1. [7 points] Which element is oxidized in the reaction below?
K2CrO4 (aq) + BaCl2 (aq) → BaCrO4 (s) + 2KCl
a.
b.
c.
d.
e.
Cl
Cr
O
Ba
This is not an oxidation-reduction reaction
2. [7 points] What are the coefficients of Cl2O7 and H2O, when the following redox
equation is balanced in basic solution?
H2O2 + Cl2O7 → ClO2- + O2 + H2O
a.
b.
c.
d.
e.
1, 1
2, 7
1, 5
1, 3
None of the above
3. [7 points] What is the coefficient of the hypochlorite ion, ClO-, when the
following equation is balanced in basic solution?
ClO- + S2O32- → Cl- + SO42a.
b.
c.
d.
e.
4.
1
2
3
4
5
[7 points] The purpose of a salt bridge in an electrochemical cell is to ______ .
a.
b.
c.
d.
e.
Maintain electrical neutrality in the half-cells via migration of ions.
Provide a source of ions to react at the anode and cathode
Provide oxygen to facilitate oxidation at the anode
Provide a means for electrons to travel from the anode to the cathode
Provide a means for electrons to travel from the cathode to the anode
5. [7 points] In experiment 25 you added an iron nail to a solution containing tin
ions in order to reduce Sn4+ ions to Sn2+. In this reaction Fe (s) acts as a
reducing agent. Which of the following reagents could be used as an alternative
reducing agent, to drive a spontaneous redox reaction (consider the standard
reduction potentials found on the back page to answer this question)?
(i) FeCl2 (aq)
a.
b.
c.
d.
e.
(ii) AgNO3 (aq)
(iii) H2 (g)
(iv) Cu (s)
FeCl2 (aq)
H2 (g)
AgNO3 (aq)
AgNO3 (aq) & H2 (g)
Cu (s) & FeCl2 (aq)
6. [7 points] Consider a voltaic cell where one cell compartment contains Cu(NO3)2
(aq) in contact with a Cu electrode, while the other cell compartment contains
CrCl3 (aq) in contact with a Cr electrode. Which electrode is the anode and what
is the standard cell potential (Eºcell) for this cell?
a. Anode = Copper, Eºcell = +0.40 V
b. Anode = Chromium, Eºcell = +0.40 V
c. Anode = Copper, Eºcell = +1.08 V
d. Anode = Chromium, Eºcell = +1.08 V
e. Anode = Copper, Eºcell = -1.08 V
7. [7 points] In the above problem what would be the cell potential if the
temperature were 298 K, the CrCl3 concentration was 0.50 M, and the Cu(NO3)2
concentration was 0.0025 M?
a.
b.
c.
d.
e.
+0.47 V
+1.51 V
+1.15 V
+1.01 V
None of the above
8. [7 points] Consider a voltaic cell based on the following reaction:
2H+ (aq) + Sn (s) → Sn2+ (aq) + H2 (g)
Which of the following actions would increase the measured cell potential?
a.
b.
c.
d.
e.
Increasing the pH in the cathode compartment
Increasing the pressure of H2 gas in the cathode compartment
Increasing the size of the tin anode
Decreasing [Sn2+] in the anode compartment
All of the above actions will increase the cell potential
9. [7 points] What is the value of ΔGº for this reaction (standard reduction
potentials are given on the last page)?
3Sn4+ (aq) + 2Cr (s) → 2Cr3+ (aq) + 3Sn2+ (aq)
a.
b.
c.
d.
e.
–342 kJ
+515 kJ
–515 kJ
+85.8 kJ
–85.8 kJ
10. [7 points] What is the anode in an alkaline battery?
a.
b.
c.
d.
e.
MnO2
KOH
Zn powder
Mn2O3
Pt
11. [7 points] How many seconds are required to produce 4.00 g of aluminum metal
from the electrolysis of molten AlCl3 with an electrical current of 12.0 A.
a.
b.
c.
d.
e.
27.0 s
9.00 s
1.19 × 103 s
2.90 × 105 s
3.57 × 103 s
12. [7 points] Calculate the equilibrium constant at 25 ºC for the following reaction:
Fe2+ (aq) + Ag+ (aq) → Ag (s) + Fe3+ (aq)
a.
b.
c.
d.
e.
0.51
3.2
3.3 × 1026
0.31
None of the above
Construct a molecular orbital diagram for carbon monoxides, CO, and use it to
answer the following three questions:
13. [7 points] How would you describe the highest occupied molecular orbital
(HOMO) and lowest unoccupied molecular orbital (LUMO):
a.
b.
c.
d.
e.
HOMO
HOMO
HOMO
HOMO
HOMO
=
=
=
=
=
pi bonding, LUMO = sigma antibonding
pi antibonding, LUMO = sigma antibonding
pi bonding, LUMO = pi antibonding
sigma antibonding, LUMO = pi antibonding
sigma bonding, LUMO = pi bonding
14. [7 points] What is the bond order in CO?
a.
b.
c.
d.
e.
1
1.5
2
2.5
3
15. [7 points] If you were to stretch the C-O bond, so that the C-O bond distance
increases, how would that impact the HOMO-LUMO energy gap?
a.
b.
c.
d.
It would increase
It would decrease
It would remain unchanged
It is impossible to know from the information given
16. [7 points] Complexes containing transition metals with which one of the following
electron configurations are usually colorless?
(a) d2
(b) d1
(c) d5
(d) d8
(e) d10
17. [7 points] Which of the following MO’s represents an antibonding pi (π*)
interaction?
(a)
(c)
(b)
(d)
18. [7 points] Given the fact that [Cr(H2O)6]3+ is violet, which of the following
complex ions is most likely to be green?
a.
b.
c.
d.
[Cr(NO2)6]3[CrCl6]3[Cr(NH3)6]3+
[Cr(CN)6]3-
19. [7 points] The permanganate ion, MnO4-, is purple with an absorption maximum at
565 nm, while the CrO42- ion is yellow with an absorption maximum near 400 nm.
What color would you expect for the hypothetical FeO4 molecule.
a.
b.
c.
d.
e.
Red
Green
Blue
Orange
Colorless, because the oxygen to iron charge transfer transition would
fall in the UV region of the spectrum.
20. [7 points] What electronic transition is responsible for the blue color of a
sapphire?
a. A d to d transition on a chromium impurity
b. A charge transfer from oxygen to aluminum
c. A charge transfer transition from oxygen to a d-orbital on a chromium
impurity
d. A charge transfer from a Fe2+ ion impurity to a neighboring Ti4+ ion
impurity
e. A d to d transition on a cobalt impurity
21. [7 points] How many unpaired electrons are there on a [NiCl4]2- complex ion with
tetrahedral geometry?
a.
b.
c.
d.
e.
0
1
2
4
8
22. [7 points] What structure can be described as a cubic close packing of anions
with 50% of the tetrahedral holes filled?
a.
b.
c.
d.
e.
Rock salt
Nickel Arsenide
Zinc Blende
Wurtzite
Cesium Chloride
23. [7 points] The mineral cinnabar (HgS) adopts the Zinc Blende structure type
with a unit cell edge of 5.852 Å? What is the coordination environment of
mercury and of sulfur.
a.
b.
c.
d.
e.
Hg →
Hg →
Hg →
Hg →
Hg →
octahedron, S → octahedron
tetrahedron, S → cube
tetrahedron, S → tetrahedron
tetrahedron, S → octahedron
octahedron, S → tetrahedron
24. [7 points] Given the information in the previous problem what is the Hg-S bond
distance in cinnabar (HgS).
a.
b.
c.
d.
e.
2.93
2.53
4.39
5.07
2.27
Å
Å
Å
Å
Å
25. [7 points] The strongest peak in the X-ray diffraction pattern of cubic MgO,
which adopts the rock salt structure type, is the (111) peak. If the pattern was
collected with Cu Ka radiation (wavelength of 1.541 Å), and the 2-theta location
of the (111) peak is 37.0º, what is the length of the unit cell edge, a ?
a.
b.
c.
d.
e.
2.22 Å
4.21 Å
2.43 Å
5.06 Å
None of the above
Standard Reduction Potentials
Half Reaction
Eº (V)
Cr3+ (aq) + 3e- → Cr (s)
-0.74
Ag+ (aq) + e- → Ag (s)
+0.80
Fe2+ (aq) + 2e- → Fe (s)
-0.44
Fe3+ (aq) + e- → Fe2+ (s)
+0.77
Cu2+ (aq) + 2e- → Cu (s)
+0.34
Zn2+ (aq) + 2e- → Zn (s)
-0.76
Pb2+ (aq) + 2e- → Pb (s)
-0.13
Sn4+ (aq) + 2e- → Sn2+ (aq)
+0.15
Sn2+ (aq) + 2e- → Sn (s)
-0.14
2H+ (aq) + 2e- → H2 (g)
+0.00
BiO+ (aq) + 2H+ (aq) + 3 e- → Bi (s) + H2O
+0.32
Spectrochemical Series
Weak Field
Ligands
Cl- < F- < H2O < NH3 < NO2- < CN-
Physical Constants & Conversion Factors
h = 6.626 × 10-34 J-s
c = 2.998 × 108 m/s
R = 8.314 J/K-mol
1 Å = 1 × 10-10 m
1 eV = 1.602 × 10-19 J
1 F = 96,500 C/mol = 96,500 J/V-mol
1 A = 1 C/s
1 eV = 1.602 × 10-19 J
Strong Field
Ligands