Chemistry 105 B
Exam 3
First Letter of
last Name
PLEASE PRINT YOUR NAME IN BLOCK LETTERS
Name: __________________________________
04/02/09
Last 4 Digits of USC ID:____ ____ ____ ____
Dr. Jessica Parr
Lab TA’s Name: _________________________________
Question
1
2
3
4
5
6
7
8
Points
18
8
10
20
10
10
14
10
Total
100
Score
Grader
Please Sign Below:
I certify that I have observed all the rules of Academic Integrity while taking this examination.
Signature: _______________________________________________________________
Instructions:
1. You must show work to receive credit.
2. If necessary, please continue your solutions on the back of the preceding page (facing you).
3. YOU MUST use black or blue ink. (No pencil, no whiteout, no erasable ink.)
4. There are 8 problems on 11 pages. Please count them before you begin. A periodic table and
some useful equations can be found on the last page.
5. Good luck!! =)
1
1. (18 pt) Determine whether the following statements are true or false. If false, correct the bold
part of the statement to make the statement correct.
a. The third law of thermodynamics states that the entropy of a perfect crystal at 0 K is zero.
True
False
b. When a process is spontaneous it has a rate constant greater than 1 for the direction written.
True
False
c. All standard reduction potentials are measured relative to the standard water electrode.
True
False
d. In the redox reaction: 2MnO4-(aq) + 6H+ (aq) + 5ClO3- (aq) Æ 2Mn2+ (aq) + 3H2O (l) + 5ClO4- (aq),
five electrons are transferred.
True
False
True
False
e. Carbon dating can be used to date all types of material.
f. The binding energy for a nucleus is the energy required to break a nucleus into its component
nucleons.
True
False
2
2. (8 pt) For mercury, the enthalpy of vaporization is 58.51 kJ/mol and the entropy of
vaporization is 92.92 J/K*mol. What is the normal boiling point of mercury?
3
3. (10 pt) The Kb for methylamine (CH3NH2) at 25oC is 4.4 x 10-4. What is the value of ΔG
when [OH-] = 1.5 x 10-8 M, [CH3NH3+] = 5.5 x 10-4 M, and [CH3NH2] = 0.120 M?
Will the reaction proceed toward the products or the reactants? Why?
4
4. (20 pt) A galvanic cell is based on the following reduction reactions:
Co3+ (aq) + e- Æ Co2+ (aq)
εo = 1.82 V
Cr2O72- (aq) + 14 H+ (aq) + 6e- Æ 2 Cr3+ (aq) + 7 H2O (l)
εo = 1.33 V
a. What is the balanced reaction for this cell?
b. What is the standard cell potential for this cell?
c. Give the line notation for this cell.
d. In a galvanic cell, what is the purpose of the porous disk or salt bridge?
e. If the cell is at standard conditions what are the concentrations of the ions in solution?
5
f. On the figure below add in the following for the galvanic cell described above:
i. The ions in solution in each compartment
ii. Label the cathode and anode compartments
iii. Label the composition of the electrodes
iv. Indicate the direction of electron flow
porous
disk
6
5. (10 pt) A voltaic cell is constructed that uses the following half-cell reactions:
Cu+ (aq) + e- Æ Cu (s)
εo = 0.521 V
I2 (s) + 2 e- Æ 2 I- (aq)
εo = 0.536 V
The cell is operated at 298 K with [Cu+] = 0.25 M and [I-] = 3.5 M.
a. What is the cell potential for this voltaic cell, at these non-standard conditions?
b. What is being oxidized at the anode, with these non-standard conditions?
c. If the [Cu+] was equal to 1.50 M, at what concentration of I- would the cell potential be zero?
7
6. (10 pt) An aqueous solution of an unknown salt of manganese and chloride is electrolyzed for
1.35 hr with a current of 3.21 A. If 2.22 g of Mn metal is produced at the cathode, what is the
formula for the manganese chloride salt?
8
7. (14 pt)
a. Write the equation for the decay of 241Am by alpha-particle production.
b. 241Am decays by a series of alpha-particle and beta-particle productions, taking 241Am through
many transformations to get to 209Bi. In the complete decay series, how many alpha particles
and beta particles are produced?
_________ alpha-particles
___________ beta-particles
c. 241Am has a half-life of 432.2 years. How long will it take for a 0.450 g sample to decay to
18.5 % of its original mass?
9
8. (10 pt) The binding energy per nucleon for 27Mg is 1.326 x 10-12 J/nucleon. Determine the
atomic mass of 27Mg in amu.
Proton Mass
1.00728 amu
Neutron Mass
1.00866 amu
Electron Mass
5.48580 x 10-4 amu
10
I
VIII
1
H
1.008
3
Li
6.941
11
Na
22.99
19
K
39.10
II
III
IV
V
VI
VII
4
Be
9.012
12
Mg
24.31
20
Ca
40.08
21
Sc
44.969
22
Ti
47.88
23
V
50.94
24
Cr
51.996
25
Mn
54.9380
26
Fe
55.847
27
Co
58.9332
28
Ni
58.69
29
Cu
63.546
30
Zn
65.377
5
B
10.81
13
Al
26.98
31
Ga
69.72
6
C
12.01
14
Si
28.09
32
Ge
72.59
7
N
14.01
15
P
30.97
33
As
74.9216
8
O
16.0
16
S
32.07
34
Se
78.96
9
F
19.00
17
Cl
35.45
35
Br
79.90
2
He
4.003
10
Ne
20.18
18
Ar
39.95
36
Kr
83.80
37
Rb
85.47
55
Cs
132.9
87
Fr
(223)
38
Sr
87.62
56
Ba
137.3
88
Ra
226.0
39
Y
88.91
57
La
138.9
89
Ac
227.0
40
Zr
91.22
72
Hf
178.5
104
Rf
261)
41
Nb
92.91
73
Ta
180.9
105
Db
(262)
42
Mo
95.94
74
W
183.85
106
Sg
(263)
43
Tc
(99)
75
Re
186.2
107
Bh
(262)
44
Ru
101.1
76
Os
190.2
108
Hs
(265)
45
Rh
102.9
77
Ir
192.2
109
Mt
(268)
46
Pd
106.4
78
Pt
195.09
110
Ds
(271)
47
Ag
107.9
79
Au
197.0
111
Rg
(272)
48
Cd
112.4
80
Hg
200.6
112
Uub
49
In
114.8
81
Tl
204.4
113
Uut
50
Sn
118.7
82
Pb
207.2
114
Uuq
51
Sb
121.8
83
Bi
209.0
115
Uup
52
Te
127.6
84
Po
(209)
53
I
126.9
85
At
(210)
54
Xe
131.3
86
Rn
(222)
58
Ce
140.1
90
Th
232.0
59
Pr
140.9
91
Pa
231.0
63
Eu
151.96
95
Am
(243)
64
Gd
157.3
96
Cm
(247)
Lanthanides
Actinides
60
Nd
144.2
92
U
238.0
61
Pm
(145)
93
Np
237.0
62
Sm
150.4
94
Pu
(244)
65
Tb
158.9
97
Bk
(247)
66
Dy
162
98
Cf
(251)
67
Ho
164.9
99
Es
(252)
68
Er
167.3
100
Fm
(257)
69
Tm
168.9
101
Md
(258)
70
Yb
173.0
102
No
(259)
Useful Equations and Constants:
F = 96,485 C/mol e-
ΔGo = -RT ln(K)
R = 8.314 J/K*mol = 0.08206 L*atm/K*mol
ΔGo = ΔHo - TΔSo
ΔSsurr = -ΔH/T
ΔSuniv = ΔSsys + ΔSsurr
ΔG = ΔGo + RT ln(Q)
NA = 6.022 x 1023
ε = εo – (RT/nF)lnQ
ε = εo – (0.0591/n)logQ
ΔG = -nFε
ΔE = mc2
c = 3.00 x 108 m/s
1 amu = 1.6605 x 10-27 kg
1A = 1C/s
1 MeV = 1.60 x 10-13 J
ln[ A] = −kt + ln[ A]0
t1 / 2 =
0.693
k
Rate = k[A]
11
71
Lu
175
103
Lr
(26)