AP Chemistry 2001 Free-Response Questions

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1 AP Chemistry 001 FreeResponse 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 facetoface 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 thirdparty 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,,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 bestknown 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 001 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

2 INFORMATION IN THE TABLE BELOW AND IN THE TABLES ON PAGES 35 MAY BE USEFUL IN ANSWERING THE QUESTIONS IN THIS SECTION OF THE EXAMINATION DO NOT DETACH FROM BOO 1 H Li Na Rb Cs Fr (3) 4 Be Mg Ca PERIODIC TABLE OF THE ELEMENTS Sr Ba Ra 60 1 Sc Y *La Ac 703 Ti Zr 91 7 Hf V Nb Ta Cr Mo W Mn Tc (98) 75 Re Fe Ru Os Co Rh Ir Rf Db Sg Bh Hs Mt (61) (6) (63) (6) (65) (66) 8 Ni Pd Pt (69) 9 Cu Ag Au (7) 30 Zn Cd Hg (77) 5 B Al Ga In Tl C Si Ge Sn Pb 07 7 N P As Sb Not yet named Bi O S Se Te Po (09) 9 F Cl Br I At (10) *Lanthanide Series Actinide Series Ce Pr Nd Pm Sm Eu Gd Tb Dy Ho Er Tm Yb Lu (145) Th Pa U Np Pu Am Cm Bk Cf Es Fm Md No Lr (44) (43) (47) (47) (51) (5) (57) (58) (59) (60) He Ne Ar r Xe Rn () GO ON TO THE NEXT PAGE

3 STANDARD REDUCTION POTENTIALS IN AQUEOUS SOLUTION AT 5 C Halfreaction E ( V) Li e Li() s 305 Cs e Cs() s 9 e () s 9 Rb e Rb() s 9 Ba e Ba() s 90 Sr e Sr() s 89 Ca e Ca() s 87 Na e Na() s 71 Mg e Mg( s) 37 Be e Be() s Al 3 e Al() s 166 Mn e Mn() s 118 Zn e Zn() s Cr 3 e Cr() s 074 Fe e Fe() s Cr e Cr 041 Cd e Cd() s 040 Tl e Tl() s 034 Co e Co( s) 08 Ni e Ni() s 05 Sn e Sn() s 014 Pb e Pb() s 013 H e H ( g) 000 S () s H e HS ( g) Sn e Sn 015 Cu e Cu 015 Cu e Cu() s 034 Cu e Cu() s 05 I () s e I Fe e Fe 077 Hg e Hg( l) 079 Ag e Ag( s) 080 Hg e Hg( l) 085 Hg e Hg 09 Br l e () Br 107 O ( g) 4 H 4 e HO( l) 13 Cl ( g) e Cl Au 3 e Au() s Co e Co 18 F ( g) e F 87 3 GO ON TO THE NEXT PAGE

4 ADVANCED PLACEMENT CHEMISTRY EQUATIONS AND CONSTANTS ATOMIC STRUCTURE DE E c l hv v h mu p mu n l n joule E v l p u n m energy frequency wavelength momentum velocity principal quantum number mass EQUILIBRIUM a b w [ H ][ A ] [ HA] [ OH ][ HB ] [ B] 14 [ OH ][ H ] 10 5oC a b ph log [ H ], poh log [ OH ] 14 ph poh log [ A ph p ] a [ HA] log [ HB poh p ] b [ B] p log, p log a a b b D ( RT), p c n where Dn moles product gas moles reactant gas THERMOCHEMISTRY DSo So products So reactants DHo DHo products DHo reactants DGo DGo products DGo reactants DGo DHo TDSo RT ln 303 RT log n E DG DGo RT ln Q DGo 303 RT log Q q mcdt C p DH DT f f o f f 8 1 Speed of light, c m s 34 Planck s constant, h J s 3 1 Boltzmann s constant, k J Avogadro s number molecules mol 19 Electron charge, e coulomb 1 electron volt per atom 96 5 kj mol Equilibrium Constants a b w p c C p (weak acid) (weak base) (water) (gas pressure) (molar concentrations) So standard entropy Ho standard enthalpy Go standard free energy E o standard reduction potential T temperature n moles m mass q heat c specific heat capacity molar heat capacity at constant pressure 1faraday 96500, coulombs 4 GO ON TO THE NEXT PAGE

5 GASES, LIQUIDS, AND SOLUTIONS PV nrt n a P V nb nrt V ( ) moles A PA Ptotal X A, where X A total moles Ptotal PA PB PC n m M oc 73 PV 1 1 PV T1 T m D V 3kT 3RT urms m M E per molecule 1 mu E per mole 3 RT r1 M r M1 molarity, M moles solute per liter solution molality moles solute per kilogram solvent DTf if molality DTb ib molality p nrt V i OXIDATIONREDUCTION; ELECTROCHEMISTRY c d [ C] [ D] Q, where a A b B c C d D a b [ A] [ B] I q t Ecell RT E o ln Q E o cell cell log 5 o C n n log ne o u P pressure V volume T temperature n number of moles D density m mass u velocity rms E r M p i Q I q t E f b o rootmeansquare speed kinetic energy rate of effusion molar mass osmotic pressure van t Hoff factor molal freezingpoint depression constant molal boilingpoint elevation constant reaction quotient current (amperes) charge (coulombs) time (seconds) standard reduction potential equilibrium constant Gas constant, R 831 J mol f b Faraday s constant, L atm mol Boltzmann s constant, k for H O 186 kg mol J for H O 051 kg mol volt coulomb mol STP 0 000oC and atm , 500 coulombs per mole of electrons 5 GO ON TO THE NEXT PAGE

6 001 AP CHEMISTRY FREERESPONSE 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 0 percent 1 Answer the following questions relating to the solubility of the chlorides of silver and lead (a) At 10 C, 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 solubilityproduct constant, sp, for AgCl(s) at 10 C (b) At 5 C, the value of sp for PbCl (s) is and the value of sp for AgCl(s) is (i) If 600 ml of M NaCl(aq) is added to 600 ml of M Pb(NO 3 ) (aq), will a precipitate form? Assume that volumes are additive Show calculations to support your answer (ii) Calculate the equilibrium value of [Pb (aq)] in 100 L of saturated PbCl solution to which 050 mole of NaCl(s) has been added Assume that no volume change occurs (iii) If 0100 M NaCl(aq) is added slowly to a beaker containing both 010 M AgNO 3 (aq) and 0150 M Pb(NO 3 ) (aq) at 5 C, which will precipitate first, AgCl(s) or PbCl (s)? Show calculations to support your answer Copyright 001 by College Entrance Examination Board All rights reserved Advanced Placement Program and AP are registered trademarks of the College Entrance Examination Board 6 GO ON TO THE NEXT PAGE

7 001 AP CHEMISTRY FREERESPONSE QUESTIONS Answer EITHER Question 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 0 percent NO(g) O (g) NO (g) H 1141 kj, S 1465 J 1 The reaction represented above is one that contributes significantly to the formation of photochemical smog (a) Calculate the quantity of heat released when 731 g of NO(g) is converted to NO (g) (b) For the reaction at 5 C, the value of the standard freeenergy change, DG, is 704 kj (i) Calculate the value of the equilibrium constant, eq, for the reaction at 5 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 O (g) at 5 C Standard Molar Entropy, S (J 1 mol 1 ) NO(g) 108 NO (g) 401 (d) Use the data in the table below to calculate the bond energy, in kj mol 1, of the nitrogenoxygen bond in NO Assume that the bonds in the NO molecule are equivalent (ie, they have the same energy) Bond Energy (kj mol 1 ) Nitrogenoxygen bond in NO 607 Oxygenoxygen bond in O 495 Nitrogenoxygen bond in NO? Copyright 001 by College Entrance Examination Board All rights reserved Advanced Placement Program and AP are registered trademarks of the College Entrance Examination Board 7 GO ON TO THE NEXT PAGE

8 001 AP CHEMISTRY FREERESPONSE 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 35 mg, yet the tablet has a mass of 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 3000 g of the pure compound yields 100 g of water and 37 L of dry carbon dioxide, measured at 750 mm Hg and 5 C Calculate the mass, in g, of each element in the 3000 g sample (c) A student dissolved 165 g of pure acetylsalicylic acid in distilled water and titrated the resulting solution to the equivalence point using 8843 ml of 010 M NaOH(aq) Assuming that acetylsalicylic acid has only one ionizable hydrogen, calculate the molar mass of the acid (d) A mole sample of pure acetylsalicylic acid was dissolved in 1500 ml of water and then titrated with 0100 M NaOH(aq) The equivalence point was reached after 000 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, a, for acetylsalicylic acid and (ii) the ph of the solution after a total volume of 500 ml of the NaOH solution had been added (assume that volumes are additive) Volume of 0100 M NaOH Added (ml) ph ? Copyright 001 by College Entrance Examination Board All rights reserved Advanced Placement Program and AP are registered trademarks of the College Entrance Examination Board 8 GO ON TO THE NEXT PAGE

9 001 AP CHEMISTRY FREERESPONSE 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 001 by College Entrance Examination Board All rights reserved Advanced Placement Program and AP are registered trademarks of the College Entrance Examination Board 9 GO ON TO THE NEXT PAGE

10 001 AP CHEMISTRY FREERESPONSE 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 5 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 001 by College Entrance Examination Board All rights reserved Advanced Placement Program and AP are registered trademarks of the College Entrance Examination Board 10 GO ON TO THE NEXT PAGE

11 001 AP CHEMISTRY FREERESPONSE QUESTIONS 3 I (aq) S O 8 (aq) I 3 (aq) SO 4 (aq) 6 Iodide ion, I (aq), reacts with peroxydisulfate ion, S O 8 (aq), according to the equation above Assume that the reaction goes to completion (a) Identify the type of reaction (combustion, disproportionation, neutralization, oxidationreduction, precipitation, etc) represented by the equation above Also, give the formula of another substance that could convert I (aq) to I 3 (aq) (b) In an experiment, equal volumes of 0010 M I (aq) and M S O 8 (aq) are mixed at 5 C The concentration of I 3 (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 I 3 (aq) at exactly 0 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 S O 8 (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 5 C Copyright 001 by College Entrance Examination Board All rights reserved Advanced Placement Program and AP are registered trademarks of the College Entrance Examination Board 11 GO ON TO THE NEXT PAGE

12 001 AP CHEMISTRY FREERESPONSE 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 halfreaction that occurs there (b) Write the net ionic equation for the overall reaction that occurs as the cell operates and calculate the value of the standard cell potential, E o cell (c) Indicate how the value of E cell would be affected if the concentration of Ni(NO 3 ) (aq) was changed from 10 M to 010 M and the concentration of Zn(NO 3 ) (aq) remained at 10 M Justify your answer (d) Specify whether the value of eq for the cell reaction is less than 1, greater than 1, or equal to 1 Justify your answer Copyright 001 by College Entrance Examination Board All rights reserved Advanced Placement Program and AP are registered trademarks of the College Entrance Examination Board 1 GO ON TO THE NEXT PAGE

13 001 AP CHEMISTRY FREERESPONSE 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 NH 3 and CH 4 have similar molecular masses, NH 3 has a much higher normal boiling point (33 C) than CH 4 (164 C) (b) At 5 C and 10 atm, ethane (C H 6 ) is a gas and hexane (C 6 H 14 ) is a liquid (c) Si melts at a much higher temperature (1,410 C) than Cl (101 C) (d) MgO melts at a much higher temperature (,85 C) than NaF (993 C) END OF EXAMINATION Copyright 001 by College Entrance Examination Board All rights reserved Advanced Placement Program and AP are registered trademarks of the College Entrance Examination Board 13