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1
Inorganic Chemistry 411/511
110 minutes; 200 points total
Show your work for partial credit.
Final Exam
1. Draw the molecular geometry and indicate any deviations from ideal VSEPR
coordination angles. Give the point group for each molecule.
(a)
[9 pts] trans-SF4Cl2
D4h, tetragonal.
(c)
(b)
[9 pts] BCl3
D3h, trigonal planar
[7 pts] Is either of the above molecules polar? Explain using symmetry rules.
Neither is polar. Both are in D groups. Or, both have an inversion center.
2
2. (a)
[14 pts] Write down a Born-Haber analysis (give all the reaction steps) needed to
estimate Hf for LiI (s) from the elements in standard states. Label each reaction
step with an appropriate energy term (such as I, Ea, ΔHL, etc).
Correct reactions steps, 6
Correct label for energetics (I, Ea, ΔHL, etc), 4
Correct summation and signs, 2
(b)
[7 pts] Is LiI (s) more or less soluble in polar solvents than LiF (s)? Explain
briefly.
Large small combination has lower relative lattice enthalpy compared to solvation
enthalpy, and LiI is much more soluble.
3
3. (a) [14 pts] Construct an MO diagram for the HF (g), including valence atomic and
molecular orbitals, symmetry labels, and the electron filling of the MO's.
See Fig in text
(b)
[6 pts] Draw a figure showing the geometry of the LUMO orbital on HF.
4
4. A Latimer diagram for Mn at pH = 0
1.09
-
-
MnO4
(a)
MnO3
2.9
0.95
MnO2
Mn
3+
1.5
Mn
2+
-1.18
Mn
-
[10 pts] What is the standard potential for reduction of MnO4 to Mn2+ at pH=0 ?
E = (1.09*2 + 2.9 + 0.95 + 1.5 – 1.18)/5 = + 1.27 V
(b)
[10 pts] Does Mn3+ disproportionate spontaneously in aqueous acid? Explain.
Yes. For the reaction: Mn3+ → Mn2+ + MnO2,
the potential is 1.5 – 0.95 = + 0.65 V. Thermodynamically spontaneous.
(c)
-
[10 pts] Write a balanced half-reaction for the reduction of MnO4 to Mn2+ in
acidic solution.
-
MnO4 + 8H+ + 5e- → Mn2+ + 4H2O
(d)
[10 pts] Calculate the potential for the half-reaction in part (c) at pH = 2.
The Nernst equation is E = E0 – (0.059 V/ n) log Q
E = 1.27 – (0.059/5) log(1/[H+]8)
= 1.27 – 0.059 * 16/5
= 1.08 V
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5. (a)
[6 pts] Write out the full name of the complex [Cr(NH3)2(NCS)4]1di(ammine)tetrakis(isothiocyanato)chromate(III) or chromate(1-)
(b)
[7 pts] Sketch the trans isomer of the complex above)
Oh angles = 2 pts, trans = 2 pts, correct linkages = 2 pts
(b)
[10 pts] Write a d orbital energy level diagram Fe(III) in an Oh field, label the dorbitals with (z2, x2-y2, xy, xz, and yz) and also give the orbitals symmetry labels.
(c)
[10 pts] Calculate the ligand field stabilization energies (LFSE) in terms of O
for the two electron configurations in part (a).
High spin LFSE = zero; low spin is LFSE = 2.0 ΔO
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6. The F-NMR spectrum below was collected on a fluorinated compound at low
temperature.
(a)
[10 pts] Is this compound ClF3 , BF3, SeF4 or PF5? Explain your reasoning in
detail.
The 2:1 intensities and doublet/triplet splitting indicates 3 F’s in two
environments (2 of one type and 1 of another). This is the case for ClF3 at low
temp, with one equatorial and two axial F’s. The other reasonable candidate with
3 F’s, BF3, is trigonal planar and has all the F’s equivalent, so only a single peak
will be seen at all temps.
(b)
[7 pts] Explain or sketch the changes in the NMR spectrum above as the sample
is heated. If the spectrum should be temperature independent, just write “No
Change”.
When the temp is sufficiently high to enable rapid exchange (fluxionality), only a
single peak will be seen.
7. [10 pts] Show with a simple picture how the π acceptor orbital on CN¯ pictured below
interacts with d orbitals on transition metal cations.
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8. [10 pts] Write a balanced reaction showing how H2 is generated on an
industrial scale.
CH4 (g) + H2O (g) → CO (g) + 3 H2 (g)
Or
C (s) + 2 H2O (g) → CO2 (g) + 2 H2 (g)
Or, electrolysis is OK
9. [4 pts each] Circle the ONE best choice.
(a)
Wurtzite structure has the stacking sequence of (AaBb)n, where uppercase letters
are anions and lowercase are cations. What is the coordination geometry around
8
anions in the lattice?
(1) tetrahedral
(2) square planar
(3) octahedral
(4) trigonal prismatic (5) linear
(6) trigonal bipyramidal
(b)
Which of the following octahedral complexes has two geometric isomers?
(1) [FeCl(OH2)5]2+
(2) [IrCl3F3]2(3) [RuCl4(bipy)]2+
(4) [CoBr2Cl2(NH3)2]
(5) [W(CO)6]
(6) [CrCl5(NH3)]2-
(c)
Which of the following ligands will form the strongest complex with the soft acid
Hg2+ ?
(1) O2- (2) S2- (3) Se2- (4) all complexes will have the same Kf
(d)
Based on d electron configurations, which of the following is NOT likely to be
square planar?
(1) [AgCl4]¯ (2) [AuF4]¯ (3) [Pd(CN)4]2- (4) [RhF4]2- (5) [PtCl4]2-
(e)
Which of the following will rapidly react with water to form H2 ?
(1) O2
(2) F2
(3) HF2¯
(4) CH4
(5) SF6
(6) CaH2
(f)
Using Pauling’s rules, what is the expected pKa for phosphorous acid, H3PO3?
(1) 0
(2) 1
(3) 3
(4) 7
(5) 8
(6) 8.3
9
10
Oh E
8C3 6C2 6C4 3C2 i
6S4 8S6 3
h
6
d
A1g
1
1
1
1
1
1
1
1
1
1
A2g
1
1
-1
-1
1
1
-1
1
1
-1
Eg
2
-1
0
0
2
2
0
-1
2
0
T1g
3
0
-1
1
-1
3
1
0
-1
-1
T2g
3
0
1
-1
-1
3
-1
0
-1
1
A1u
1
1
1
1
1
-1
-1
-1
-1
-1
A2u
1
1
-1
-1
1
-1
1
-1
-1
1
Eu
2
-1
0
0
2
-2
0
1
-2
0
T1u
3
0
-1
1
-1
-3
-1
0
1
1
T2u
3
0
1
-1
-1
-3
1
0
1
-1
x2+y2+z2
(z2, x2-y2)
(xz, yz, xy)
(x, y, z)