AP® Chemistry
2012 Free-Response Questions
About the College Board
The College Board is a mission-driven not-for-profit organization that connects students to college success and opportunity. Founded in 1900, the College Board was created to expand access to higher education. Today, the membership association is made up of more than 5,900 of the world’s leading educational institutions and is dedicated to promoting excellence and equity in education. Each year, the College Board helps more than seven million students prepare for a successful transition to college through programs and services in college readiness and college success — including the SAT® and the Advanced Placement Program®. The organization also serves the education community through researc
h and advocacy on behalf of students, educators, and schools.
© 2012 The College Board. College Board, Advanced Placement Program, AP, AP Central, SAT, and the acorn logo are registered trademarks of the College Board. Admitted Class Evaluation Service and inspiring minds are trademarks owned by the College Board. All other products and services may be trademarks of their respective owners. Visit the College Board on the Web: Permission to use copyrighted College Board materials may be requested online at:
Visit the College Board on the Web: reaction mass
AP Central is the official online home for the AP Program:
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.
STANDARD REDUCTION POTENTIALS IN AQUEOUS SOLUTION AT 25C ∞
Half-reaction
(V)E ∞
2F ()2g e -+ Æ 2F -    2.87 3+Co e -+ Æ 2Co +    1.82 3+Au 3e -+ Æ Au()s    1.50 2Cl ()2g e -+ Æ 2Cl -    1.36 +2O ()4H 4g e -++ Æ 22H O()l    1.23 2Br ()2l e -+ Æ 2Br -    1.07 2+2Hg 2e -+ Æ 2+2Hg
0.92 2+Hg 2e -+ Æ Hg()l  0.85 +Ag e -+ Æ Ag()s  0.80 2+2Hg 2e -+ Æ 2Hg()l  0.79 3+Fe e -+ Æ 2+Fe  0.77 2I ()2s e -+ Æ 2I - 0.53 +Cu e -+ Æ Cu()s  0.52 2+Cu 2e -+ Æ Cu()s  0.34 2+Cu e -+ Æ +Cu  0.15 4+Sn 2e -+ Æ 2+Sn  0.15 +S()2H 2s e -++ Æ 2H S()g  0.14 +2H 2e -+ Æ 2H ()g  0.00 2+Pb 2e -+ Æ Pb()s  –0.13 2+Sn 2e -+ Æ Sn()s  –0.14 2+Ni 2e -+ Æ Ni()s  –0.25 2+Co 2e -+ Æ Co()s  –0.28 2+Cd 2e -+ Æ Cd()s  –0.40 3+Cr e -+ Æ 2+Cr  –0.41 2+Fe 2e -+ Æ Fe()s  –0.44 3+Cr 3e -+ Æ Cr()s  –0.74 2+Zn 2e -+ Æ Zn()s  –0.76 22H O()2l e -+ Æ 2H () + 2OH g -–0.83 2+Mn 2e -+ Æ Mn()s  –1.18 3+Al 3e -+ Æ Al()s  –1.66 2+Be 2e -+ Æ Be()s  –1.70 2+Mg 2e -+ Æ Mg()s  –2.37 +Na e -+ Æ Na()s  –2.71 2+Ca 2e -+ Æ Ca()s  –2.87 2+Sr 2e -+ Æ Sr()s
–2.89 2+Ba 2e -+ Æ Ba()s  –2.90 +Rb e -+ Æ Rb()s  –2.92 +K e -+ Æ K()s  –2.92 +Cs e -+ Æ Cs()s  –2.92 +Li e -+
Æ Li()s
–3.05
ADVANCED PLACEMENT CHEMISTRY EQUATIONS AND CONSTANTS
pressure volume temperature
number of moles density mass velocity
P V T n D m =======
u
root-mean-square speed kinetic energy rate of effusion molar mass
osmotic pressure van’t Hoff factor
molal freezing-point depression constant molal boiling-point elevation constant abs rms f
b u KE r i K K A p =========M orbance
molar absorptivity path length concentration reaction quotient current (amperes)charge (coulombs)time (seconds)
standard reduction potential equilibrium constant
a b c Q I q t
E K =======
==D
11
1111
11
231
121
2  1atm 7Gas constant, 8.31 J mol K 0.0821 L atm mol K 62.4L torr mol K  8.31 volt coulomb mol K Boltzmann’s constant,    1.3810J K for H O    1.86 K kg mol for H O 0.512 K kg mol f b R k K K ------------======¥==60mm Hg
760torr
STP 0.00C and 1.0 atm
Faraday’s constant, 96,500coulombs per mole
of electrons
===D Ᏺ
2012 AP ® CHEMISTRY FREE-RESPONSE QUESTIONS
© 2012 The College Board.
Visit the College Board on the Web:
CHEMISTRY
Section II
(Total time—95 minutes)
Part A
Time—55 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 this booklet.
Answer Questions 1, 2, and 3. The Section II score weighting for each question is 20 percent.
1. A 1.22 g sample of a pure monoprotic acid, HA, was dissolved in distilled water. The  HA  solution was then
titrated with 0.250 M  NaOH. The pH was measured throughout the titration, and the equivalence point was reached when 40.0 mL of the  NaOH  solution had been added. The data from the titration are recorded in the table below.
Volume of 0.250 M  NaOH
Added (mL)
pH of Titrated Solution
0.00 ? 10.0    3.72 20.0    4.20 30.0 ? 40.0 8.62 50.0
12.40
(a) Explain how the data in the table above provide evidence that  HA  is a weak acid rather than a strong acid. (b) Write the balanced net-ionic equation for the reaction that occurs when the solution of  NaOH  is added to the
solution of  HA. (c) Calculate the number of moles of  HA  that were titrated. (d) Calculate the molar mass of  HA.
The equation for the dissociation reaction of  HA  in water is shown below.
HA(aq )  +  H 2O(l )  ƨ  H 3
O +(aq )  +  A −(aq ) K a  =  6.3 × 10−5 (e) Assume that the initial concentration of the  HA  solution (before any  NaOH  solution was added) is 0.200 M.
Determine the pH of the initial  HA  solution.  (f) Calculate the value of  [H 3O +] in the solution after 30.0 mL of  NaOH  solution is added and the total volume
of the solution is 80.0 mL.

版权声明：本站内容均来自互联网，仅供演示用，请勿用于商业和其他非法用途。如果侵犯了您的权益请与我们联系QQ:729038198，我们将在24小时内删除。