2000 Advanced Placement Program Free-Response Questions

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1 000 Advanced Placement Program 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 3,800 schools, colleges, universities, and other educational organizations Each year, the College Board serves over three million students and their parents,,000 high schools, and 5,000 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 000 by College Entrance Examination Board and Educational Testing Service 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 GO ON TO THE NEXT PAGE 5

6 000 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 STEPS INVOLVED IN ARRIVING AT YOUR ANSWERS It is to your advantage to do this, because you may earn 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 this booklet Answer Question 1 below The Section II score weighting for this question is 0 percent H S(g) H (g) S (g) 1 When heated, hydrogen sulfide gas decomposes according to the equation above A 340 g sample of H S(g) is introduced into an evacuated rigid 15 L container The sealed container is heated to 483, and mol of S (g) is present at equilibrium (a) Write the expression for the equilibrium constant, c, for the decomposition reaction represented above (b) Calculate the equilibrium concentration, in mol L 1, of the following gases in the container at 483 (i) H (g) (ii) H S(g) (c) Calculate the value of the equilibrium constant, c, for the decomposition reaction at 483 (d) Calculate the partial pressure of S (g) in the container at equilibrium at 483 (e) For the reaction H (g) 1 S (g) H S(g) at 483, calculate the value of the equilibrium constant, c Copyright 000 College Entrance Examination Board and Educational Testing Service All rights reserved AP is a registered trademark of the College Entrance Examination Board 6 GO ON TO THE NEXT PAGE

7 000 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 Answer the following questions that relate to electrochemical reactions (a) Under standard conditions at 5 C, Zn(s) reacts with Co (aq) to produce Co(s) (i) Write the balanced equation for the oxidation half reaction (ii) Write the balanced netionic equation for the overall reaction (iii) Calculate the standard potential, E, for the overall reaction at 5 C (b) At 5 C, H O decomposes according to the following equation H O (aq) H O(l) O (g) E 055 V (i) Determine the value of the standard free energy change, G, for the reaction at 5 C (ii) Determine the value of the equilibrium constant, eq, for the reaction at 5 C (iii) The standard reduction potential, E, for the half reaction O (g) 4 H (aq) 4 e H O(l) has a value of 13 V Using this information in addition to the information given above, determine the value of the standard reduction potential, E, for the half reaction below O (g) H (aq) e H O (aq) (c) In an electrolytic cell, Cu(s) is produced by the electrolysis of CuSO 4 (aq) Calculate the maximum mass of Cu(s) that can be deposited by a direct current of 100 amperes passed through 500 L of 00 M CuSO 4 (aq) for a period of 100 hour Copyright 000 College Entrance Examination Board and Educational Testing Service All rights reserved AP is a registered trademark of the College Entrance Examination Board 7 GO ON TO THE NEXT PAGE

8 000 AP CHEMISTRY FREERESPONSE QUESTIONS 3 Answer the following questions about BeC O 4 (s) and its hydrate (a) Calculate the mass percent of carbon in the hydrated form of the solid that has the formula BeC O 4 3 H O (b) When heated to 0 C, BeC O 4 3 H O(s) dehydrates completely as represented below BeC O 4 3 H O(s) BeC O 4 (s) 3 H O(g) If 31 g of BeC O 4 3 H O(s) is heated to 0 C, calculate (i) the mass of BeC O 4 (s) formed, and, (ii) the volume of the H O(g) released, measured at 0 C and 735 mm Hg (c) A 0345 g sample of anhydrous BeC O 4, which contains an inert impurity, was dissolved in sufficient water to produce 100 ml of solution A 00 ml portion of the solution was titrated with MnO 4 (aq) The balanced equation for the reaction that occurred is as follows 16 H (aq) MnO 4 (aq) 5 C O 4 (aq) Mn (aq) 10 CO (g) 8 H O(l) The volume of M MnO 4 (aq) required to reach the equivalence point was 1780 ml (i) Identify the reducing agent in the titration reaction (ii) For the titration at the equivalence point, calculate the number of moles of each of the following that reacted MnO 4 (aq) C O 4 (aq) (iii) Calculate the total number of moles of C O 4 (aq) that were present in the 100 ml of prepared solution (iv) Calculate the mass percent of BeC O 4 (s) in the impure 0345 g sample Copyright 000 College Entrance Examination Board and Educational Testing Service All rights reserved AP is a registered trademark of the College Entrance Examination Board 8 GO ON TO THE NEXT PAGE

9 000 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) A small piece of calcium metal is added to hot distilled water (b) Butanol is burned in air (c) Excess concentrated ammonia solution is added to a solution of nickel(ii) sulfate (d) A solution of copper(ii) chloride is added to a solution of sodium sulfide (e) A solution of tin(ii) nitrate is added to a solution of silver nitrate (f) Excess hydrobromic acid solution is added to a solution of potassium hydrogen carbonate (g) Powdered strontium oxide is added to distilled water (h) Carbon monoxide gas is passed over hot iron(iii) oxide Copyright 000 College Entrance Examination Board and Educational Testing Service All rights reserved AP is a registered trademark of the College Entrance Examination Board 9 GO ON TO THE NEXT PAGE

10 000 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 The molar mass of an unknown solid, which is nonvolatile and a nonelectrolyte, is to be determined by the freezingpoint depression method The pure solvent used in the experiment freezes at 10 C and has a known molal freezingpoint depression constant, f Assume that the following materials are also available œ test tubes œ stirrer œ pipet œ thermometer œ balance œ beaker œ stopwatch œ graph paper œ hotwater bath œ ice (a) Using the two sets of axes provided below, sketch cooling curves for (i) the pure solvent and for (ii) the solution as each is cooled from 0 C to 00 C (b) Information from these graphs may be used to determine the molar mass of the unknown solid (i) Describe the measurements that must be made to determine the molar mass of the unknown solid by this method (ii) Show the setup(s) for the calculation(s) that must be performed to determine the molar mass of the unknown solid from the experimental data (iii) Explain how the difference(s) between the two graphs in part (a) can be used to obtain information needed to calculate the molar mass of the unknown solid (c) Suppose that during the experiment a significant but unknown amount of solvent evaporates from the test tube What effect would this have on the calculated value of the molar mass of the solid (ie, too large, too small, or no effect)? Justify your answer (d) Show the setup for the calculation of the percentage error in a student s result if the student obtains a value of 16 g mol 1 for the molar mass of the solid when the actual value is 10 g mol 1 Copyright 000 College Entrance Examination Board and Educational Testing Service All rights reserved AP is a registered trademark of the College Entrance Examination Board 10 GO ON TO THE NEXT PAGE

11 000 AP CHEMISTRY FREERESPONSE QUESTIONS 6 Consider the reaction represented above O 3 (g) NO(g) O (g) NO (g) (a) Referring to the data in the table below, calculate the standard enthalpy change, H, for the reaction at 5 C Be sure to show your work Standard enthalpy of formation, DH f o, at 5 C O 3 (g) NO(g) NO (g) (kj mol 1 ) (b) Make a qualitative prediction about the magnitude of the standard entropy change, S, for the reaction at 5 C Justify your answer (c) On the basis of your answers to parts (a) and (b), predict the sign of the standard freeenergy change, G, for the reaction at 5 C Explain your reasoning (d) Use the information in the table below to write the ratelaw expression for the reaction, and explain how you obtained your answer Experiment Number Initial [O 3 ] (mol L 1 ) Initial [NO] (mol L 1 ) Initial Rate of Formation of NO (mol L 1 s 1 ) x x x x (e) The following threestep mechanism is proposed for the reaction Identify the step that must be the slowest in order for this mechanism to be consistent with the ratelaw expression derived in part (d) Explain Step I: O 3 NO O NO 3 Step II: O O 3 O Step III: NO 3 NO NO Copyright 000 College Entrance Examination Board and Educational Testing Service All rights reserved AP is a registered trademark of the College Entrance Examination Board 11 GO ON TO THE NEXT PAGE

12 000 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 about the element selenium, Se (atomic number 34) (a) Samples of natural selenium contain six stable isotopes In terms of atomic structure, explain what these isotopes have in common, and how they differ (b) Write the complete electron configuration (eg, 1s s etc) for a selenium atom in the ground state Indicate the number of unpaired electrons in the groundstate atom, and explain your reasoning (c) In terms of atomic structure, explain why the first ionization energy of selenium is (i) less than that of bromine (atomic number 35), and (ii) greater than that of tellurium (atomic number 5) (d) Selenium reacts with fluorine to form SeF 4 Draw the complete Lewis electrondot structure for SeF 4 and sketch the molecular structure Indicate whether the molecule is polar or nonpolar, and justify your answer Copyright 000 College Entrance Examination Board and Educational Testing Service All rights reserved AP is a registered trademark of the College Entrance Examination Board 1 GO ON TO THE NEXT PAGE

13 000 AP CHEMISTRY FREERESPONSE QUESTIONS 8 A volume of 300 ml of 010 M NH 3 (aq) is titrated with 00 M HCl(aq) The value of the basedissociation constant, b, for NH 3 in water is at 5 C (a) Write the netionic equation for the reaction of NH 3 (aq) with HCl(aq) (b) Using the axes provided below, sketch the titration curve that results when a total of 400 ml of 00 M HCl(aq) is added dropwise to the 300 ml volume of 010 M NH 3 (aq) (c) From the table below, select the most appropriate indicator for the titration Justify your choice Indicator p a Methyl Red 55 Bromothymol Blue 71 Phenolphthalein 87 (d) If equal volumes of 010 M NH 3 (aq) and 010 M NH 4 Cl(aq) are mixed, is the resulting solution acidic, neutral, or basic? Explain END OF EXAMINATION Copyright 000 College Entrance Examination Board and Educational Testing Service All rights reserved AP is a registered trademark of the College Entrance Examination Board 13