Download Practice Exam 3

Chem 106 Spring 2011 Hour Exam 3
Chap 19,20,Environ,22,23 Kotz 7th Ed
NAME____PRACTICE__________________________
Please take a seat in Row_____ Seat_____
Please:

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
Turn off and remove from your person all electronic items including PDAs, cell phones,
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devices. Place them in your purse or pack out of sight and hearing.

Place all papers, periodic tables, books, coat, hat, pack, or purse at the front or back of
the room, or on the floor.


All you need are #2 pencils & a non-programmable calculator.
After the exam begins, you may write in the exam booklet. Use the space to show work
for your own records.
Exam Directions
 This is a closed book, 90-minute exam. That means use nothing but the materials supplied to
answer the questions.
 There are a total of 12 pages in this exam, including the cover, back sheet, and scratch paper.
 The back sheet contains reference information including constants and periodic table.
 Write YOUR NAME on THIS PAGE NOW.
 Write YOUR NAME and your STUDENT NUMBER on the BUBBLE SHEET NOW.
 Your exam grading may be delayed or even prevented if the above items are missing or incorrect.
1
Multiple Choice (4 pts each)
Identify the choice that best completes the statement or answers the question. CAREFULLY fill in the correct answer on
the BUBBLE SHEET provided. Marks on this exam paper will NOT be graded, even if a mark here appears correct and
the answer on the bubble sheet is incorrect.
____
1. The second law of thermodynamics states that
a. in a spontaneous process, the entropy of the universe increases.
b. there is no disorder in a perfect crystal at 0 K.
c. the total energy of the universe is always increasing.
d. the total energy of the universe is constant.
e. mass and energy are conserved in all chemical reactions.
____
2. Which of the following C6H12 isomers is likely to have the lowest standard entropy in the liquid state?
a.
b.
c.
d.
e.
____
3. For which of the following reactions will the entropy of the system decrease?
a. 2 NH3(g)  N2(g) + 3 H2(g)
b. 2 C(s) + O2(g)  2 CO(g)
c. CaO(s) + CO2(g)  CaCO3(s)
d. N2O4(g)  2 NO2(g)
e. KOH(s)  K+(aq) + OH–(aq)
____
4. Hydrogen gas is a non-polluting fuel. Hydrogen gas may be prepared by electrolysis of water.
2 H2O( )  2 H2(g) + O2(g)
Predict the signs of rH and rS for the production of hydrogen gas by electrolysis of water.
a. rH > 0 and rS > 0
b. rH < 0 and rS > 0
c. rH > 0 and rS < 0
d. rH < 0 and rS < 0
e. rH = 0 and rS < 0
2
____
5. At what temperatures will a reaction be spontaneous if rH = –12.7 kJ and rS = +135 J/K?
a. All temperatures below 94.1 K
b. Temperatures between 12.7 K and 135 K
c. All temperatures above 94.1 K
d. The reaction will be spontaneous at any temperature.
e. The reaction will never be spontaneous.
____
6. Calculate rG for the reaction below at 25.0 C
CH4(g) + H2O(g)  3 H2(g) + CO(g)
a. –416.3 kJ
b. –142.2 kJ
c. +142.2 kJ
d. +315.0 kJ
e. +416.3 kJ
____
7. Assuming the following reaction proceeds in the forward direction,
2 Ni2+(aq) + Zn(s)  2 Ni(s) + Zn2+(aq)
a. Ni2+(aq) is the reducing agent and Zn(s) is the oxidizing agent.
b. Zn(s) is the reducing agent and Ni(s) is the oxidizing agent.
c. Ni2+(aq) is the reducing agent and Ni(s) is the oxidizing agent.
d. Zn(s) is the reducing agent and Zn2+(s) is the oxidizing agent.
e. Zn(s) is the reducing agent and Ni2+(s) is the oxidizing agent.
____
8. Write a balanced chemical equation for the following reaction in an acidic solution.
MnO4–(aq) + Fe(s)  Mn2+(aq) + Fe2+(aq)
a. 2 MnO4–(aq) + 5 Fe(s) + 16 H+(aq)  2 Mn2+(aq) + 5 Fe2+(aq) + 8 H2O( )
b. MnO4–(aq) + Fe(s) + 16 H+(aq)  Mn2+(aq) + Fe2+(aq) + 8 H2O( )
c. MnO4–(aq) + Fe(s)  Mn2+(aq) + Fe2+(aq) + 4 H2O( )
d. 2 MnO4–(aq) + Fe(s) + 16 H+(aq)  2 Mn2+(aq) + Fe2+(aq) + 8 H2O( )
e. MnO4–(aq) + 5 Fe(s) + 16 H+(aq)  Mn2+(aq) + 5 Fe2+(aq) + 8 H2O( )
____
9. What is the correct cell notation for a voltaic cell based on the reaction below?
Ag+(aq) + Sn(s)  Ag(s) + Sn2+(aq)
a. Ag(s) | Ag+(aq) || Sn2+(aq) | Sn(s)
b. Sn(s) || Sn2+(aq), Ag+(aq) | Ag(s)
c. Ag(s) || Ag+(aq), Sn2+(aq) || Sn(s)
d. Ag(s) | Sn2+(aq) || Ag+(aq) | Sn(s)
e. Sn(s) | Sn2+(aq) || Ag+(aq) | Ag(s)
3
____ 10. Which element or ion is the best oxidizing agent?
a.
b.
c.
d.
e.
I2(s)
Hg22+(aq)
I–(aq)
Ni2+(aq)
Hg( )
____ 11. Which of the following metals or metal ions will oxidize Fe(s)?
a.
b.
c.
d.
e.
Cu2+(aq) and Sn2+(aq)
Cu(s) and Sn(s)
Al3+(aq) and Mg2+(aq)
Al(s) and Mg(s)
Sn(s) and Al3+(aq)
____ 12. Given the following two half-reactions, write the overall balanced reaction in the direction in which it is
spontaneous and calculate the standard cell potential.
Cr3+(aq) + 3 e–  Cr(s)
Sn2+(aq) + 2 e–  Sn(s)
a. 2 Cr3+(aq) + 3 Sn(s)  2 Cr(s) + 3 Sn2+(aq)
b. 3 Cr3+(aq) + 2 Sn(s)  3 Cr(s) + 2 Sn2+(aq)
= +0.88 V
c. 2 Cr(s) + 3 Sn (aq)  2 Cr (aq) + 3 Sn(s)
d. 3 Cr(s) + 2 Sn2+(aq)  3 Cr3+(aq) + 2 Sn(s)
= +0.60 V
e. 2 Cr(s) + 3 Sn (aq)  2 Cr (aq) + 3 Sn(s)
= +1.00 V
2+
2+
= –1.94 V
3+
= –0.88 V
3+
____ 13. Calculate Ecell for the following electrochemical cell at 25 C
Pt(s) | Fe3+(aq, 0.25 M), Fe2+(aq, 0.25 M) || Cl–(aq, 0.20 M) | AgCl(s) | Ag(s).
a.
b.
c.
d.
e.
–0.590 V
–0.549 V
+0.508 V
–0.135 V
+0.549 V
Really, this cell notation should be
reversed to shown the Ag/AgCl
reaction (the oxidation) on the LEFT
as is common practice in the text.
____ 14. Which factor will increase the measured cell potential of the following galvanic cell?
Pt | Sn4+(aq, 1.0 M), Sn2+(aq, 1.0 M) || Cu2+(aq, 0.200 M) | Cu
a. switching from a platinum to a graphite anode
b. increasing the size of the anode
c. decreasing the concentration of Cu2+
d. increasing the concentration of Sn4+
e. decreasing the temperature of the cell
4
____ 15. Regarding the aurora borealis (“Northern Lights”), which of the following statements is (or are) true?
1. Green photons come from N2 molecules, and red photons come from O2 molecules.
2. Green photons are produced at very high altitudes, and red photons at lower altitudes.
3. Electrons from the Sun split N2 molecules, giving off intense UV radiation that creates O atoms in excited
states.
a.
b.
c.
d.
e.
1 only
1 and 2
2 only
1 and 3
3 only
____ 16. NO2 is the brown air pollutant molecule that is produced by high temperature N2 oxidation inside an internal
combustion engine. One resonance form of the molecule contains an unpaired electron plus how many single
bonds, double bonds, and lone-pairs, respectively?
a. 1, 1, 5
b. 2, 0, 6
c. 0, 2, 4
d. 1, 1, 6
e. 2, 0, 6
____ 17. Which of the following ions have an [Ar]3d6 electron configuration: Co2+, Fe2+, and Ni2+?
a. Co2+ only
b. Fe2+ only
c. Ni2+ only
d. Co2+ and Fe2+
e. Co2+ and Ni2+
____ 18. What element or compound is used to reduce Fe2O3 to Fe in a blast furnace?
a. H2(g)
b. Cl2(g)
c. C(s)
d. CaSiO3(s)
e. CO2(g)
____ 19. What is the coordination number of the central metal ion in [Fe(H2O)4(CN)2]Cl?
a. 2
b. 3
c. 4
d. 6
e. 7
5
____ 20. What is the name of the compound having the formula [Cr(en)2(NH3)2]Cl2?
a. dihydroxodiethlyenediamminechromate(II) chloride
b. diamminebis(ethylenediamine)chlorochromate(II)
c. bis(ethylenediamine)diamminechromium(II) dichloride
d. diamminebis(ethylenediamine)dichlorochromium(II)
e. diamminebis(ethylenediamine)chromium(II) chloride
____ 21. Which of the following reactions is an example of positron emission?
a.
b.
c.
d.
e.
____ 22. What nucleus decays by successive , , ,  emissions to produce uranium-236?
a.
b.
c.
d.
e.
____ 23. By what (single step) process does radon-222 decay to polonium-218?
a.  particle emission
b.  particle emission
c. positron emission
d. electron capture
e. neutron capture
____ 24. All of the following statements concerning nuclei are true EXCEPT
a. only hydrogen-1 and helium-3 have more protons than neutrons.
b. from He to Ca, stable nuclei have roughly equal numbers of protons and neutrons.
c. isotopes with a low neutron to proton ratio always decay by alpha particle emission.
d. the neutron to proton ratio in stable nuclei increases as mass increases.
e. beyond calcium, the neutron to proton ratio is always greater than one for stable nuclei.
____ 25. The half-life for the spontaneous decay of iodine-131 is 8.04 days. How much of a 0.50 g sample of this
isotope remains after 3.0 days?
a. 0.11 g
b. 0.13 g
c. 0.19 g
d. 0.28 g
e. 0.39 g
6
____ 26. Complete the following fission reaction.
a.
b.
c.
d.
e.
____ 27. What role do the cadmium control rods play in a fission reactor?
a. The rods control the rate of fission by absorbing neutrons.
b. The cadmium combines with spent uranium fuel to produce a non-radioactive product.
c. The rods focus the neutrons toward the center of the reactor.
d. The cadmium acts as a catalyst, enabling fission to occur at lower temperatures.
e. The rods move forward and backward, driving the pistons that turn the turbines.
SCRATCH PAPER
7
Name_____________________________________
Part II.
For full credit, you must show all conversion factors and the final answer with complete units, use the
correct number of significant figures, and round off correctly. WRITE CLEARLY: if the grader cannot read
your writing, no credit will be assigned.
28. (8 pts)
MgCO3(s)
Calculate the equilibrium constant for the following reaction at 25 °C.
MgO(s) + CO2(g)
29. (8 pts) Draw a realistic structural formula for a chiral coordination complex of say Ni2+ ion. For full
credit show all the atoms of the ligand groups.
8
30. (11 pts)
A sample of magnesium-28 is found to have an activity of 750 disintegrations per hour (dph). After 6.0 hours
the activity has decreased to 620 dph. What is the rate constant for the decay of magnesium-28?
9
May be removed – but please do not rip out the staple.
.
10
Half-Cell Reaction
–
–
F2(g) + 2 e  2 F (aq)
MnO4–(aq) + 8 H+(aq) + 5 e–  Mn2+(aq) + 4
H2O( )
Pd2+(aq) + 2 e–  Pd(s)
Ag+(aq) + e–  Ag(s)
Hg22+(aq) + 2 e–  2 Hg( )
Fe3+(aq) + e–  Fe2+(aq)
–
–
I2(s) + 2 e  2 I (aq)
Cu+(aq) + e–  Cu(s)
Cu2+(aq) + 2 e–  Cu(s)
Hg2Cl2(s) + 2 e–  2 Hg( ) + 2 Cl–(aq)
AgCl(s) + e–  Ag(s) + Cl–(aq)
2 H+(aq) + 2 e–  H2(g)
–
Pb (aq) + 2 e  Pb(s)
Sn2+(aq) + 2 e–  Sn(s)
Ni2+(aq) + 2 e–  Ni(s)
Co2+(aq) + 2 e–  Co(s)
PbSO4(s) + 2 e–  Pb(s) + SO42–(aq)
Cd2+(aq) + 2 e–  Cd(s)
2+
Cr3+(aq) + e–  Cr2+(aq)
Fe2+(aq) + 2 e–  Fe(s)
Cr3+(aq) + 3 e–  Cr(s)
Cr2+(aq) + 2 e–  Cr(s)
Mn2+(aq) + 2 e–  Mn(s)
Al3+(aq) + 3 e–  Al(s)
–
Mg (aq) + 2 e  Mg(s)
Na+(aq) + e–  Na(s)
2+
Eo (volts)
+2.87
+1.52
+0.900
+0.799
+0.789
+0.771
+0.535
+0.518
+0.337
+0.271
+0.222
0.000
–0.126
–0.140
–0.250
–0.280
–0.356
–0.40
–0.41
–0.44
–0.74
–0.91
–1.18
Substance
CH4(g)
C2H2(g)
C2H4(g)
C3H 8(g)
CCl4(l)
CCl4(g)
CH3OH(g)
Cl2(g)
CO(g)
CO2(g)
Fe(s)
Fe2O3(s)
Fe3O4(s)
H2O(g)
H2O(l)
H2(g)
MgCO3(s)
MgO(s)
O2(g)
P4O10(s)
H3PO4(l)
PbO(s)
Pb(s)
Si(s)
–1.66
–2.37
–2.71
11
 fH o
(kJ/mol)
-74.8
+226.7
+52.3
-103.8
-128.4
-96.0
-200.7
0.0
-110.5
-393.5
0.0
-825.5
-1118.4
-241.8
-285.8
0.0
-1095.8
-601.7
0.0
-2984.0
-1279.0
-217.3
0.0
0.0
 fG o
(kJ/mol)
-50.8
+209.2
+68.4
-23.5
-57.6
-53.6
-162.0
0.0
-137.2
-394.1
0.0
-742.2
-1015.4
-228.6
-237.1
0.0
-1028.3
-568.8
0.0
-2697.7
-1143.0
-187.9
0.0
0.0
S
(J/Kmol)
186.3
200.9
209.2
270.3
214.4
309.7
239.7
223.1
197.7
213.7
27.8
87.4
146.4
188.8
69.95
130.7
65.7
26.9
205.1
228.9
110.5
66.5
64.8
18.8
amount of substance
ABBREVIATIONS AND SYMBOLS
n
Faraday constant
F
molar
M
ampere
A
free energy
G
molar mass
M
atmosphere
atm
frequency

mole
mol
atomic mass unit
u
gas constant
R
Planck’s constant
h
atomic molar mass
A
gram
g
pressure
P
Avogadro constant
NA
hour
h
rate constant
k
Celsius temperature
°C
joule
J
reaction quotient
Q
centi- prefix
c
kelvin
K
second
s
coulomb
C
kilo- prefix
k
speed of light
c
electromotive force
E
liter
L
temperature, K
T
energy of activation
Ea
measure of pressure
mmHg
time
t
enthalpy
H
milli- prefix
m
volt
V
entropy
S
molal
m
volume
V
equilibrium constant
K
CONSTANTS
R = 8.314 J·mol-1·K-1
R = 0.0821 L·atm·mol-1·K-1
1 F = 96,500 C·mol-1
1 F = 96,500 J·V-1·mol-1
NA = 6.022 x 1023 mol-1
h = 6.626 x 10-34 J·s
c = 2.998 x 108 m·s-1
0 °C = 273.15 K
Arrhenius Equation
k  Ae
 Ea
E  Eo 
RT
Grahams Law of Effusion
rate A  M B 


rate B  M A 
EQUATIONS
Nernst Equation
1
2
RT
ln Q
nF
Nernst Equation at 25 °C
E  E0 
0.0592
log Q
n
12
Integrated Rate Laws
zero :
first :
A  A0  kt
ln A  ln A0  kt
second :
1
1
 kt 
A
A0