Download problem 8 on 2003B exam

AP® Chemistry
2003 Free-Response Questions
Form B
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2
Sr
87.62
56
Ba
Rb
85.47
55
Cs
*La
57
88.91
Y
39
Hf
72
91.22
Zr
40
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
Pr
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
58
Db
(262)
Rf
†Ac
105
(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
38
37
Ti
47.90
Fe
(244)
Pu
94
150.4
Sm
62
(265)
Hs
108
190.2
Os
76
101.1
Ru
44
55.85
Co
Ni
Pd
46
58.69
Cu
Ag
47
63.55
Cd
48
65.39
Zn
30
In
49
Sn
50
Sb
51
Te
52
I
53
Xe
54
Kr
83.80
Br
79.90
Se
78.96
As
74.92
36
Ge
Ga
69.72
35
35.453 39.948
72.59
32
31
Ar
18
34
32.06
30.974
28.09
26.98
Cl
17
33
S
P
16
Si
15
Al
14
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
29
Sc
44.96
28
Ca
27
40.08
26
K
25
39.10
24
20
19
23
24.30
22.99
22
21
Mg
Na
13
Ne
20.179
F
19.00
O
16.00
12
N
11
C
10.811 12.011 14.007
B
9.012
6.941
9
Be
8
Li
7
10
6
4
3
5
He
4.0026
2
H
PERIODIC TABLE OF THE ELEMENTS
1.0079
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.
STANDARD REDUCTION POTENTIALS IN AQUEOUS SOLUTION AT 25°C
E °( V )
Half-reaction
F2 ( g) + 2 e −
3+
Co
+ e−
3+
Au
→
e−
+3
e−
Cl 2 ( g) + 2
O 2 ( g) + 4 H
+
+4
e−
e−
Br 2 (l ) + 2
2 Hg 2 + + 2 e −
Hg
Ag
2+
+2
+
e−
Hg 2
Fe
+
2+
3+
e−
+2
e−
+ e−
I 2 (s) + 2 e −
+
Cu
+
2+
Cu
+
4+
Sn
e−
+2
2+
Cu
e−
e−
+2
S( s) + 2 H
Sn
Cr
2
1.07
→
Hg 2 2 +
0.92
→
Hg(l )
0.85
→
Ag( s)
0.80
→
2 Hg(l )
0.79
→
2+
Fe
−
0.77
→
2I
→
Cu( s)
0.52
→
Cu( s)
0.34
Cu
+
2+
0.53
0.15
→
Sn
→
H 2 S ( g)
0.14
0.00
0.15
Pb( s)
−0.13
+2
→
Sn( s)
−0.14
+2
e−
→
Ni( s)
−0.25
+2
e−
→
Co( s)
−0.28
→
Tl( s)
−0.34
→
Cd( s)
−0.40
2+
e−
+
2+
e−
+2
3+
+
e−
2+
3+
2+
Ca
Cr
−0.41
+ 2 e−
→
Fe( s)
−0.44
+ 3 e−
→
Cr( s)
−0.74
+ 2 e−
→
Zn( s)
−0.76
e−
+2
→
Mn( s)
−118
.
+3
e−
→
Al( s)
−1.66
+2
e−
→
Be( s)
−1.70
+2
e−
→
Mg( s)
−2.37
2+
2+
+
+
→
Na( s)
−2.71
→
Ca( s)
−2.87
+ 2 e−
→
Sr( s)
−2.89
+ 2 e−
→
Ba( s)
−2.90
→
Rb( s)
−2.92
+ e−
→
K(ss)
−2.92
+
e−
→
Cs( s)
−2.92
+
e−
→
Li( s)
−3.05
+2
2+
Rb
+
+
+
+
e−
e−
2+
2+
Ba
→
2+
2+
3+
Na
Li
→
→
Mg
Cs
+2
e−
1.23
Br −
e−
Be
K
2 H 2 O(l )
+ 2 e−
Mn
Sr
→
1.36
2+
Zn
Al
2 Cl
1.50
H 2 ( g)
Cd
Fe
→
−
→
+
Cr
Au( s)
+ 2 e−
Co
Tl
→
1.82
2+
2+
Ni
Co
2.87
+
2H
Pb
+
2+
→
→
e−
2 F−
+ e−
3
ADVANCED PLACEMENT CHEMISTRY EQUATIONS AND CONSTANTS
ATOMIC STRUCTURE
D E = hv
c = lv
=
=
=
=
u =
n =
m =
E
v
l
p
l = mhu
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 ]
Planck’s constant, h = 6.63 × 10 −34 J s
Boltzmann’s constant, k = 1.38 × 10 −23 J K −1
[OH − ] [ HB + ]
Kb =
[ B]
Avogadro’s 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
1 electron volt per atom = 96.5 kJ mol −1
pH = − log [ H + ], pOH = − log [OH − ]
14 = pH + pOH
pH = pKa + log
[A − ]
[ HA ]
Equilibrium Constants
+
[HB ]
[ B]
pKa = − log Ka , pKb = − log Kb
pOH = pKb + log
K p = Kc ( RT )
energy
frequency
wavelength
momentum
velocity
principal quantum number
mass
Dn
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
H o = standard enthalpy
THERMOCHEMISTRY
DH o
DG o
G o = standard free energy
∑
∑
o
= ∑ DHf products − ∑ DH fo reactants
= ∑ DGfo products − ∑ DGfo reactants
DS o =
S o products −
S o reactants
Eo
T
n
m
q
c
Cp
DG o = DH o − TD S o
= − RT ln K = −2.303 RT log K
= −n Ᏺ E o
=
=
=
=
=
=
=
standard reduction potential
temperature
moles
mass
heat
specific heat capacity
molar heat capacity at constant pressure
1 faraday Ᏺ = 96,500 coulombs
DG = DG o + RT ln Q = DG o + 2.303 RT log Q
q = mcDT
DH
Cp =
DT
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
= 2 2
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
molarity, M = moles solute per liter solution
molality = moles solute per kilogram solvent
DT f = iK f ™ molality
=
=
=
=
=
=
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
van’t Hoff factor
molal freezing-point depression constant
Kb
Q
I
q
t
=
=
=
=
=
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
Gas constant, R = 8.31 J mol -1 K -1
V
= 0.0821 L atm mol -1 K -1
= 8.31 volt coulomb mol -1 K -1
Boltzmann’s constant, k = 1.38 ™ 10 -23 J K -1
OXIDATION-REDUCTION; ELECTROCHEMISTRY
K f for H 2 O = 1.86 K kg mol -1
c
Q =
[C ] [ D ]
d
a
b
K b for H 2 O = 0.512 K kg mol -1
, where a A + b B → c C + d D
[ A ] [ B]
q
I =
t
o − RT ln Q = E o − 0.0592 log Q @ 25o C
E cell = E cell
cell
nᏲ
n
log K =
nE o
0.0592
1 atm = 760 mm Hg
= 760 torr
STP = 0.000 o C and 1.000 atm
Faraday’s constant, Ᏺ = 96,500 coulombs per mole
of electrons
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5
2003 AP® CHEMISTY 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 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
goldenrod cover. Do NOT write your answers on the lavender insert.
Answer Question 1 below. The Section II score weighting for this question is 20 percent.
→ H (g) + I (g)
2 HI(g) ←
2
2
1. After a 1.0 mole sample of HI(g) is placed into an evacuated 1.0 L container at 700. K, the reaction represented
above occurs. The concentration of HI(g) as a function of time is shown below.
(a) Write the expression for the equilibrium constant, Kc , for the reaction.
(b) What is [HI] at equilibrium?
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6
2003 AP® CHEMISTY FREE-RESPONSE QUESTIONS (Form B)
(c) Determine the equilibrium concentrations of H2(g) and I2(g).
(d) On the graph above, make a sketch that shows how the concentration of H2(g) changes as a function
of time.
(e) Calculate the value of the following equilibrium constants at 700. K.
(i) Kc
(ii) Kp
(f) At 1,000 K, the value of Kc for the reaction is 2.6 ™ 10 – 2. In an experiment, 0.75 mole of HI(g),
0.10 mole of H2(g), and 0.50 mole of I2(g) are placed in a 1.0 L container and allowed to reach
equilibrium at 1,000 K. Determine whether the equilibrium concentration of HI(g) will be greater than,
equal to, or less than the initial concentration of HI(g). Justify your answer.
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7
2003 AP® CHEMISTY FREE-RESPONSE QUESTIONS (Form B)
Answer EITHER Question 2 below OR Question 3 printed on page 9. 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 chemical reactions.
(a) Iron(III) oxide can be reduced with carbon monoxide according to the following equation.
Fe2O3(s) + 3 CO(g) “ 2 Fe(s) + 3 CO2(g)
A 16.2 L sample of CO(g) at 1.50 atm and 200.•C is combined with 15.39 g of Fe2O3(s).
(i) How many moles of CO(g) are available for the reaction?
(ii) What is the limiting reactant for the reaction? Justify your answer with calculations.
(iii) How many moles of Fe(s) are formed in the reaction?
(b) In a reaction vessel, 0.600 mol of Ba(NO3)2(s) and 0.300 mol of H3PO4(aq) are combined with deionized
water to a final volume of 2.00 L. The reaction represented below occurs.
3 Ba(NO3)2(aq) + 2 H3PO4(aq) “ Ba3(PO4)2(s) + 6 HNO3(aq)
(i) Calculate the mass of Ba3(PO4)2(s) formed.
(ii) Calculate the pH of the resulting solution.
(iii) What is the concentration, in mol L–1, of the nitrate ion, NO3– (aq), after the reaction reaches
completion?
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students and parents at www.collegeboard.com/apstudents.
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8
2003 AP® CHEMISTY FREE-RESPONSE QUESTIONS (Form B)
3. In an experiment, a sample of an unknown, pure gaseous hydrocarbon was analyzed. Results showed that the
sample contained 6.000 g of carbon and 1.344 g of hydrogen.
(a) Determine the empirical formula of the hydrocarbon.
(b) The density of the hydrocarbon at 25•C and 1.09 atm is 1.96 g L–1.
(i) Calculate the molar mass of the hydrocarbon.
(ii) Determine the molecular formula of the hydrocarbon.
In another experiment, liquid heptane, C7H16(l), is completely combusted to produce CO2(g) and H2O(l), as
represented by the following equation.
C7H16(l) + 11 O2(g) “ 7 CO2(g) + 8 H2O(l)
The heat of combustion,
o
DH comb
, for one mole of C7H16(l) is -4.85 ™ 103 kJ.
(c) Using the information in the table below, calculate the value of
DH fo for C7H16(l) in kJ mol – 1.
Compound
DH fo (kJ mol – 1)
CO2(g)
H2O(l)
–393.5
–285.8
(d) A 0.0108 mol sample of C7H16(l) is combusted in a bomb calorimeter.
(i) Calculate the amount of heat released to the calorimeter.
(ii) Given that the total heat capacity of the calorimeter is 9.273 kJ •C –1, calculate the temperature change
of the calorimeter.
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9
2003 AP® CHEMISTY 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 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) Hot hydrogen gas is passed over heated copper(II) oxide solid.
(b) Solid sodium hydride is added to water.
(c) Propanone is burned in air.
(d) A solution of lead(II) nitrate is added to a solution of potassium sulfate.
(e) Ammonia gas is mixed with hydrogen chloride gas.
(f) Sulfur trioxide gas is bubbled into water.
(g) Excess concentrated potassium hydroxide solution is added to a solution of nickel(II) chloride.
(h) Solid sodium acetate is added to 1.0 M hydrobromic acid.
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10
2003 AP® CHEMISTY FREE-RESPONSE QUESTIONS (Form B)
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 12. Both of these questions will be graded. The
Section II score weighting for these questions is 30 percent (15 percent each).
5. Oxalic acid, H2C2O4 , is a primary standard used to determine the concentration of potassium permanganate,
KMnO4 , in solution. The equation for the reaction is as follows.
2 KMnO4(aq) + 5 H2C2O4(aq) + 3 H2SO4(aq) “ 2 MnSO4(aq) + 10 CO2(g) + 8 H2O(l) + K2SO4(aq)
A student dissolves a sample of oxalic acid in a flask with 30 mL of water and 2.00 mL of 3.00 M H2SO4 . The
KMnO4 solution of unknown concentration is in a 25.0 mL buret. In the titration, the KMnO4 solution is added
to the solution containing oxalic acid.
(a) What chemical species is being oxidized in the reaction?
(b) What substance indicates the observable endpoint of the titration? Describe the observation that shows the
endpoint has been reached.
(c) What data must be collected in the titration in order to determine the molar concentration of the unknown
KMnO4 solution?
(d) Without doing any calculations, explain how to determine the molarity of the unknown KMnO4 solution.
(e) How would the calculated concentration of the KMnO4 solution be affected if 40 mL of water was added to
the oxalic acid initially instead of 30 mL? Explain your reasoning.
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11
2003 AP® CHEMISTY FREE-RESPONSE QUESTIONS (Form B)
6. Answer the following questions about electrochemistry.
(a) Several different electrochemical cells can be constructed using the materials shown below. Write the
balanced net-ionic equation for the reaction that occurs in the cell that would have the greatest positive
o
.
value of E cell
o
(b) Calculate the standard cell potential, E cell
, for the reaction written in part (a).
(c) A cell is constructed based on the reaction in part (a) above. Label the metal used for the anode on the cell
shown in the figure below.
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12
2003 AP® CHEMISTY FREE-RESPONSE QUESTIONS (Form B)
(d) Of the compounds NaOH, CuS, and NaNO3 , which one is appropriate to use in a salt bridge? Briefly
explain your answer, and for each of the other compounds, include a reason why it is not appropriate.
(e) Another standard cell is based on the following reaction.
Zn + Pb2+ “ Zn2+ + Pb
If the concentration of Zn2+ is decreased from 1.0 M to 0.25 M, what effect does this have on the cell
potential? Justify your answer.
Answer EITHER Question 7 below OR Question 8 printed on page 14. 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. Account for the following observations using principles of atomic structure and/or chemical bonding. In each
part, your answer must include specific information about both substances.
(a) The Ca2+ and Cl– ions are isoelectronic, but their radii are not the same. Which ion has the larger radius?
Explain.
(b) Carbon and lead are in the same group of elements, but carbon is classified as a nonmetal and lead is
classified as a metal.
(c) Compounds containing Kr have been synthesized, but there are no known compounds that contain He .
(d) The first ionization energy of Be is 900 kJ mol –1, but the first ionization energy of B is 800 kJ mol –1.
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13
2003 AP® CHEMISTY FREE-RESPONSE QUESTIONS (Form B)
8. The decay of the radioisotope I-131 was studied in a laboratory. I-131 is known to decay by beta ( -01 e ) emission.
(a) Write a balanced nuclear equation for the decay of I-131.
(b) What is the source of the beta particle emitted from the nucleus?
The radioactivity of a sample of I-131 was measured. The data collected are plotted on the graph below.
(c) Determine the half-life, t1/2 , of I-131 using the graph above.
(d) The data can be used to show that the decay of I-131 is a first-order reaction, as indicated on the graph
below.
(i) Label the vertical axis of the graph above.
(ii) What are the units of the rate constant, k, for the decay reaction?
(iii) Explain how the half-life of I-131 can be calculated using the slope of the line plotted on the graph.
(e) Compare the value of the half-life of I-131 at 25•C to its value at 50•C.
END OF EXAMINATION
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