Chemistry 6 10:00 Section
Time limit = 3 hours
Final Exam
Spring 2005
Name________________________________________________
There are two sections to this exam. Please read the instructions carefully.
In the first section, there are 13 multiple choice questions, each is worth 8 points. YOU
MUST ANSWER QUESTIONS 1 THROUGH 3 AND THEN ANY 7 OF YOUR
CHOICE. IF YOU ANSWER MORE THAN 7, THE FIRST 7 WILL BE GRADED.
CROSS OUT THOSE YOU DO NOT WISH GRADED OR LEAVE THEM BLANK.
You do not need to show any work for these problems.
In the second section, there are 13 short answer problems and each is worth 12 points.
YOU MUST ANSWER QUESTIONS 1 AND 2 AND THEN ANY 8 OF YOUR
CHOICE. IF YOU ANSWER MORE THAN 8, THE FIRST 8 WILL BE GRADED.
CROSS OUT PROBLEMS YOU DO NOT WISH TO BE GRADED. Show all work for
partial credit.
All submitted work must be your own effort. The Honor Principle applies to your
submission of this exam.
The last 2 pages contain equations and other potentially useful information. Feel free to
tear them off to use during the exam.
Part 1.
__________
Part 2.
1. __________
2. __________
3. __________
4. __________
5. __________
6. __________
7. __________
8. __________
9. __________
10.__________
11.__________
12.__________
TOTAL _________
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PART 1. For these multiple-choice problems, each correct answer is worth 8 points.
It is not necessary to show any work. Circle the correct answer. YOU MUST
ATTEMPT I-1 THROUGH I-3. Then, do 7 problems of your own choosing.
I-1. Arrange in order of decreasing bond length: NF NF+ NFa. NF > NF+ > NF- b. NF+ > NF > NF- c. NF- > NF+ > NF d. NF+ > NF- > NF
I-2. What is the hybridization of each carbon atom in acetic acid?
H3C-C-OH
||
O
a. C:sp C:sp3 b. C:sp2 C:sp
c. C:sp3 C:sp3
d. C:sp3 C:sp2
I-3. Arrange in order of increasing boiling point: NaF Ar CH4 NO
a. CH4 < Ar < NO < NaF
b. NaF < NO < Ar < CH4
c. Ar < CH4 < NO < NaF
d. NaF < CH4 < NO < Ar
I-4. What is the wavelength of an electron whose energy is equal to 8.00 x 10-19 J?
a. 0.55nm
b. 248nm
c. 1.2 x1015nm
d. 3.0 x108nm
I-5. Which one of the following correctly lists the elements in order of increasing
electronegativity?
a. F<Cl<Br<I
b. Cl<Br<I<F c. Cl<Br<F<I
d. I<Br<Cl<F
I-6. The reaction N2O5 → 2NO2 + ½ O2 has a rate constant of 5.7 x 10-2s-1. If at the start
of the reaction, the pressure of N2 O5 is 2.13atm, what will the pressure of N2 O 5 be after
18.7s?
a. 0 atm
b. 0.73 atm c. 1.07 atm
d. 1.84 atm
I-7. Arrange in order of increasing lattice energy: MgO NaF KCl CaS
a. CaS<KCl< MgO<NaF
b. CaS<MgO< KCl<NaF
c. KCl<NaF<CaS<MgO
d. KCl<CaS<MgO<NaF
I-8. Which of the following transition metal ions would be expected to yield colorless
complexes? La3+ Ti3+ Co2+ Fe3+
a. Ti3+ Co2+
b. La3+ Ti3+
3+
3+
c. Ti Fe
d. La3+ Fe3+
I-9. How many unpaired electrons are in CoF63-?
a. 0
b. 2
c. 3
d. 4
I-10. How many nodes are there in the angular part of the 4p wavefunction for
hydrogen?
a. 1
b. 2
c. 3
d. 4
I-11. The wavelength for the n=3 -> n=2 transition in a particular one-electron ion is
72.2nm. What is the identity of the ion?
a. Li2+
b. He2+
3+
c. Be
d. F8-
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I-12. The gas phase reaction 2NO2 + F2 → 2NO2 F has a rate law Rate = k[NO2][F2].
Which one of the following sets of reactants will appear in the rate determining step for
the mechanism consistent with this rate law?
a. 2NO2 and F2 b. NO2, NO2 F and F c. NO2 and F2 d. 2NO2 F
I-13. Consider a particle in a 3-dimensional cubic box. What the degeneracy for the first
excited state of this system?
a. 0
b. 1
c. 2
d. 3
PART 2. For these short-answer problems, each correct answer is worth 12 points.
Show all work. YOU MUST ATTEMPT II-1 AND II-2. Then, do 8 (and only 8)
problems of your own choosing.
II-1. Consider the effect of forming an octahedral complex on the p orbitals of a metal
atom. Determine the energy splitting of the p orbitals (if any) and sketch a crystal field
diagram analogous to that we sketched in class for the d orbitals.
II-2. Which of the following molecules would be stabilized by addition of an electron to
form an anion? Which would be stabilized by ionization to form a cation? Briefly
explain.
C2
N2
CN
NO
II-3. For each of the following molecules/ions:
•draw a Lewis dot structure
•determine the orbital hybridization of the central atom
•indicate the ideal geometry (counting non-bonding electrons as ‘bonds’)
•indicate the actual geometry (the geometry you observe)
The central atom for each molecule is written first.
XeF4
BrF5
SF4
II-4. Consider the hypothetical reaction A → B + ½ D, which occurs via the mechanism
A → B + C, k1
A + C → B + D, k2
Use the steady state approximation to write an expression for [D].
II-5. Cyanate ion, NCO-, and isocyanate ion, CNO-, are isomers. Draw resonance
structures for each of these ions and indicate which one of the resonance structures makes
the most important contribution to the observed geometry.
II-6. For the reaction [Co(NH3)5Cl]2+ + H2O → [Co(NH3)5H2O]3+ + Cl-, the rate constant
at 25°C is 3.06 x 10-3 min-1 and at 30°C, 5.65 x 10-3 min-1. Find the activation energy.
II-7. Consider a He+ atom. Two transitions with the same ni are observed. The high
energy transition terminates at nf = 1 and the other at an unknown quantum level. The
wavelengths of these transitions are 656.5 nm and 23.4 nm. What is the value of the
unknown quantum number? (Do not assume a value for ni.)
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II-8. For each of the following choose the molecule or atom with the higher transition
temperature. Give a one-line explanation of your choice.
(a) Which has the higher boiling point PH3 or CH4?
___________________________________________________________________
(b) Which has the higher boiling point NH3 or PH3?
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(c) Which has the higher boiling point Xe or Ar?
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(d) Which has the higher boiling point CF4 or HF?
___________________________________________________________________
(e) Which has the higher boiling point H3C-O-CH3 or H3C-CH2-O-H?
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(f) Which has the higher melting point CaO or KCl?
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II-9. What is the wavelength associated with a He atom at 298K?
II-10. The cyclopentadienyl anion, C5H6-, has the structure shown below (a ring of five
carbon atoms, each of which is also bonding to a hydrogen atom. Describe the
hybridization at each carbon atom. Is it possible to draw resonance structures for this
ion? If so, how many? (You do not need to draw them).
II-11. The dipole moment of gaseous CsF is 7.88D and the bond length is 0.255nm.
What is the percent ionic character of the Cs-F bond?
II-12. What are the electronic configurations of OF, OF+ and OF-? Compare the bond
energies, bond lengths and magnetic properties of these species.
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Possibly useful information:
kBoltzmann = 1.38 x 10-23 J/K
1nm = 10-9m
R = 8.31 J/mole – K
melectron = 9.11 x 10-31kg
[A] = [A]o e-kt
NA = 6.02 x 1023 mole-1
1/[A] = 1/[A]o + kt
h = 6.62 x 10-34 J•s
k = Ae-Ea/RT
a0 = 0.530Å
k = P πd2 v e-Ea/RT
1Å = 10-8cm
average velocity = (8RT/πM) 1/ 2
p = h/λ
t1/2 = 0.693/k
∆x • ∆p ≥ h/4π
t1/2 = 1/[A]ok
p = mv
E = hν
c = λ/ ν
E = 2.18 x 10-18 J• Z2/n2
c = 3 x 108 ms-1
|∆E| = R•Z2( 1/nf2 - 1/ni2)
K.E. = 1/2mv2 = p2/2m
E = φ + 1/2(mv2), where φ is the threshold energy or the work function
e = 1.60 x 10-19Coulombs
R (Rydberg constant) = 2.18 x 10-18 J = 109678cm-1
1J = 1kg•m2 s -2
1eV = 1.6 x 10-19J
1D = 3.338 x 10-30C•m
µ = Q•d
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2p
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2s
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1s
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Spectrochemical series (partial list)
F- < H2O < NH3 < CN-
red
orange
violet
blue
yellow
green
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