Chem 130, Eppley
Fall 2015
Exam 3
Monday, Nov 23, 2015
100 pts
1. (20 pt) Below is a representation of a unit cell of a chloride of chromium (Cr). In addition to
the figure below, there is a computer model at the front or the classroom. Try to figure out
as much as possible using the figure on your test and then use the figure on the computer if
necessary. Each person will have a maximum of 3 min so work efficiently and use the figure
below before you come to the front as much as possible.
a. The large atoms are the chromium ions and the small atoms are the chlorides. What is the
formula of this particular compound, and what is the charge on the chromium ions?
Support your answer carefully. Show your work! (5 pt)
b. What type of packing arrangement do the
larger spheres form in this lattice? (2 pt)
c. Is this an example of a closest packed lattice?
(2 pt)
d. What is the coordination number of the larger spheres? (2 pt)
e. Based on the formula that you wrote in part a, which of the five types of solids should this
compound be. (2 pt)
f.
Based on your answer to part e, what kinds of properties would you expect this solid to
have. Explain the reason for at least two of the properties you mention. (7 pt)
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Chem 130, Eppley
Fall 2015
2. (8 pt total) Potassium azide (KN3) is sometimes added to water to kill bacteria. The related
acid, hydroazoic acid HN3 has a pKa of 4.6.
a. Would you expect KN3 to act as an acid, base or neutral in aqueous solution? (3 pt)
b. If you selected acid or base above, write the equation that would happen in water to
give it those properties. If you predicted neutral, explain why it would be neutral. (5 pt)
3. (9 pt) If you add soluble Hg(NO3)2 to pure water, an insoluble precipitate will form.
a. Write an equation that explains where the precipitate comes from. (4 pt)
b. Propose a chemical to add to the solution and alter the pH that would cause it to
redissolve and become an aqueous Hg2+ ion again (note: HgCl2 is an insoluble
compound!) (3 pt)
c. Would toxic aqueous Hg2+ be available at normal physiological pH’s that are close to pH
= 7? (just yes or no!) (2 pt)
4. (15 pt) For each of questions below, provide the requested answer (5 pt each). Give a one
phrase justification!
a. The conjugate acid of Hcit2-
(cit= citrate)
b. Salts that would produce acidic solutions
NaHCO3
CoCl3 NaClO4
c. The most basic species
HC2O4–
NH3
ClO3–
C2O422
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Chem 130, Eppley
Fall 2015
5. (24 pt) For each of the following statements, justify using the information you’ve learned from
this class. Illustrate your answers with chemical equations, calculations, and/or diagrams- a
picture is frequently worth a thousand words! (8 pt each)
a. The bond length in O2 is shorter than the bond length in O2– which has 1 extra electron.
b. Sodium metal has a lower boiling point than both magnesium and aluminum metal but
they are all relatively high. They also are malleable and conduct electricity.
c. A solution of hypochlorous acid (HClO) has a higher pH than a solution of chlorous acid
(HClO2). A solution of sodium hypochlorite (NaClO) has a higher pH than a solution of
sodium chlorate (NaClO2)
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Chem 130, Eppley
Fall 2015
6.
(6 pt) For the following reaction, fill in the blank in the reaction and show the states of
matter. Label the acid, base, conjugate acid and conjugate base. In addition, say
whether you think the reaction will go to completion and support your answer briefly.
HOBr + ______________  BrO–
7.
+
HBr
(6 pt) Circle the correct answer(s) for each of the questions below:
a. Molecular solids
GaAs
NH4ClO4
SF6
F2
CuZn
b. Lattice structures containing atoms in octahedral holes
NaCl
diamond
CsCl
wurtzite
rutile
c. The molecular orbital shown is a representation of one of the orbitals
listed below. Circle the correct orbital.

2s
2p
*2p
*2p
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Chem 130, Eppley
Fall 2015
8.
(8 pt) The following is a valid Lewis dot structure for the tetrathionate ion (S 4O62-)
that you generated back in Lab 3 and answered some questions about on Exam 2.
Based on this particular Lewis dot structure show the full valence bond description
for tetrathionate. Indicate clearly the hybridization of the atoms, valence electrons
that would reside in the orbitals, the types of bonds involved and which orbitals
would form which bonds. Do your best to draw a representation of the shapes of
the orbitals and the molecule as a whole (hint: If you put as many atoms in the plane
of the paper as you can, it will be easier to draw)
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