CHEMISTRY 362
Descriptive Inorganic Chemistry
M. Y. Darensbourg
Examination III
April 19, 2017
Name: ___________________________________
An Aggie does not lie, cheat or steal or tolerate (and BTHO)
those who do.
Signed: ___________________________________________
Point Group Assignment
S = Σms
Spin multiplicity = 2S + 1
𝜇𝑠.𝑜. = 2�𝑆 (𝑆 + 1)
CHEMISTRY 362
Descriptive Inorganic Chemistry
M. Y. Darensbourg
Examination III
April 19, 2017
Question
Points possible
I
35
II
15
III
30
IV
35
Total
115
Points received
This Exam requires you to combine knowledge from many of the topics covered
in this course and to apply the concepts and principles that are in your inorganic
chemistry knowledge base. You can do this. Can you believe we are at the
third examination?
I. 35 pts. This question relates to the similarities between main group, non-metal oxides
and transition metal oxides. Fill in the blanks in paragraphs as indicated. You might find
some of the answers in these formula and words:
SO 3 ; SO 2 ; V 2 O 5 ; VO 2 ; acidic; basic; reducing agent; oxidizing agent;
redox reaction; neutralization; C 2 , C 3 , C 4 .
A) The oxide of vanadium in its highest oxidation state,______, reacts with a sulfoxy
species,_______, and forms the one-electron reduced vanadium oxide, ______ , and a
different sulfoxy species, _________. The balanced chemical equation describing this
____________ reaction is give below and the oxidation states of vanadium and of sulfur
in each compound are listed below each compound in the equation.
____________
+ ____________
ox. states: ______
______
____________
+ ____________
______
______
The vanadium oxide that is paramagnetic, ________, has______ unpaired electron(s)
and the ground state term symbol for vanadium in this oxide is ________. The
vanadium oxide that is diamagnetic, ______, has_____ unpaired electron(s) and a spin
multiplicity of ____.
Its ground state term symbol is_____.
B) Both oxides of sulfur dissolve in water to give acids. Complete the equations describing
these reactions, and suggest pKa values of each according to Pauling’s rule:
pK a1
SO 2
+ H2O
____________
__________
SO 3
+ H2O
____________
__________
From these values we conclude that ________ is the stronger acid.
Page 1 of 5
C) Give the Lewis structures and sketch the VSEPR-predicted geometries of SO 2 and SO 3 .
SO 2
SO 3
D) The principal rotation axis for SO 2 is _______ and for SO 3 is __________.
The point group assignment for SO 2 is _______ and for SO 3 is __________.
E) Give at least two resonance structures for SO 2 and use formal charge criteria to select
the “best” structure.
F) The hybrid orbitals on S that are used for the S-O sigma bond overlap in SO 3 are
_____.
G) Sketch the orbital overlap that defines one π-bond in SO 3 .
II. 15 pts a) Reported in 2015 in the journal of Physical Chemistry was an experimental
and computational study of the interaction of
ammonia and SO 3 . A graphic in that paper is
shown to the right. Label the type of bond or
interaction between S and O at 1.450Å; between N
and S at 1.975Å; and between N and H at 1.862Å.
Terms you might consider using are: H-bonding,
dipole-dipole interaction; Lewis acid/base
interaction; ionic bonding; covalent bond, etc.
b) Neglecting the second NH 3 molecule, what is the principal rotation axis and the
symmetry point group of the SO 3 -NH 3 adduct?
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III. 30 pts.
A) Due to their ability to exist in various oxidation states, transition metals typically form
multiple types of oxides. Give the oxidation states of Fe and Cu and the d-electron
count with each in the following oxides.
Oxides
Oxidation State(s) of M
d-electron count of Fe or Cu
FeO
Fe 2 O 3
Fe 3 O 4
[FeO 4 ]2Cu 2 O
CuO
Cu 2 O 3
B) These oxides result from complete 4-electron reduction of O 2 , yielding O2− anions.
However, partial or incomplete one-electron reduction of O 2 yields O 2 −, a molecular
anion. Give the MO assignment (KKσ 2s 2σ* 2s . . .) of O 2 and O 2 −, and for each give
the bond order and spin-only magnetic moment.
B.O.
µ so
O2
__________________________________________
O2−
__________________________________________
________
________
_______
_______
C) Copper forms a compound of formula CuO 2 , similarly to ZnO 2 , while ZnO 2 is
colorless and diamagnetic, CuO 2 is a dark olive green and has 𝜇𝑠.𝑜. = 1.73 𝐵𝐵. As Zn
can only have oxidation state of zero, Zn0 (as in the metal) or 2+ (as in Zn2+), predict
the electronic structure (Lewis structure) of the oxygen species in ZnO 2 and CuO 2 , and
give the oxidation state of Cu in this compound.
D) The unit cell of one of the copper oxides is given here.
What is the formula of this copper oxide? How did you arrive
at your answer?
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IV. 35 pts
A) For the electrochemical cell at right,
a) Identify the cathode and anode, and give the half reactions
that occur at the cathode and anode, respectively.
b) Indicate the direction of electron flow in the external circuit.
c) Calculate the cell potential under standard conditions.
d) Calculate the free energy of the reaction achievable.
e) Calculate the K eq for such a set-up.
f) The salt bridge is comprised of NaNO 3 . Indicate the
direction of ion movement; i.e., towards which compartment
do the Na+ ions migrate?
B) Calculate the cell potential for the disproportionation of Cu+ to Cu0 and Cu2+ under
standard aqueous conditions.
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C) The electrolysis of sodium chloride as a melt produces Na0 metal and chlorine gas,
Cl 2 . In contrast, the electrolysis of NaCl dissolved in water produces 2 gases.
Give balanced chemical equations for both processes.
D) Table 5.1 of your text gives values for the ionization energies for Li0, Na0, and Cs0,
as well as the standard Reduction Potentials; these are repeated below. Give
equations that define these thermodynamic processes; don’t forget to state the
conditions used for the experimental measurements. In a couple of sentences
rationalize the trend observed for the IPE and contrast to the “trend” or discontinuity
in the Standard Reduction Potential.
Ionization Potential Energy
Standard Reduction Potential
Li
526
-3.04
Na
502
-2.71
Cs
382 kJ/mol
-2.92 Volt
Page 5 of 5