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 2-5 36 6 21 7 19 8 21 In-Class EC 2.5 Attendance 3 Total 100 1
Multiple Choice Unless otherwise directed, choose the single best answer for each question. Some of the chemical equations will be balanced and some will not. Each question is worth three points. 1. Using the chemical equation below, calculate the number of moles of CuO that will be produced if 3.25 moles of O 2 react with excess Cu. Cu(s) + O 2 (g) CuO(s) a.) 3.25 mol CuO b.) 1.63 mol CuO c.) 9.75 mol CuO d.) 6.50 mol CuO When methane gas is combusted, it reacts with O 2 (g) and produces CO 2 (g) and H 2 O(g). The balanced chemical equation for this reaction is shown below. Use this equation and the diagrams below to answer the following three questions. CH 4 (g) + 2O 2 (g) CO 2 (g) + 2H 2 O(g) hydrogen oxygen carbon Before Reaction 2. Which compound is the excess reactant? After Reaction a.) CH 4 b.) O 2 c.) CO 2 d.) H 2 O 3. How many molecules were in the container before the reaction started? a.) 3 d). 7 b.) 5 c.) 6 4. If the size of the container remained the same and the pressure increased over the course of the reaction, which of the statements below could explain why the pressure increased. a.) The pressure increased because the number of gas particles decreased. b.) The pressure increased because the number of gas particles increased. c.) The pressure increased because the temperature decreased. d.) The pressure increased because the temperature increased. 2
5. A solution is made by dissolving 14.7 g of H 2 SO 4 in enough water to make 200.0 ml of solution. What is the molarity of this H 2 SO 4 solution? a.) 1.33 M b.) 0.749 M c.) 0.770 M d.) 0.0735 M 6. A small beaker containing deionized water and an unknown mass of Al(OH) 3 (s) is found in the laboratory. Realizing that Al(OH) 3 is a base you decide to titrate the solid with 0.9864 M HCl(aq). If the titration requires 51.86 ml of the HCl to reach the end point, what mass of Al(OH) 3 was in the beaker? M.M. of Al(OH) 3 = 78.0034 g / mole Al(OH) 3 a.) 1.995 g b.) 3.990 g c.) 1.330 g d.) 11.97 g 7. According to the balanced chemical equation shown below, if 13 g of C 2 H 2 are produced during a reaction, how many grams of H 2 O must have reacted? CaC 2 (s) + 2H 2 O(g) Ca(OH) 2 (s) + C 2 H 2 (g) Molar Mass (g/mole) 64.100 18.0153 74.093 26.038 a.) 4.5 g H 2 O b.) 9.0 g H 2 O c.) 4.8x10 2 g H 2 O d.) 18 g H 2 O 3
8. You have 100.0 ml of a 0.2500 M solution of NaCl sitting in a beaker. After several days you notice that water has evaporated and the volume has decreased. When you test the solution, you find that it is 0.3125 M NaCl. How much water must have evaporated? a.) 90.00 ml b.) 80.00 ml c.) 20.00 ml d.) 10.00 ml 9. When NH 3 is prepared from the reaction of 2.237 g of H 2 with excess N 2, the actual yield of NH 3 is 11.10 g. Calculate the percent yield. N 2 (g) + 3H 2 (g) 2NH 3 (g) Molar Mass (g/mole) 28.01348 2.01588 17.03056 a.) 6.667% b.) 88.10% c.) 20.15% d.) 82.00% 10. A 23.25 g sample of helium is held in a container. The pressure of helium inside the container is 635 mmhg and the temperature is 19.5 C. What is the volume of the container? a.) 668 L b.) 167 L c.) 11.1 L d.) 0.220 L 4
11. You need 0.234 moles of HCl for an experiment. What volume of 0.579 M HCl do you need to provide you with the proper amount of HCl? a.) 0.579 L b.) 2.47 L c.) 0.135 L d.) 0.404 L 12. Certain reactions will give off or release energy when they occur. This energy can be used in a number of ways, including powering vehicles, heating homes, and cooking. The reaction shown below releases 241.8 kj of energy. Since it releases energy, energy can be listed as a product in the balanced chemical equation and can be treated like any other product in stoichiometric calculations. 2H 2 (g) + O 2 (g) 2H 2 O(g) + 241.8 kj Molar Mass (g/mole) 2.01588 31.9988 18.0153 How much energy will be released when 0.453 g of H 2 reacts with excess O 2? (A kj is just a unit of energy) a.) 242 kj b.) 27.2 kj c.) 54.3 kj d.) 110. kj End of Multiple Choice 5
13. You are going to titrate a sample of HC 2 H 3 O 2 (aq) with a solution of NaOH(aq) just as you did in the second titration experiment in lab. a.) What have you done when you reach the equivalence point? (3 points) b.) What have you done when you reach the end point? (2 points) c.) When you do your calculations what do you assume? (3 points) 14. A sample of Co reacts with 22.50 ml of 0.1059 M HI to produce H 2 (g) as described in the balanced chemical equation below. The H 2 (g) is collected in a container over water at 17.00 C. The volume of the collected gas is 26.97 ml. Co(s) + 2HI(aq) CoI 2 (aq) + H 2 (g) a.) How many moles of H 2 gas are collected? (4 points) b.) What is the total pressure (in mmhg) inside the container holding the H 2 gas? (9 points) 6
15. A sample of 0.2561 M KOH is titrated with 0.9564 M H 2 SO 4. The balanced equation for the titration reaction is shown below. 2KOH(aq) + H 2 SO 4 (aq) 2H 2 O(l) + K 2 SO 4 (aq) a.) If the titration requires 35.68 ml of the H 2 SO 4 solution to reach the end point, what was the volume (in ml) of the sample of KOH? (8 points) b.) If 20.0 ml of 0.00300 M HCl was added to the sample of KOH before you started your titration, would the volume of H 2 SO 4 needed to reach the end point be larger, smaller, or no different than the value given above? (2 points) 16. In the table below, the name or formula for a chemical compound is given. Fill in the table with the corresponding name or formula of the chemical compound. (6 points) NAME FORMULA HBr lead(ii) oxalate Ba(NO 2 ) 2 17. Which of the two colors of light listed below is the least energetic? Circle your answer. (3 points) yellow light or blue light 7
18. Tetraphosphorus trisulfide, P 4 S 3, is used in the heads of wooden matches. This material can be manufactured by heating a mixture of red phosphorus and sulfur. The balanced chemical equation for this process is shown below. 8P 4 (s) + 3S 8 (s) 8P 4 S 3 (s) Molar Mass (g/mole) 123.8950 256.528 220.093 a.) If you start with 24.8 g of P 4 and 25.7 g of S 8, what mass of P 4 S 3 will you produce? You must use dimensional analysis and show all your work to receive full credit. (15 points) b.) What mass of each reactant will be left after the reaction is complete? (6 points) 8
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Conversion Factors, Constants, and Periodic Table Avogadro s Number: 6.022 x 10 23 particles/mole Pressure Conversion: 760 mmhg (torr) = 1 atm Ideal Gas Constant: L atm 0.08206 mol K Temperature conversion: T [K] = 273.15 + T [ C] Percent Yield: actual yield % yield 100% theoretical yield Vapor Pressure of Water at Various Temperatures Temperature ( C) Vapor Pressure (mmhg) 5.00 6.54 15.00 12.79 17.00 14.53 19.00 16.48 21.00 18.65 23.00 21.07 25.00 23.76 28.00 28.00 30.00 31.82 Dilution: M 1 V 1 =M 2 V 2 Gas Equations: P A P tot χ A PV nrt 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 Uun (269) 29 Cu 63.546 47 Ag 107.868 79 Au 196.967 111 Uuu (272) 30 Zn 65.409 48 Cd 112.411 80 Hg 200.59 112 Uub (277) 5 B 10.811 13 Al 26.9815 31 Ga 69.723 49 In 114.82 81 Tl 204.383 6 C 12.011 14 Si 28.0855 32 Ge 72.61 50 Sn 118.710 7 N 14.0067 15 P 30.9738 33 As 74.9216 51 Sb 121.757 8 O 15.9994 16 S 32.066 34 Se 78.96 52 Te 127.60 9 F 18.9984 17 Cl 35.4527 35 Br 79.904 53 I 126.904 2 He 4.0026 10 Ne 20.1797 18 Ar 39.948 36 Kr 83.80 54 Xe 131.29 82 83 84 85 86 Pb Bi Po At Rn 207.2 208.980 (209) (210) (222) 114 116 118 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) 11