Advanced 2000 Placement Program
Free-Response Questions
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22
8
9
27
28
29
30
-2-
Ba
Cs
*La
57
Zr
Hf
72
91.22
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
85.47
40
39
38
37
Ti
47.90
44.96
Ca
40.08
K
39.10
(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
30.974
33
28.09
32
26.98
31
Ar
18
Kr
I
Te
Sb
Sn
Xe
54
In
53
50
49
52
72.59
69.72
51
83.80
Br
79.90
Se
78.96
As
74.92
Ge
36
35
35.453 39.948
Cl
17
Ga
34
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
Sc
26
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 25C
E ( V )
Half-reaction
Li + + e -
+
K + 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
+
e-
+
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
Ka =
Speed of light, c = 3.0 10 8 m s 1
[H + ] [A ]
[ HA ]
Plancks constant, h = 6.63 10 34 J s
[OH ] [ HB + ]
Kb =
[ B]
Boltzmanns constant, k = 1.38 10 23 J K 1
Avogadros 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
G o = standard free energy
S o products S o reactants
= DHfo products DH fo reactants
= DGfo products DGfo reactants
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
1 faraday
DG = DG o + RT ln Q = DG o + 2.303 RT log Q
q = mcDT
DH
Cp =
DT
=
=
=
=
=
=
=
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
vant 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
OXIDATION-REDUCTION; ELECTROCHEMISTRY
Boltzmanns constant, k = 1.38 10 23 J K 1
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
Faradays constant,
= 96,500 coulombs per mole
of electrons
nE o
0.0592
GO ON TO THE NEXT PAGE.
-5-
2000 AP CHEMISTRY FREE-RESPONSE QUESTIONS
CHEMISTRYSECTION II
(Total time90 minutes)
Part A
Time40 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 20 percent.
2 H2S(g) 2 H2(g) + S2(g)
1. When heated, hydrogen sulfide gas decomposes according to the equation above. A 3.40 g sample of H2S(g) is
introduced into an evacuated rigid 1.25 L container. The sealed container is heated to 483 K, and 3.72 102 mol
of S2(g) is present at equilibrium.
(a) Write the expression for the equilibrium constant, Kc , for the decomposition reaction represented above.
(b) Calculate the equilibrium concentration, in mol L-1, of the following gases in the container at 483 K.
(i) H2(g)
(ii) H2S(g)
(c) Calculate the value of the equilibrium constant, Kc , for the decomposition reaction at 483 K.
(d) Calculate the partial pressure of S2(g) in the container at equilibrium at 483 K.
(e) For the reaction H2(g) + 1 S2(g) H2S(g) at 483 K, calculate the value of the equilibrium constant, Kc .
2
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AP is a registered trademark of the College Entrance Examination Board.
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-6-
2000 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.
2. Answer the following questions that relate to electrochemical reactions.
(a) Under standard conditions at 25C, Zn(s) reacts with Co2+(aq) to produce Co(s).
(i) Write the balanced equation for the oxidation half reaction.
(ii) Write the balanced net-ionic equation for the overall reaction.
(iii) the Calculate standard potential, E, for the overall reaction at 25C.
(b) At 25C, H2O2 decomposes according to the following equation.
2 H2O2(aq) 2 H2O(l) + O2(g)
E = 0.55 V
(i) Determine the value of the standard free energy change, G , for the reaction at 25C.
(ii) Determine the value of the equilibrium constant, Keq , for the reaction at 25C.
(iii) The standard reduction potential, E, for the half reaction O2(g) + 4 H+(aq) + 4 e 2 H2O(l) has a
value of 1.23 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.
O2(g) + 2 H+(aq) + 2 e- H2O2(aq)
(c) In an electrolytic cell, Cu(s) is produced by the electrolysis of CuSO4(aq). Calculate the maximum mass of
Cu(s) that can be deposited by a direct current of 100. amperes passed through 5.00 L of 2.00 M CuSO4(aq)
for a period of 1.00 hour.
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AP is a registered trademark of the College Entrance Examination Board.
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-7-
2000 AP CHEMISTRY FREE-RESPONSE QUESTIONS
3. Answer the following questions about BeC2O4(s) and its hydrate.
(a) Calculate the mass percent of carbon in the hydrated form of the solid that has the formula BeC2O4 3 H2O
(b) When heated to 220.C, BeC2O4 3 H2O(s) dehydrates completely as represented below.
BeC2O4 3 H2O(s) BeC2O4(s) + 3 H2O(g)
If 3.21 g of BeC2O4 3 H2O(s) is heated to 220.C, calculate
(i) the mass of BeC2O4(s) formed, and,
(ii) the volume of the H2O(g) released, measured at 220.C and 735 mm Hg.
(c) A 0.345 g sample of anhydrous BeC2O4 , which contains an inert impurity, was dissolved in sufficient water
to produce 100. mL of solution. A 20.0 mL portion of the solution was titrated with KMnO4(aq). The
balanced equation for the reaction that occurred is as follows.
16 H+(aq) + 2 MnO4-(aq) + 5 C2O42-(aq) 2 Mn2+(aq) + 10 CO2(g) + 8 H2O(l).
The volume of 0.0150 M KMnO4(aq) required to reach the equivalence point was 17.80 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.
MnO4-(aq)
C2O42-(aq)
(iii) Calculate the total number of moles of C2O42-(aq) that were present in the 100. mL of prepared
solution.
(iv) Calculate the mass percent of BeC2O4(s) in the impure 0.345 g sample.
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-8-
2000 AP CHEMISTRY FREE-RESPONSE QUESTIONS
CHEMISTRY
Part B
Time50 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.
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-9-
2000 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. The molar mass of an unknown solid, which is nonvolatile and a nonelectrolyte, is to be determined by the
freezing-point depression method. The pure solvent used in the experiment freezes at 10C and has a known
molal freezing-point depression constant, Kf . Assume that the following materials are also available.
test tubes
beaker
stirrer
stopwatch
pipet
graph paper
thermometer
hot-water bath
balance
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 20C to 0.0C.
(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 (i.e., too large, too
small, or no effect)? Justify your answer.
(d) Show the setup for the calculation of the percentage error in a students result if the student obtains a value
of 126 g mol1 for the molar mass of the solid when the actual value is 120. g mol1.
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-10-
2000 AP CHEMISTRY FREE-RESPONSE QUESTIONS
O3(g) + NO(g) O2(g) + NO2(g)
6. Consider the reaction represented above.
(a) Referring to the data in the table below, calculate the standard enthalpy change, H, for the reaction at
25C. Be sure to show your work.
O3(g)
Standard enthalpy of
formation, D H fo , at 25C
NO(g)
NO2(g)
143
90.
33
(kJ mol-1)
(b) Make a qualitative prediction about the magnitude of the standard entropy change, S, for the reaction at
25C. Justify your answer.
(c) On the basis of your answers to parts (a) and (b), predict the sign of the standard free-energy change, G,
for the reaction at 25C. Explain your reasoning.
(d) Use the information in the table below to write the rate-law expression for the reaction, and explain how you
obtained your answer.
Experiment
Number
Initial [O3]
(mol L1)
Initial [NO]
(mol L1)
1
2
3
4
0.0010
0.0010
0.0020
0.0020
0.0010
0.0020
0.0010
0.0020
Initial Rate of
Formation of NO2
(mol L1 s1)
x
2x
2x
4x
(e) The following three-step mechanism is proposed for the reaction. Identify the step that must be the slowest
in order for this mechanism to be consistent with the rate-law expression derived in part (d). Explain.
Step I:
O3 + NO O + NO3
Step II:
O + O3 2 O2
Step III:
NO3 + NO 2 NO2
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-11-
2000 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 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 (e.g., 1s2 2s2. . . etc.) for a selenium atom in the ground state.
Indicate the number of unpaired electrons in the ground-state 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 52).
(d) Selenium reacts with fluorine to form SeF4. Draw the complete Lewis electron-dot structure for SeF4 and
sketch the molecular structure. Indicate whether the molecule is polar or nonpolar, and justify your answer.
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-12-
2000 AP CHEMISTRY FREE-RESPONSE QUESTIONS
8. A volume of 30.0 mL of 0.10 M NH3(aq) is titrated with 0.20 M HCl(aq). The value of the base-dissociation
constant, Kb , for NH3 in water is 1.8 10-5 at 25C.
(a) Write the net-ionic equation for the reaction of NH3(aq) with HCl(aq).
(b) Using the axes provided below, sketch the titration curve that results when a total of 40.0 mL of
0.20 M HCl(aq) is added dropwise to the 30.0 mL volume of 0.10 M NH3(aq).
(c) From the table below, select the most appropriate indicator for the titration. Justify your choice.
Indicator
pKa
Methyl Red
5.5
Bromothymol Blue
7.1
Phenolphthalein
8.7
(d) If equal volumes of 0.10 M NH3(aq) and 0.10 M NH4Cl(aq) are mixed, is the resulting solution acidic,
neutral, or basic? Explain.
END OF EXAMINATION
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-13-