Chemistry 1312
Exam 3, Spring, 2003
I. Multiple Choice (96 points) Select the best response for each of the
following and record on the scantron. Do
not erase; erasures may result in a misgrading of your response.
1. Which of the following complexes has a metal ion with an
oxidation state of zero?
a. [CuF4]2-
b. [Fe(CN)6]4-
c. [Co(NH3)4Cl2]+
d. [Cr(CO)6]
e. [Pt(NH3)2Cl2]
2. Predict which of the following complexes is most stable.
a. [CoEDTA]-
b. [Co(en)3]3+
c. [Co(H2O)6]3+
d. [CoF6]3-
e. [Co(NH3)6]3+
3. In the reaction, NO(g) + O3(g)
® NO2(g)
+ O2(g), the rate law is, rate = k [NO][O3]. Which of the following statements is true?
a. a
plot of ln[NO] vs. time when the [O3] is held constant yields a
straight line with a negative slope
b. a plot of 1/[NO] vs. time when the
[O3] is held constant yields a straight line with a positive slope
c. the units of the rate constant are
mol/L•s
d. a plot of ln[NO] vs. time when the
[O3] is held constant yields a “decay” curve
e. a plot of ln[NO] vs. 1/T when the
[O3] is held constant yields a straight line with a negative slope
4. Which of the following pairs of octahedral complexes are optical
isomers? “A”, “B”, and “C” represent
different monodentate ligands and the curved line represents a bidentate ligand.
figures were not transferred with this file
Answer: b
5. What is the rate law for the reaction, 2 NO(g) + O2(g) ® 2 NO2(g) is
a. rate = k[NO][O2]
b. rate = k[NO]2[O2]
c. rate = k[NO][O2]2
d. rate = k[NO]2[O2]2
e. more
information is necessary
6. Which of the following Pt2+ square planar complexes
can form cis/trans isomers?
a. [Pt(NH3)2Cl2]
b. [Pt(NH3)Cl3]
c. [PtCl4]2-
d. [Pt(NH3)3Cl]
e. [Pt(NH3)4]2+
7. For the following two-step mechanism, identify the substance
that is the intermediate;
O3 + NO ® O2 + NO2
NO2 + O ® NO
+ O2
a. O3
b. NO
c. O2
d. NO2
e. O
8. The plot at
right could represent one of the following relationships for the
reaction 3A + B ®
products. Which one?
a. 1/[A] vs. T for a reaction that is
second order in A
b. ln k vs. 1/T for the reaction
c. ln [A] vs. 1/time for a reaction
that is first order in A
d. 1/[A]
vs. time for a reaction that is second order in A
e. [A] vs. T for a reaction that is
first order in A
9. A catalyst increases the
rate of a chemical reaction by
a. changing the enthalpy of reaction
for the reaction
b. always providing a surface on which
molecules can react
c. changing the products formed in the
reaction
d. lowering
the overall activation energy for the reaction
e. changing the geometry of the
activated complex
10. CN- is a strong ligand while F- is considered
a weak ligand. For the two complexes
[CoF6]3- and [Co(CN)6]3-
a. both are diamagnetic
b. [CoF6]3- is
diamagnetic but [Co(CN)6]3- is paramagnetic
c. [CoF6]3-
is paramagnetic but [Co(CN)6]3- is diamagnetic
d. Both [CoF6]3-
and [Co(CN)6]3- are paramagnetic but [CoF6]3-
has more unpaired electrons
e. Both [CoF6]3-
and [Co(CN)6]3- are paramagnetic but [Co(CN)6]3-
has more unpaired electrons
11. The decomposition of hydrogen peroxide follows first order
kinetics. This means that
a. an increase in the hydrogen
peroxide concentration has no affect
on the reaction rate
b. the
rate constant is inversely proportional to the time for half the initial
concentration of hydrogen peroxide
to decompose
c. the order of the reaction increases
with temperature
d. the rate constant has units of
L/mol•s
e. the rate law is, rate = k[H2O]-1
12. If increasing the concentration of X3 in the reaction, X3 + 2 Y2 ® products, causes no change
in the reaction rate, then it can be concluded that
a. X3 is a gaseous
substance
b. X3 has a very long
half-life
c. the
reaction is zero order with respect to X3
d. the reaction is first order with
respect to X3
e. X3 is the catalyst in
the reaction
13. Consider the
reaction profile at right. “A” labels
a. the exothermicity of the reaction
b. the activation energy for the
forward reaction
c. the
activation energy for the reverse reaction
d. the transition state for the reaction
e. the endothermicity of the reaction
14. The aqua complex ion that appears green is
a. [Cu(H2O)4]2+
b. [Co(H2O)6]2+
c. [Fe(H2O)6]2+
d. [Ni(H2O)6]2+
e. [Cr(H2O)6]2+
15. [Fe(CN)5OH]3- forms a low-spin complex. How many electrons are unpaired in the d-orbitals
of iron?
a. 0
b. 1
c. 2
d. 3
e. 5
16. Based upon simple crystal field theory, the metal ion which would
be least likely to exhibit color in
an octahedral complex is
a. Fe3+
b. Cr3+
c. Ni2+
d. Mn2+
e. Cd2+
17. A chemical process is known to be exothermic. Therefore the relationship between the
activation energy for the forward reaction Ef, and that for the
reverse reaction, Er, is
a. Ef = Er
b. Ef > Er
c. Ef = Er = 0
d. Ef
< Er
e. need
more information
18. For the splitting of the d-orbitals in an octahedral complex, which
orbitals are of highest energy?
a. dz2 only
b. dz2
and dx2 - y2 only
c. dxy, dyz, dz2
only
d. dxy, dyz, dxz
only
e. dxy and dyz
only
II. Exercises (41 points). The organization of all exercises must be
shown clearly and legibly in order to receive any partial credit. Answers without a logical problem setup will
receive only 10% credit.
1. (15 points) The
decomposition of nitramide, NH2NO2, follows first order kinetics with a half‑life of 123 minutes.
a. (5 pts) What is the rate constant for its
decomposition?
k = 5.63 x 10-3 min-1
b. (10 pts) How long (in hours) does it take for 60% of a
sample of nitramide to decompose?
2.71 hours
2. (26
points) The following rate data were collected
for the reaction,
3 A +
B3 ® C2
+ D
Trial No. [A]o [B3]o rate, [C2]/s
1 0.60 0.40 17x 10-3
2 0.20 1.20 5.7 x 10-3
3 0.20 0.40 1.9 x 10-3
4 0.30 0.60 ??
a. (3 pts) The order of the reaction with respect to [A]
is _____second______
b. (3 pts) The order of the reaction with respect to [B3]
is ______first_______
c. (5 pts) The rate law for the reaction is
rate = k[A]2[B3]
d. (10 pts) The rate constant for the reaction is (label
with appropriate units)
k = 0.118 L2/mol2•s
e. (5 pts) The predicted reaction rate for Trial No. 4
is
rate = 6.4 x 10-3 mol/L•s