CHEM 404 University of New Hampshire Chemistry Worksheet

Chem 404 Review ProblemsInstructions:
 To obtain the 1% bonus credit in Spring 2022 by doing this assignment, you must
complete 9 of the 11 problems (including any parts within each problem you choose).
 To obtain the credit, you don’t need to get the answer completely correct. You will not be
given a grade. But you must make your best attempt by showing all your work on your
page.
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1. This is perfluorodecalin. The questions below refer to this substance.
F F
F
F
F
Properties
Liquid at room temperature
F
F
F
F
F
F
F
F
F
Very low solubility in water
Boiling point is 142 oC
F
F
F F
Dissolves oxygen (O2) very well
a) What atoms are not explicitly shown in this structure?
______________
b) Explain briefly what the symbols shown here are attempting
to represent about the structure of this substance.
c) A mouse can be submerged in perfluorodecalin that is enriched in dissolved oxygen and
continue to breath and stay alive.
i. Predict the polarity of the bonds in this substance and explain your rationale.
ii. Predict the polarity of the entire molecule and explain your rationale.
iii. Using the fundamental ideas of intermolecular forces, explain the solubility
properties of the substance in water and the solubility of oxygen in the substance.
iv. Use the idea of entropy to explain the low solubility of this substance in water.
2. Refer to the molecule on the right side.
a) Draw a sketch to show where all the orbitals that
contribute to SIGMA BONDS are, in correct
geometric relationship.
b) Draw a sketch to show where all the orbitals that
contribute to PI BONDS are, in correct geometric
relationship.
Cl
C
H
C
Cl
C
H
c) Based on your previous sketches, describe the relative positions of the two hydrogen
atoms versus the two chlorine atoms.
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Chem 404 Review Problems
3. This is Penicillin G, an antibiotic. The questions on this page refer to this substance.
5
2
3
8
7
H
6
N
1
CH3
9
N
O
4
CH3
S
O
O
12
HO
10
11
a) Circle the type of hybridization for each numbered atom.
Atom #
Orbital Hybridization
1
no hybrid
sp
sp2
sp3
2
2
no hybrid
sp
sp
sp3
3
no hybrid
sp
sp2
sp3
2
4
no hybrid
sp
sp
sp3
2
sp3
5
no hybrid
sp
sp
6
no hybrid
sp
sp2
sp3
2
7
no hybrid
sp
sp
sp3
8
no hybrid
sp
sp2
sp3
2
9
no hybrid
sp
sp
sp3
sp3
10
no hybrid
sp
sp2
2
11
no hybrid
sp
sp
sp3
12
no hybrid
sp
sp2
sp3
b) The number of pi bonds in Penicillin is:
0
3
6
9
12
c) The number of hydrogen bond “donor” possibilities in this molecule:
0
1
2
6
8
d) Draw the H atoms that are implicit (not shown)?
e) Identify H atoms that will be weak acid protons.
f) Identify locations in the molecule that will act as weak base sites.
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Chem 404 Review Problems
4. Consider this chemical system: H2 (g) + I2 (g) ⇌ 2 HI (g)
You set up a container, and using a gas syringe, inject into it some H2, some I2, and some HI.
When the system establishes equilibrium, you analyze the composition and find 0.15 M H2,
0.10 M I2 and 0.25 M HI.
a) Calculate the value for the equilibrium constant.
b) Give TWO other valid values of concentrations for this system at equilibrium where
the ratios of species are DIFFERENT from the ones given.
c) You do a second experiment, using the same sized container as before, and inject into
it the following quantities: 0.5 moles H2
0.5 moles I2
0.5 moles HI
Does this composition represent an equilibrium composition? Show how you
decide, and explain what will happen to the composition from this point onward.
5. Answer the unrelated questions (a) and (b) below.
a) Identify the following species as (strong or weak), and (acid or base)
HBrO
Strong/Weak
Acid/Base
N(CH3)3
Strong/Weak
Acid/Base
KOH
Strong/Weak
Acid/Base
HNO3
Strong/Weak
Acid/Base
Strong/Weak
Acid/Base
Cl3CO2+
C6H5NH3
Strong/Weak
Acid/Base
b) Lactic acid (byproduct of muscular activity) is dissolved in water to a concentration
of 3.5 x 10-4 M. Its Ka is 1.4 x 10-4. Calculate the expected [H3O+] of this solution.
6. One way to make useful organic substances is to react waste carbon monoxide with
hydrogen. CO (g) + 2 H2 (g) ⇌ CH3OH (g)
a) Is the reaction endo- or exo- thermic?
∆H = – 90.7 kJ
Endo
KP = 0.25 at 350 K
Exo
b) To enhance the quantity of CH3OH (g) that can be produced, what changes would
you make to operating conditions? (Circle choice, and explain how you decided)
Temperature
increase
keep the same
decrease
Volume of reaction chamber
increase
keep the same
decrease
Amount of hydrogen provided
increase
keep the same
decrease
c) Will the following actions help? Explain why or why not.
i. Run cooling coils through chamber to condense CH3OH to a liquid. (Cooling
coils contain running water and provide a cold surface on which to condense
things.)
ii. Increase the pressure by injecting argon gas into the system.
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Chem 404 Review Problems
7. The following questions are based on an initial buffer system consisting of 0.45 M C3H6O3
and 0.25 M C3H5O3Na. (Ka = 1.4 x 10-4)
a) Calculate the pH of the buffer.
b) Write the balanced equation for the chemical equilibrium that underlies the
calculation in part (a).
c) Suggest another composition using this same buffer system such that the buffer
capacity will be one-half what it is initially.
d) You use the initial buffer of 0.45 M C3H6O3 and 0.25 M C3H5O3Na in an application
involving growth of bacteria. After a few days, you measure the pH and find that it is
4.10. What are the concentrations of the buffer components?
8. Consider the following reaction: C3H8 (g) + 5 O2 (g) ⇌ 3 CO2 (g) + 4 H2O (g)
a) Predict the sign of ∆H and ∆S and explain your prediction without looking at data
tables.
b) Calculate the enthalpy, entropy, and free energy changes using the reference table
information at 25 °C.
c) Using the Gibbs equation, verify that your calculations in part (b) are correct.
9. Complete parts (a) and (b) which are related to each other.
a) Create a diagram onto which you can put the following labels and then describe in
words what the diagram is about.
i. activation energy
ii. standard heat of reaction
iii. transition state
b) How will your diagram change if a catalyst is provided? Choose your response below
and briefly explain.
i. The height of the “hill” will get smaller.
ii. The energy of the reactants will decrease.
iii. The energy of the products will increase.
iv. Both ii and iii will happen.
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Chem 404 Review Problems
10. Answer the unrelated questions (a) and (b).
a) Calculate the normal boiling point of ethanol (C2H6O) in °C given that its entropy of
vaporization is 110 J/(K mol) and its enthalpy of vaporization if 38.6 kJ/mol.
b) Consider this reaction:
2 NO(g) + Cl2 (g) ⇌ 2 NOCl (g) Kp = 6.5 x 104
i. At equilibrium, the partial pressures of NO and Cl2 are 0.35 atm and 0.10
atm. Calculate the partial pressure of NOCl at equilibrium.
ii. Calculate the equilibrium constant for
NOCl (g) ⇌ NO(g) + ½ Cl2 (g)
11. Answer the unrelated questions (a) and (b).
a) Sodium chloride can be purified by precipitating it from a saturated brine solution of
impure sodium chloride by adding concentrated HCl to the brine solution.
Write the balanced chemical equilibrium equation that describes the system under
consideration. Explain why adding HCl works.
b) The appropriate rate law for the reaction:
H2 (g) + I2 (g)  2 HI (g)
i. Rate = rate of production of HI
ii. Rate = k [ H2 ] [ I2 ]
iii. Rate = k [ HI ] 2
iv. Rate = k [ HI ] 2
[ H2 ] [ I2 ]
v. Insufficient information to determine
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