AP Chemistry 2006 Free-Response Questions Form B

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1 AP Chemistry 006 Free-Response Questions Form B The College Board: Connecting Students to College Success The College Board is a not-or-proit membership association whose mission is to connect students to college success and opportunity. Founded in 1900, the association is composed o more than 5,000 schools, colleges, universities, and other educational organizations. Each year, the College Board serves seven million students and their parents, 3,000 high schools, and 3,500 colleges through major programs and services in college admissions, guidance, assessment, inancial aid, enrollment, and teaching and learning. Among its best-known programs are the SAT, the PSAT/NMSQT, and the Advanced Placement Program (AP ). The College Board is committed to the principles o excellence and equity, and that commitment is embodied in all o its programs, services, activities, and concerns. 006 The College Board. All rights reserved. College Board, AP Central, APCD, Advanced Placement Program, AP, AP Vertical Teams, Pre-AP, SAT, and the acorn logo are registered trademarks o the College Board. Admitted Class Evaluation Service, CollegeEd, connect to college success, MyRoad, SAT Proessional Development, SAT Readiness Program, and Setting the Cornerstones are trademarks owned by the College Board. PSAT/NMSQT is a registered trademark o the College Board and National Merit Scholarship Corporation. All other products and services may be trademarks o their respective owners. Permission to use copyrighted College Board materials may be requested online at: Visit the College Board on the Web: AP Central is the oicial online home or the AP Program: apcentral.collegeboard.com.

2 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.

3 STANDARD REDUCTION POTENTIALS IN AQUEOUS SOLUTION AT 5 C Hal-reaction E ( V ) F ( g) e Æ F Co e - Æ Co Au 3 e - Æ Au( s ) 1.50 Cl ( g) e - Æ Cl O ( g) 4H 4e Æ HO( l ) Hg e - Æ Hg 0.9 Hg e - Æ Hg( l ) 0.85 Br ( l) e - Æ Br - Ag e - Æ Ag( s ) 0.80 Hg e - Æ Hg( l ) Fe e - Æ Fe 0.77 I ( s) e Æ I Cu e - Æ Cu( s ) 0.5 Cu e - Æ Cu( s ) 0.34 Cu e - Æ Cu Sn e - Æ Sn 0.15 S( s) H e - Æ HS( g ) 0.14 H e - Æ H ( g ) 0.00 Pb e - Æ Pb( s ) 0.13 Sn e - Æ Sn( s ) 0.14 Ni e - Æ Ni( s ) 0.5 Co e - Æ Co( s ) 0.8 Cd e - Æ Cd( s ) Cr e - Æ Cr 0.41 Fe e - Æ Fe( s ) Cr 3 e - Æ Cr( s ) 0.74 Zn e - Æ Zn( s ) 0.76 HO( l) e - Æ H ( g) OH 0.83 Mn e - Æ Mn( s ) Al 3 e - Æ Al( s ) 1.66 Be e - Æ Be( s ) 1.70 Mg e - Æ Mg( s ).37 Na e - Æ Na( s ).71 Ca e - Æ Ca( s ).87 Sr e - Æ Sr( s ).89 Ba e - Æ Ba( s ).90 Rb e - Æ Rb( s ).9 e - Æ ( s ).9 Cs e - Æ Cs( s ).9 Li e - Æ Li( s )

4 ADVANCED PLACEMENT CHEMISTRY EQUATIONS AND CONSTANTS ATOMIC STRUCTURE E hv c lv l h p mu mu En joule n EQUILIBRIUM [ H ][ A ] a [ HA] b w [ OH ][ HB ] [ B] 14 [ OH ][ H ] C 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 ( RT), p c Dn where Dn moles product gas moles reactant gas THERMOCHEMISTRY/INETICS DS S products - S reactants DH DH products - DH reactants DG DG products - DG reactants DG DH - TDS - RT ln RT log -n E DG DG RT ln Q DG 303. RT log Q q mcdt C p ln A ln k DH DT t Â Â Â - ln A -kt kt A A t 0 0 e j Ea - 1 ln A R T Â Â Â E energy u velocity v requency n principal quantum number l wavelength m mass p momentum Speed o light, c m s Planck s constant, h J s Boltzmann s constant, k J Avogadro s number mol Electron charge, e coulomb 1 electron volt per atom 96.5 kj mol Equilibrium Constants C E a b w p c p a (weak acid) (weak base) (water) (gas pressure) (molar concentrations) S standard entropy H standard enthalpy G standard ree energy E standard reduction potential T temperature n moles m mass q heat c speciic heat capacity molar heat capacity at constant pressure activation energy k rate constant A requency actor Faraday's constant, 96, 500 coulombs per mole o electrons -1-1 Gas constant, R 831. J mol L atm mol volt coulomb mol

5 GASES, LIQUIDS, AND SOLUTIONS PV nrt Ê naˆ Á P ( V - nb) nrt Ë V moles A PA Ptotal XA, where XA total moles Ptotal PA PB PC... m n M C 73 PV 1 1 PV T1 T m D V 3kT 3RT urms m M 1 E per molecule mu 3 E per mole RT r1 M r M1 molarity, M moles solute per liter solution molality moles solute per kilogram solvent DT i molality DTb ib molality p imrt A abc P pressure V volume T temperature n number o moles D density m mass u velocity urms root-mean-square speed E kinetic energy r rate o eusion M molar mass p osmotic pressure van't Ho actor molal reezing-point depression constant molal boiling-point elevation constant i b A a b c absorbance molar absorptivity path length concentration Q reaction quotient I current (amperes) q charge (coulombs) t time (seconds) E standard reduction potential equilibrium constant OXIDATION-REDUCTION; ELECTROCHEMISTRY c [ C] [ D] Q, where a A b B Æ c C d D a b [ A] [ B] q I t RT. E E - ln Q E 0059 cell cell cell - log 5 C n n log ne d Gas constant, R 831. J mol L atm mol 831. volt coulomb mol -3-1 Boltzmann's constant, k J -1 or H O 186. kg mol b or H O 051. kg mol 1atm 760 mm Hg 760 torr STP C and atm Faraday's constant, 96, 500 coulombs per mole o electrons 5

6 006 AP CHEMISTRY FREE-RESPONSE QUESTIONS (Form B) 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 i you do and you will receive little or no credit i you do not. Attention should be paid to signiicant igures. Be sure to write all your answers to the questions on the lined pages ollowing each question in the goldenrod booklet. Do NOT write your answers on the lavender insert. Answer Question 1 below. The Section II score weighting or this question is 0 percent. C 6 H 5 COOH(s) C 6 H 5 COO (aq) H (aq) a Benzoic acid, C 6 H 5 COOH, dissociates in water as shown in the equation above. A 5.0 ml sample o an aqueous solution o pure benzoic acid is titrated using standardized M NaOH. (a) Ater addition o 15.0 ml o the M NaOH, the ph o the resulting solution is Calculate each o the ollowing. (i) [H ] in the solution (ii) [OH ] in the solution (iii) The number o moles o NaOH added (iv) The number o moles o C 6 H 5 COO (aq) in the solution (v) The number o moles o C 6 H 5 COOH in the solution (b) State whether the solution at the equivalence point o the titration is acidic, basic, or neutral. Explain your reasoning. In a dierent titration, a g sample o a mixture o solid C 6 H 5 COOH and solid NaCl is dissolved in water and titrated with M NaOH. The equivalence point is reached when 4.78 ml o the base solution is added. (c) Calculate each o the ollowing. (i) The mass, in grams, o benzoic acid in the solid sample (ii) The mass percentage o benzoic acid in the solid sample 006 The College Board. All rights reserved. 6

7 006 AP CHEMISTRY FREE-RESPONSE QUESTIONS (Form B) Answer EITHER Question OR Question 3 below. Only one o these two questions will be graded. I you start both questions, be sure to cross out the question you do not want graded. The Section II score weighting or the question you choose is 0 percent.. Answer the ollowing questions about voltaic cells. (a) A voltaic cell is set up using Al /Al 3 as one hal-cell and Sn /Sn as the other hal-cell. The hal-cells contain equal volumes o solutions and are at standard conditions. (i) Write the balanced net-ionic equation or the spontaneous cell reaction. (ii) Determine the value, in volts, o the standard potential, E, or the spontaneous cell reaction. (iii) Calculate the value o the standard ree-energy change, G, or the spontaneous cell reaction. Include units with your answer. (iv) I the cell operates until [Al 3 ] is 1.08 M in the Al /Al 3 hal-cell, what is [Sn ] in the Sn /Sn hal-cell? (b) In another voltaic cell with Al /Al 3 and Sn /Sn hal-cells, [Sn ] is M and [Al 3 ] is 1.00 M. Calculate the value, in volts, o the cell potential, E cell, at 5 C. 3. Answer the ollowing questions about the thermodynamics o the reactions represented below. Reaction X: Reaction Y: 1 I (s) 1 Cl (g) ICl(g) D H 18 kj mol 1, DS J 1 mol 1 1 I (s) 1 Br (l) IBr(g) D H 41 kj mol 1, DS J 1 mol 1 (a) Is reaction X, represented above, spontaneous under standard conditions? Justiy your answer with a calculation. (b) Calculate the value o the equilibrium constant, eq, or reaction X at 5 C. (c) What eect will an increase in temperature have on the equilibrium constant or reaction X? Explain your answer. (d) Explain why the standard entropy change is greater or reaction Y than or reaction X. (e) Above what temperature will the value o the equilibrium constant or reaction Y be greater than 1.0? Justiy your answer with calculations. () For the vaporization o solid iodine, I (s) I (g), the value o DH 98 is 6 kj mol 1. Using this inormation, calculate the value o DH 98 or the reaction represented below. I (g) Cl (g) ICl(g) STOP I you inish beore time is called, you may check your work on this part only. Do not turn to the other part o the test until you are told to do so. 006 The College Board. All rights reserved. 7

8 006 AP CHEMISTRY FREE-RESPONSE QUESTIONS (Form B) CHEMISTRY Part B Time 50 minutes NO CALCULATORS MAY BE USED FOR PART B. Answer Question 4 below. The Section II score weighting or this question is 15 percent. 4. Write the ormulas to show the reactants and the products or any FIVE o the laboratory situations described below. Answers to more than ive 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 i the substances are extensively ionized. Omit ormulas or any ions or molecules that are unchanged by the reaction. You need not balance the equations. Example: A strip o magnesium is added to a solution o silver nitrate. (a) Solid calcium carbonate is strongly heated. (b) A strip o magnesium metal is placed in a solution o iron(ii) chloride. (c) Boron triluoride gas is mixed with ammonia gas. (d) Excess concentrated hydrochloric acid is added to a solution o nickel(ii) nitrate. (e) Solid ammonium chloride is added to a solution o potassium hydroxide. () Propanal is burned in air. (g) A strip o aluminum oil is placed in liquid bromine. (h) Solid copper(ii) sulide is strongly heated in air. 006 The College Board. All rights reserved. 8

9 006 AP CHEMISTRY FREE-RESPONSE QUESTIONS (Form B) Your responses to the rest o the questions in this part o the examination will be graded on the basis o the accuracy and relevance o the inormation cited. Explanations should be clear and well organized. Examples and equations may be included in your responses where appropriate. Speciic answers are preerable to broad, diuse responses. Answer BOTH Question 5 below AND Question 6 printed on page 11. Both o these questions will be graded. The Section II score weighting or these questions is 30 percent (15 percent each). 5. A student carries out an experiment to determine the equilibrium constant or a reaction by colorimetric (spectrophotometric) analysis. The production o the red-colored species FeSCN (aq) is monitored. (a) The optimum wavelength or the measurement o [FeSCN ] must irst be determined. The plot o absorbance, A, versus wavelength, λ, or FeSCN (aq) is given below. What is the optimum wavelength or this experiment? Justiy your answer. (b) A calibration plot or the concentration o FeSCN (aq) is prepared at the optimum wavelength. The data below give the absorbances measured or a set o solutions o known concentration o FeSCN (aq). Concentration (mol L 1 ) Absorbance The College Board. All rights reserved. 9

10 006 AP CHEMISTRY FREE-RESPONSE QUESTIONS (Form B) (i) Draw a Beer s law calibration plot o all the data on the grid below. Indicate the scale on the horizontal axis by labeling it with appropriate values. (ii) An FeSCN (aq) solution o unknown concentration has an absorbance o Use the plot you drew in part (i) to determine the concentration, in moles per liter, o this solution. (c) The purpose o the experiment is to determine the equilibrium constant or the reaction represented below. Fe 3 (aq) SCN (aq) FeSCN (aq) (i) Write the equilibrium-constant expression or c. (ii) The student combines solutions o Fe(NO 3 ) 3 and SCN to produce a solution in which the initial concentrations o Fe 3 (aq) and SCN (aq) are both M. The absorbance o this solution is measured, and the equilibrium FeSCN (aq) concentration is ound to be M. Determine the value o c. (d) I the student s equilibrium FeSCN (aq) solution o unknown concentration ades to a lighter color beore the student measures its absorbance, will the calculated value o c be too high, too low, or unaected? Justiy your answer. 006 The College Board. All rights reserved. 10

11 006 AP CHEMISTRY FREE-RESPONSE QUESTIONS (Form B) GeCl 4 SeCl 4 ICl 4 ICl 4 6. The species represented above all have the same number o chlorine atoms attached to the central atom. (a) Draw the Lewis structure (electron-dot diagram) o each o the our species. Show all valence electrons in your structures. (b) On the basis o the Lewis structures drawn in part (a), answer the ollowing questions about the particular species indicated. (i) What is the Cl Ge Cl bond angle in GeCl 4? (ii) Is SeCl 4 polar? Explain. (iii) What is the hybridization o the I atom in ICl 4? (iv) What is the geometric shape ormed by the atoms in ICl 4? 006 The College Board. All rights reserved. 11

12 006 AP CHEMISTRY FREE-RESPONSE QUESTIONS (Form B) Answer EITHER Question 7 OR Question 8 below. Only one o these two questions will be graded. I you start both questions, be sure to cross out the question you do not want graded. The Section II score weighting or the question you choose is 15 percent. 7. Account or each o the ollowing observations in terms o atomic theory and/or quantum theory. (a) Atomic size decreases rom Na to Cl in the periodic table. (b) Boron commonly orms molecules o the type BX 3. These molecules have a trigonal planar structure. (c) The irst ionization energy o is less than that o Na. (d) Each element displays a unique gas-phase emission spectrum. 8. Use chemical and physical principles to account or each o the ollowing. (a) An aluminum container illed with an aqueous solution o CuSO 4 eventually developed a leak. Include a chemical equation with your answer. (b) The inside o a metal container was cleaned with steam and immediately sealed. Later, the container imploded. (c) Skin eels cooler ater rubbing alcohol has been applied to it. (d) The redness and itching o the skin caused by ant bites (injections o methanoic acid, HCO H) can be relieved by applying a paste made rom water and baking soda (solid sodium hydrogen carbonate). Include a chemical equation with your answer. STOP END OF EXAM 006 The College Board. All rights reserved. 1

AP Chemistry 2008 Free-Response Questions Form B

AP Chemistry 2008 Free-Response Questions Form B AP Chemistry 008 Free-Response Questions Form B The College Board: Connecting Students to College Success The College Board is a not-for-profit membership association whose mission is to connect students