. The following mechanism has been proposed for the reaction between nitric oxide and bromine. Step 1 NO(g) + Br 2 (g) NOBr 2 (g) slow Step 2 NOBr 2 (g) + NO NOBr(g) + NOBr(g) fast In the space below, draw the reaction profile for the mechanism. The overall reaction is exothermic. Identify the intermediate(s) and place them where they should appear, label any transition state(s) (as T.S.), and use an arrow to identify the magnitude of the activation energy for the overall reaction. (9 points) 7. How would the addition of a catalyst change the diagram above? (3 points) 8. At elevated temperatures, dinitrogen pentoxide decomposes to nitrogen dioxide and oxygen. 2N 2 O 5 (g) 4NO 2 (g) + O 2 (g) When the rate of formation of NO 2 is 3.8x10-4 M/s, what is the rate of change in the N 2 O 5 concentration? (4 points) 4
The next problem continues on the following page. 9. A solution containing HBr(aq) has a ph equal to 5.70. a.) What is the poh? (3 points) b.) What is the [H 3 O + ] in this solution? (4 points) c.) A solid sample of bromoacetic acid (CH 2 BrCOOH) is dissolved in 1.00 L of the above solution. If the sample contained 0.60 moles of bromoacetic acid, construct the ICE table that would allow you to calculate the ph of the mixture of HBr and bromoacetic acid. Assume the volume of the solution does not change. For simplicity, represent bromoacetic acid as HA. You do not need to solve anything, just set up the ICE table. (7 points) d.) Using the information from the ICE table, substitute the appropriate terms into the equilibrium constant expression. You do not need to solve the equation, just plug in the appropriate terms. (3 points) e.) What is the H 3 O + concentration of a neutral solution at a temperature of 25? (3 points) 5
f.) Use the information from the previous page to answer this question. What is the ph of the mixture of HBr and bromoacetic acid. You will have to make some assumptions to solve this problem. Clearly state your assumptions and check your assumptions when you are finished. Do not use the quadratic equation to solve this problem. (5 points) 10. The reaction shown below is an elementary reaction. Other than the presence of a catalyst, list as many things as you can think of that will affect the rate of the reaction. You do not need to write a sentence, just make a list. (4 points) NO 3 (g) + CO(g) NO 2 (g) + CO 2 (g) 6
11. The balanced chemical equation for the decomposition of A is: 3A(g) 2B(g) + C(g) a.) The concentration of A was monitored as a function of time. When 1/[A] was plotted as a function of time the relationship was linear and is shown to the right. What is the rate law for this reaction and what are the units of k? (5 points) b.) If the initial concentration of A is 1.00 mol/l, how long will it take for 85% of A to go away? (8 points) c.) The following mechanism has been proposed for the reaction above. Based on the rate law from part a, which step must be the slow step? In order to get full credit, you must show how the mechanism gives you the experimentally derived rate law. (5 points) Step 1 Step 2 Step 3 A D D + A 3B A + B C 7
12. The Lewis structures and Ka values for HNO 2 and HNO 3 are shown below. Ka = 7.2x10-4 Ka = 2.4x10 1 It has been suggested that the strength of an acid is primarily dependent on the properties of its conjugate base. Use Lewis structures and words to explain what it is about the conjugate bases of HNO 2 and HNO 3 that accounts for the difference in acid strength. (4 points) 8
Periodic Table and Other Useful Information Avogadro s Number: 6.022 x 10 23 particles/mole Formula Ka Dalton s Law: P A = χ A x P tot H 2 SO 4 1.0x10 3 - HSO 4 1.1x10-2 Integrated Rate Laws: [A] t = -kt + [A] 0 HCN 6.2x10-10 CH 2 BrCOOH 1.3x10-3 ln[a] t = -kt + ln[a] 0 Temperature conversion: Ideal Gas Law: Arrhenius Equation: 1 = kt + 1 [A] t [A] 0 T [K] = 273.15 + T [ C] PV = nrt k = Ae Ea RT Kw 1.0x10-14 The common strong bases are the soluble ionic compounds with OH -. The following will form soluble ionic compounds with OH - : Group I metals, calcium, strontium, and barium -1 Gas constant R: 8.314 J mol -1 K 0.08206 L atm K 1 mol 1 1 atmosphere: 760 torr (unlimited s.f.) 1 H 1.0079 3 Li 6.941 11 Na 22.9898 19 K 39.0983 37 Rb 85.4678 55 Cs 132.905 87 Fr (223) 4 Be 9.0122 12 Mg 24.3050 20 Ca 40.078 38 Sr 87.62 56 Ba 137.327 88 Ra 226.025 21 Sc 44.9559 39 Y 88.9059 57 La 138.906 89 Ac 227.028 22 Ti 47.88 40 Zr 91.224 72 Hf 178.49 104 Rf (261) 23 V 50.9415 41 Nb 92.9064 73 Ta 108.948 105 Db (262) 24 Cr 51.9961 42 Mo 95.94 74 W 183.85 106 Sg (263) 25 Mn 54.9380 43 Tc (98) 75 Re 186.207 107 Bh (262) 26 Fe 55.847 44 Ru 101.07 76 Os 190.2 108 Hs (265) 27 Co 58.9332 45 Rh 102.906 77 Ir 192.22 109 Mt (266) 28 Ni 58.693 46 Pd 106.42 78 Pt 195.08 110 Ds (269) 29 Cu 63.546 47 Ag 107.868 79 Au 196.967 111 Rg (272) 30 Zn 65.409 48 Cd 112.411 80 Hg 200.59 112 Cn (277) 5 B 10.811 13 Al 26.9815 31 Ga 69.723 49 In 114.82 81 Tl 204.383 113 Uut 6 C 12.011 14 Si 28.0855 32 Ge 72.61 50 Sn 118.710 82 Pb 207.2 114 Fl (289) 7 N 14.0067 15 P 30.9738 33 As 74.9216 51 Sb 121.757 83 Bi 208.980 115 Uup 8 O 15.9994 16 S 32.066 34 Se 78.96 52 Te 127.60 84 Po (209) 116 Lv (293) 9 F 18.9984 17 Cl 35.4527 35 Br 79.904 53 I 126.904 85 At (210) 117 Uus 2 He 4.0026 10 Ne 20.1797 18 Ar 39.948 36 Kr 83.80 54 Xe 131.29 86 Rn (222) 118 Uuo 58 Ce 140.12 90 Th 232.038 59 Pr 140.908 91 Pa 231.036 60 Nd 144.24 92 U 238.029 61 Pm (145) 93 Np (237) 62 Sm 150.36 94 Pu (244) 63 Eu 151.96 95 Am (243) 64 Gd 157.25 96 Cm (247) 65 Tb 158.925 97 Bk (247) 66 Dy 162.50 98 Cf (251) 67 Ho 164.930 99 Es (252) 68 Er 167.26 100 Fm (257) 69 Tm 168.934 101 Md (258) 70 Yb 173.04 102 No (259) 71 Lu 174.967 103 Lr (260) 9