Download Inorganic Chemistry 412 / 512

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Inorganic Chemistry 412 / 512
Midterm Exam #2 solutions
100 pts total, 60 minutes
Please show all work, partial credit may be awarded.
1.
Give a balanced chemical reaction or indicate that no reaction occurs for each: [5 pts ea]
(a) Cr2+ (aq) + Fe3+ (aq)
Cr2+ (aq) + Fe3+ (aq) -> Cr3+ (aq) + Fe2+ (aq)
(b) ClF5 + SbF5
ClF5 + SbF5 ->
ClF4SbF6
(c) Xe + Cl2
No reaction
2.
(a) Chromium (II) acetate hydrate is a cluster compound of composition
[Cr2(O2CCH3)4·2H2O]. Ignoring the water molecules, sketch the structure (hint - there is
M-M bonding). [8 pts]
Note: each acetato ligand is bidentate, with one O atom bonding to each metal ion.
(b) Give the electron configuration (filling of σ, π, and δ orbitals) in the cluster. [5 pts]
In this case, we have 2 Cr (II) ions, each is d4. The electron configuration is
therefore σ2π4δ2
(c) What is the Cr-Cr bond order in the cluster ? [4 pts]
4
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(d) Sketch a π−bonding orbital between the Cr ions. [6 pts]
3.
Give one example of an inorganic polymer that contains N in the polymer backbone, and
state one interesting/useful physical or chemical property. [5]
The ones we that we discussed in class:
o oligo- or polyphosphazenes (such as (NPCl2)n) – we talked about synthesis and
structures of these, some are elastomers, some are fire-retardants
o (SN)n – we discussed the structures and metallic/superconducting property of
the polymer (at low T)
4.
Ammonia has a lower molecular mass than NF3, so why is its boiling point much higher?
[6 pts]
Intermolecular hydrogen bonding occurs in NH3 but not NF3
5.
(a) Draw the structure of an oligomeric form of (SbF5)n. [8 pts]
Pictured is Sb4F20, another is the hexamer Sb6F30.
(b) Based on your sketch in part (a), what is the coordination around Sb in liquid SbF5 ?
[4 pts]
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6.
Potassium hydrogen phosphite (K2HPO3) is not stable in aqueous solution. Write a
balanced redox reaction that occurs when it is added to aqueous base. [9 pts]
HPO32- (aq) + OH- (l)
7.
->
PO43- (aq)
+
H2 (g)
The 3+ oxidation state for transition metals can have very different redox properties. For
example, when added to a neutral aqueous solution, TiBr3 will produce H2, but CuF3 will
produce O2. Explain. [8 pts]
3
Ti(III) is a reducing agent, and can reduce water to H2. Ti is an early transition
metal, the effective nuclear charge is relatively low. Cu is late TM (right-hand side
of the d-block), and has a much greater Zeff. It therefore is more diffucult to
oxidize, and Cu(III) is an oxidizing agent, capable of oxidizing water to O2.
8.
Briefly describe the structure of black phosphorous (you do not need to sketch). [6 pts]
Essentially this is the graphite structure, with non-planar sheets. P atoms form 6membered rings with chair-type conformations, each P has 3 single bonds within
the sheet. There are no covalent interactions between sheets.
9.
Multiple choice, 4 points each. Circle the ONE best answer.
a.
Which solute will increase the acidity of a liquid BrF3 solution?
(a) KF (b) CsF (c) AsF5 (d) OF2
(e) SF6
b.
Which of the following species is a strong oxidant that generally reacts with slow kinetics
in aqueous solution?
(a) NO+ (b) Fe2+ (c) Mn2+ (d) ClO4- (e) SO42- (f) HF (g) SiH4
c.
Which is not linear ?
(a) CO2
(b) NO2+
d.
(c) O3
(d) XeF2
(e) I3-
(f) ICl2-
At which pH is the nitrate anion the strongest oxidizing agent?
(a) 0
(b) 3
(c) 7
(d) 14
(e) the oxidizing strength of NO3- is pH independent