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Unformatted text preview: AP Chemistry 2001 Free-Response Questions The materials included in these files are intended for use by AP teachers for course and exam preparation in the classroom; permission for any other use must be sought from the Advanced Placement Program. Teachers may reproduce them, in whole or in part, in limited quantities, for face-to-face teaching purposes but may not mass distribute the materials, electronically or otherwise. These materials and any copies made of them may not be resold, and the copyright notices must be retained as they appear here. This permission does not apply to any third-party copyrights contained herein. These materials were produced by Educational Testing Service (ETS), which develops and administers the examinations of the Advanced Placement Program for the College Board. The College Board and Educational Testing Service (ETS) are dedicated to the principle of equal opportunity, and their programs, services, and employment policies are guided by that principle. The College Board is a national nonprofit membership association dedicated to preparing, inspiring, and connecting students to college and opportunity. Founded in 1900, the association is composed of more than 3,900 schools, colleges, universities, and other educational organizations. Each year, the College Board serves over three million students and their parents, 22,000 high schools, and 3,500 colleges, through major programs and services in college admission, guidance, assessment, financial aid, enrollment, and teaching and learning. Among its best-known programs are the SAT®, the PSAT/NMSQT™, the Advanced Placement Program® (AP®), and Pacesetter®. The College Board is committed to the principles of equity and excellence, and that commitment is embodied in all of its programs, services, activities, and concerns. Copyright © 2001 by College Entrance Examination Board. All rights reserved. College Board, Advanced Placement Program, AP, and the acorn logo are registered trademarks of the College Entrance Examination Board. 22 8 9 26 27 28 29 30 2 Ba Cs *La 57 Hf 72 91.22 Zr 40 47.90 V Ta 73 92.91 Nb 41 50.94 Cr W 74 95.94 Mo 42 52.00 Mn Re 75 (98) Tc 43 54.938 †Actinide Series *Lanthanide Series Db (262) Rf †Ac 105 Pr 58 Ce Nd 60 (263) Sg 106 Pa Th U 92 Np 93 (145) Pm 61 (262) Bh 107 232.04 231.04 238.03 237.05 91 90 140.12 140.91 144.24 59 (261) 104 89 226.02 227.03 Ra Fr (223) 88 87 132.91 137.33 138.91 178.49 180.95 183.85 186.21 56 55 88.91 Y Sr 87.62 Rb 39 38 37 85.47 Sc 44.96 Ca 40.08 K 39.10 Ti (244) Pu 94 150.4 Sm 62 (265) Hs 108 190.2 Os 76 101.1 Ru 44 55.85 Fe Ni Pd 46 58.69 Cu Ag 47 63.55 Zn Cd 48 65.39 S 16 50 Sn 49 Ge 72.59 Ga 69.72 In Ar 18 36 52 Te Sb I 53 Xe 54 Br 79.90 Se 78.96 As 74.92 51 Kr 83.80 35 35.453 39.948 Cl 17 34 33 30.974 32 28.09 26.98 31 32.06 P 15 Si 14 Al 13 19.00 16.00 Au 79 Hg 80 Tl 81 Gd 64 (269) § 110 Tb 65 (272) § 111 Dy 66 (277) § 112 207.2 Pb 82 208.98 Bi 83 Ho 67 Er 68 Tm 69 §Not yet named 195.08 196.97 200.59 204.38 Pt 78 Yb 70 (209) Po 84 Lu 71 (210) At 85 (243) Am 95 (247) Cm 96 (247) Bk 97 (251) Cf 98 (252) Es 99 (257) Fm 100 (258) Md 101 (259) No 102 (260) Lr 103 151.97 157.25 158.93 162.50 164.93 167.26 168.93 173.04 174.97 Eu 63 (266) Mt 109 192.2 Ir 77 (222) Rn 86 102.91 106.42 107.87 112.41 114.82 118.71 121.75 127.60 126.91 131.29 Rh 45 58.93 Co 20 19 25 24.30 22.99 24 Mg Na 23 12 Ne 20.179 F 11 10.811 12.011 14.007 O 9.012 6.941 N Be Li C 10 B 4.0026 6 3 5 1.0079 He 21 7 2 4 PERIODIC TABLE OF THE ELEMENTS H 1 DO NOT DETACH FROM BOOK. INFORMATION IN THE TABLE BELOW AND IN THE TABLES ON PAGES 3-5 MAY BE USEFUL IN ANSWERING THE QUESTIONS IN THIS SECTION OF THE EXAMINATION. GO ON TO THE NEXT PAGE. STANDARD REDUCTION POTENTIALS IN AQUEOUS SOLUTION AT 25°C E °( V ) Half-reaction Li + + e - + eK + eRb + + e Ba 2 + + 2 e Sr 2 + + 2 e Ca 2 + + 2 e Na + + e Mg 2 + + 2 e Be 2 + + 2 e Al 3 + + 3 e Mn 2 + + 2 e Zn 2 + + 2 e Cr 3 + + 3 e Fe 2 + + 2 e Cr 3 + + e Cd 2 + + 2 e Tl + + e Co 2 + + 2 e Ni 2 + + 2 e Sn 2 + + 2 e Pb 2 + + 2 e 2 H + + 2 eS( s) + 2 H + + 2 e Sn 4 + + 2 e Cu 2 + + e Cu 2 + + 2 e Cu + + e I 2 ( s) + 2 e Fe 3 + + e Hg 2 2 + + 2 e Ag + + e Hg 2 + + 2 e 2 Hg 2 + + 2 e Br 2 (l ) + 2 e - “ “ “ “ “ “ “ “ “ “ “ “ “ “ “ “ “ “ “ “ “ “ “ “ “ “ “ “ “ “ “ “ “ “ “ Li( s) Cs( s) K ( s) Rb( s) Ba ( s) Sr( s) Ca ( s) Na ( s) Mg( s) Be( s) Al( s) Mn( s) Zn( s) Cr ( s) Fe( s) Cr 2 + Cd( s) Tl( s) Co( s) Ni( s) Sn( s) Pb( s) H 2 ( g) H 2S ( g) Sn 2 + Cu + Cu( s) Cu( s) 2 IFe 2 + 2 Hg(l ) Ag( s) Hg(l ) Hg 2 2 + 2 Br - -3.05 -2.92 -2.92 -2.92 -2.90 -2.89 -2.87 -2.71 -2.37 -1.70 -1.66 -118 . -0.76 -0.74 -0.44 -0.41 -0.40 -0.34 -0.28 -0.25 -0.14 -0.13 0.00 0.14 0.15 0.15 0.34 0.52 0.53 0.77 0.79 0.80 0.85 0.92 1.07 O 2 ( g) + 4 H + + 4 e Cl 2 ( g ) + 2 e Au 3 + + 3 e Co 3 + + e F2 ( g ) + 2 e - “ “ “ “ “ 2 H 2 O(l ) 2 Cl Au( s) Co 2 + 2 F- 1.23 1.36 1.50 1.82 2.87 Cs + + GO ON TO THE NEXT PAGE. 3 ADVANCED PLACEMENT CHEMISTRY EQUATIONS AND CONSTANTS ATOMIC STRUCTURE D E = hv c = lv = = = = u= n= m= E v l p h l = mu p = mu En = −2.178 × 10 −18 joule n2 EQUILIBRIUM Speed of light, c = 3.0 × 10 8 m s −1 Ka = [H + ] [A − ] [ HA ] Kb = [OH − ] [ HB + ] [ B] Planck’s constant, h = 6.63 × 10 −34 J s Boltzmann’s constant, k = 1.38 × 10 −23 J K −1 Avogadro’s number = 6.022 × 10 23 molecules mol −1 K w = [OH − ] [ H + ] = 1.0 × 10 −14 @ 25o C Electron charge, e = −1.602 × 10 −19 coulomb = Ka × K b pH = − log [ H + ], pOH = − log [OH − ] 14 = pH + pOH pH = pKa + log 1 electron volt per atom = 96.5 kJ mol −1 [A − ] [ HA ] Equilibrium Constants [HB + ] pOH = pKb + log [ B] pKa = − log Ka , pKb = − log Kb K p = Kc ( RT ) Dn energy frequency wavelength momentum velocity principal quantum number mass Ka Kb Kw Kp , where D n = moles product gas − moles reactant gas (weak acid) (weak base) (water) (gas pressure) Kc (molar concentrations) S o = standard entropy THERMOCHEMISTRY H o = standard enthalpy ∑ S o products −∑ S o reactants = ∑ DHfo products − ∑ DH fo reactants = ∑ DGfo products − ∑ DGfo reactants G o = standard free energy DS o = DH o DG o Eo T n m q c Cp DG o = DH o − TD S o = − RT ln K = −2.303 RT log K = −n Eo DG = DG o + RT ln Q = DG o + 2.303 RT log Q q = mcDT DH Cp = DT 1 faraday = = = = = = = standard reduction potential temperature moles mass heat specific heat capacity molar heat capacity at constant pressure = 96,500 coulombs GO ON TO THE NEXT PAGE. 4 GASES, LIQUIDS, AND SOLUTIONS PV = nRT  P + n a  (V - nb) = nRT  V 2 2 PA = Ptotal ™ X A , where X A = moles A total moles Ptotal = PA + PB + PC + . . . m n= M K = o C + 273 P1V1 PV = 22 T1 T2 m D= V 3kT 3 RT urms = = m M 1 KE per molecule = mu 2 2 3 KE per mole = RT 2 r1 M2 = r2 M1 = = = = = = u= P V T n D m pressure volume temperature number of moles density mass velocity urms KE r M p i Kf root-mean-square speed kinetic energy rate of effusion molar mass osmotic pressure van’t Hoff factor molal freezing-point depression constant Kb Q I q t molarity, M = moles solute per liter solution molality = moles solute per kilogram solvent DT f = iK f ™ molality = = = = = = = = = = = = molal boiling-point elevation constant reaction quotient current (amperes) charge (coulombs) time (seconds) E o = standard reduction potential K = equilibrium constant DTb = iKb ™ molality p = nRT i V Gas constant, R = 8.31 J mol −1 K −1 = 0.0821 L atm mol −1 K −1 = 8.31 volt coulomb mol −1 K −1 Boltzmann’s constant, k = 1.38 × 10 −23 J K −1 OXIDATION-REDUCTION; ELECTROCHEMISTRY K f for H 2 O = 1.86 K kg mol −1 Q= [C ] [ D ] c d a b Kb for H 2 O = 0.512 K kg mol −1 , where a A + b B → c C + d D [ A ] [ B] q I= t RT 0.0592 o o E cell = E cell − ln Q = E cell − log Q @ 25o C n n log K = STP = 0.000 o C and 1.000 atm Faraday’s constant, = 96,500 coulombs per mole of electrons nE o 0.0592 GO ON TO THE NEXT PAGE. 5 2001 AP® CHEMISTRY FREE-RESPONSE QUESTIONS CHEMISTRY Section II (Total time—90 minutes) Part A Time—40 minutes YOU MAY USE YOUR CALCULATOR FOR PART A. CLEARLY SHOW THE METHOD USED AND THE STEPS INVOLVED IN ARRIVING AT YOUR ANSWERS. It is to your advantage to do this, since you may obtain partial credit if you do and you will receive little or no credit if you do not. Attention should be paid to significant figures. Be sure to write all your answers to the questions on the lined pages following each question in the booklet with the pink cover. Do NOT write your answers on the green insert. Answer Question 1 below. The Section II score weighting for this question is 20 percent. 1. Answer the following questions relating to the solubility of the chlorides of silver and lead. (a) At 10°C, 8.9 ™ 10−5 g of AgCl(s) will dissolve in 100. mL of water. (i) Write the equation for the dissociation of AgCl(s) in water. (ii) Calculate the solubility, in mol L-1, of AgCl(s) in water at 10°C. (iii) Calculate the value of the solubility-product constant, Ksp, for AgCl(s) at 10°C. (b) At 25°C, the value of Ksp for PbCl2(s) is 1.6 ™ 10−5 and the value of Ksp for AgCl(s) is 1.8 ™ 10−10. (i) If 60.0 mL of 0.0400 M NaCl(aq) is added to 60.0 mL of 0.0300 M Pb(NO3)2(aq), will a precipitate form? Assume that volumes are additive. Show calculations to support your answer. (ii) Calculate the equilibrium value of [Pb2+(aq)] in 1.00 L of saturated PbCl2 solution to which 0.250 mole of NaCl(s) has been added. Assume that no volume change occurs. (iii) If 0.100 M NaCl(aq) is added slowly to a beaker containing both 0.120 M AgNO3(aq) and 0.150 M Pb(NO3)2(aq) at 25°C, which will precipitate first, AgCl(s) or PbCl2(s)? Show calculations to support your answer. Copyright © 2001 by College Entrance Examination Board. All rights reserved. Advanced Placement Program and AP are registered trademarks of the College Entrance Examination Board. GO ON TO THE NEXT PAGE. 6 2001 AP® CHEMISTRY FREE-RESPONSE QUESTIONS Answer EITHER Question 2 below OR Question 3 printed on page 8. Only one of these two questions will be graded. If you start both questions, be sure to cross out the question you do not want graded. The Section II score weighting for the question you choose is 20 percent. ∆H° = −114.1 kJ, ∆S° = −146.5 J K−1 2 NO(g) + O2(g) → 2 NO2(g) 2. The reaction represented above is one that contributes significantly to the formation of photochemical smog. (a) Calculate the quantity of heat released when 73.1 g of NO(g) is converted to NO2(g). (b) For the reaction at 25•C, the value of the standard free-energy change, DG•, is -70.4 kJ. (i) Calculate the value of the equilibrium constant, Keq , for the reaction at 25°C. (ii) Indicate whether the value of DG• would become more negative, less negative, or remain unchanged as the temperature is increased. Justify your answer. (c) Use the data in the table below to calculate the value of the standard molar entropy, S•, for O2(g) at 25•C. Standard Molar Entropy, S• (J K-1 mol-1) NO(g) 210.8 NO2(g) 240.1 (d) Use the data in the table below to calculate the bond energy, in kJ mol-1, of the nitrogen-oxygen bond in NO2 . Assume that the bonds in the NO2 molecule are equivalent (i.e., they have the same energy). Bond Energy (kJ mol-1) Nitrogen-oxygen bond in NO 607 Oxygen-oxygen bond in O2 495 Nitrogen-oxygen bond in NO2 ? Copyright © 2001 by College Entrance Examination Board. All rights reserved. Advanced Placement Program and AP are registered trademarks of the College Entrance Examination Board. GO ON TO THE NEXT PAGE. 7 2001 AP® CHEMISTRY FREE-RESPONSE QUESTIONS 3. Answer the following questions about acetylsalicylic acid, the active ingredient in aspirin. (a) The amount of acetylsalicylic acid in a single aspirin tablet is 325 mg, yet the tablet has a mass of 2.00 g. Calculate the mass percent of acetylsalicylic acid in the tablet. (b) The elements contained in acetylsalicylic acid are hydrogen, carbon, and oxygen. The combustion of 3.000 g of the pure compound yields 1.200 g of water and 3.72 L of dry carbon dioxide, measured at 750. mm Hg and 25°C. Calculate the mass, in g, of each element in the 3.000 g sample. (c) A student dissolved 1.625 g of pure acetylsalicylic acid in distilled water and titrated the resulting solution to the equivalence point using 88.43 mL of 0.102 M NaOH(aq). Assuming that acetylsalicylic acid has only one ionizable hydrogen, calculate the molar mass of the acid. (d) A 2.00 ™ 10-3 mole sample of pure acetylsalicylic acid was dissolved in 15.00 mL of water and then titrated with 0.100 M NaOH(aq). The equivalence point was reached after 20.00 mL of the NaOH solution had been added. Using the data from the titration, shown in the table below, determine (i) the value of the acid dissociation constant, Ka , for acetylsalicylic acid and (ii) the pH of the solution after a total volume of 25.00 mL of the NaOH solution had been added (assume that volumes are additive). Volume of 0.100 M NaOH Added (mL) pH 0.00 2.22 5.00 2.97 10.00 3.44 15.00 3.92 20.00 8.13 25.00 ? Copyright © 2001 by College Entrance Examination Board. All rights reserved. Advanced Placement Program and AP are registered trademarks of the College Entrance Examination Board. GO ON TO THE NEXT PAGE. 8 2001 AP® CHEMISTRY FREE-RESPONSE QUESTIONS CHEMISTRY Part B Time—50 minutes NO CALCULATORS MAY BE USED FOR PART B. Answer Question 4 below. The Section II score weighting for this question is 15 percent. 4. Write the formulas to show the reactants and the products for any FIVE of the laboratory situations described below. Answers to more than five choices will not be graded. In all cases, a reaction occurs. Assume that solutions are aqueous unless otherwise indicated. Represent substances in solution as ions if the substances are extensively ionized. Omit formulas for any ions or molecules that are unchanged by the reaction. You need not balance the equations. Example: A strip of magnesium is added to a solution of silver nitrate. (a) Sulfur dioxide gas is bubbled into distilled water. (b) A drop of potassium thiocyanate solution is added to a solution of iron(III) nitrate. (c) A piece of copper wire is placed in a solution of silver nitrate. (d) Solutions of potassium hydroxide and propanoic acid are mixed. (e) A solution of iron(II) chloride is added to an acidified solution of sodium dichromate. (f) Chlorine gas is bubbled through a solution of potassium bromide. (g) Solutions of strontium nitrate and sodium sulfate are mixed. (h) Powdered magnesium carbonate is heated strongly. Copyright © 2001 by College Entrance Examination Board. All rights reserved. Advanced Placement Program and AP are registered trademarks of the College Entrance Examination Board. GO ON TO THE NEXT PAGE. 9 2001 AP® CHEMISTRY FREE-RESPONSE QUESTIONS Your responses to the rest of the questions in this part of the examination will be graded on the basis of the accuracy and relevance of the information cited. Explanations should be clear and well organized. Examples and equations may be included in your responses where appropriate. Specific answers are preferable to broad, diffuse responses. Answer BOTH Question 5 below AND Question 6 printed on page 11. Both of these questions will be graded. The Section II score weighting for these questions is 30 percent (15 percent each). 5. Answer the questions below that relate to the five aqueous solutions at 25•C shown above. (a) Which solution has the highest boiling point? Explain. (b) Which solution has the highest pH? Explain. (c) Identify a pair of the solutions that would produce a precipitate when mixed together. Write the formula of the precipitate. (d) Which solution could be used to oxidize the Cl-(aq) ion? Identify the product of the oxidation. (e) Which solution would be the least effective conductor of electricity? Explain. Copyright © 2001 by College Entrance Examination Board. All rights reserved. Advanced Placement Program and AP are registered trademarks of the College Entrance Examination Board. GO ON TO THE NEXT PAGE. 10 2001 AP® CHEMISTRY FREE-RESPONSE QUESTIONS 3 I-(aq) + S2O82-(aq) “ I3-(aq) + 2 SO42-(aq) 6. Iodide ion, I-(aq), reacts with peroxydisulfate ion, S2O82-(aq), according to the equation above. Assume that the reaction goes to completion. (a) Identify the type of reaction (combustion, disproportionation, neutralization, oxidation-reduction, precipitation, etc.) represented by the equation above. Also, give the formula of another substance that could convert I-(aq) to I3-(aq). (b) In an experiment, equal volumes of 0.0120 M I-(aq) and 0.0040 M S2O82-(aq) are mixed at 25•C. The concentration of I3-(aq) over the following 80 minutes is shown in the graph below. (i) Indicate the time at which the reaction first reaches completion by marking an “X” on the curve above at the point that corresponds to this time. Explain your reasoning. (ii) Explain how to determine the instantaneous rate of formation of I3-(aq) at exactly 20 minutes. Draw on the graph above as part of your explanation. (c) Describe how to change the conditions of the experiment in part (b) to determine the order of the reaction with respect to I-(aq) and with respect to S2O82-(aq). (d) State clearly how to use the information from the results of the experiments in part (c) to determine the value of the rate constant, k, for the reaction. (e) On the graph below (which shows the results of the initial experiment as a dashed curve), draw in a curve for the results you would predict if the initial experiment were to be carried out at 35•C rather than at 25•C. Copyright © 2001 by College Entrance Examination Board. All rights reserved. Advanced Placement Program and AP are registered trademarks of the College Entrance Examination Board. GO ON TO THE NEXT PAGE. 11 2001 AP® CHEMISTRY FREE-RESPONSE QUESTIONS Answer EITHER Question 7 below OR Question 8 printed on page 13. Only one of these two questions will be graded. If you start both questions, be sure to cross out the question you do not want graded. The Section II score weighting for the question you choose is 15 percent. 7. Answer the following questions that refer to the galvanic cell shown in the diagram above. (A table of standard reduction potentials is printed on the green insert and on page 4 of the booklet with the pink cover.) (a) Identify the anode of the cell and write the half-reaction that occurs there. (b) Write the net ionic equation for the overall reaction that occurs as the cell operates and calculate the value o of the standard cell potential, E cell . (c) Indicate how the value of E cell would be affected if the concentration of Ni(NO3)2(aq) was changed from 1.0 M to 0.10 M and the concentration of Zn(NO3)2(aq) remained at 1.0 M. Justify your answer. (d) Specify whether the value of Keq for the cell reaction is less than 1, greater than 1, or equal to 1. Justify your answer. Copyright © 2001 by College Entrance Examination Board. All rights reserved. Advanced Placement Program and AP are registered trademarks of the College Entrance Examination Board. GO ON TO THE NEXT PAGE. 12 2001 AP® CHEMISTRY FREE-RESPONSE QUESTIONS 8. Account for each of the following observations about pairs of substances. In your answers, use appropriate principles of chemical bonding and/or intermolecular forces. In each part, your answer must include references to both substances. (a) Even though NH3 and CH4 have similar molecular masses, NH3 has a much higher normal boiling point (-33•C) than CH4 (-164•C). (b) At 25•C and 1.0 atm, ethane (C2H6) is a gas and hexane (C6H14) is a liquid. (c) Si melts at a much higher temperature (1,410•C) than Cl2 (-101•C). (d) MgO melts at a much higher temperature (2,852•C) than NaF (993•C). END OF EXAMINATION Copyright © 2001 by College Entrance Examination Board. All rights reserved. Advanced Placement Program and AP are registered trademarks of the College Entrance Examination Board. 13 ...
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