Download doc Practice midterm 2

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Last name
First name Student ID Exam Version
C
CHEM204, Fall 2008, Midterm II
Instructor: Dr. Amy S. Blum
November 11, 2008, 6.05 PM to 9.00 PM
Instructions:
Please write your name and student i.d. on this cover page and write your i.d. and exam
version on
the answer sheet provided.
This is a closed book examination. You are only allowed to use your handwritten notes
(one side of
one 8.5" x 11" sheet of paper).
There are 14 pages including this cover page.
There are two parts to the exam; the first part (questions 1 to 20) consists of questions
with
multiple choices. Questions 21 to 26 are problem solving.
Questions 1 to 20 total 50 points out of 100 (each question is worth 2.5 points).
Questions 21 to 26 total 50 points out of 100.
Use your SCANTRON answer sheet to answer questions 1 to 20.
Answer your questions 21 to 26 directly on the exam. You are not allowed any other
notes/sheets in
this exam.
You can only use your own calculator.
If you write your exam problems in pencil (problems 21 to 26), you are not eligible for a
regrade.
Show all intermediate steps used to obtain the final result.
When instructed to use specific constants in a calculation, follow the instructions.
The final results MUST be accompanied by the proper units and signs. Points will be
deducted
when an answer has the wrong sign. Points will be deducted when an answer has
the wrong
units and/or lacks the units.
At the end you will need to hand in the exam questions and answer sheet.
Formula/constants are provided on page 13 of the exam. A periodic table is found on
the last
page.
You must follow the rules and policies of McGill University Academic Integrity.
WARNING: The Examination Security Monitor Program detects pairs of students with
unusually
similar answer patterns on multiple-choice exams. Data generated by this program can
be used as
admissible evidence, either to initiate or corroborate an investigation or a charge of
cheating under
Section 16 of the Code of Student Conduct and Disciplinary Procedures
Good luck!
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First part of the exam: Short answer, multiple choice questions (20 questions, 2.5
points each
question).
Choose the right response to each question, and indicate the corresponding letter in the
answer
sheet.
1) The osmotic pressure pushing water up from the roots to the treetop of a redwood
(105 m
tall) is 10.2 atm at 298 K. If this osmotic pressure arises solely due to NaCl in the leaves
at
the treetop, the NaCl concentration in the leaves must be:
A) 0.834 M
B) 0.417 M
C) 0.208 M
D) 0.104 M
E) 10.2 M
2) A reaction at 312K with G° = –1798 J/mol is comprised of 3 mol of substance ‘A’, 6
mol
of substance ‘B’, and 3 mol of substance ‘C’. If we are observing an equilibrium, then
the
reaction scheme could be:
A) 2A B + C
B) A 2B + C
C) A + B C
D) A + B 2C
E) 2A B + 2C
3) Based on the following figure obtained for a given substance A at pressure P, where
the S
line represents the molar Gibbs free energy for solid A, the L line represents the molar
Gibbs
free energy for liquid A, and the G line represents the molar Gibbs free energy for
gaseous
A:
A) The pressure P corresponds to the triple point pressure.
B) The pressure P lies below the triple point pressure and the solid sublimes.
C) The pressure P lies above the triple point pressure and the liquid evaporates.
D) The larger the temperature the larger the Gibbs free energy of substance A.
E) All of the above are incorrect
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4) Solutions (1M) are prepared for a series of salts. Please indicate which line orders
the
solutions of the various salts from low to high ionic strength (assume all salts completely
dissociate).
A) CaSO4 < KNO3 < NaCl = CaCl2
B) KNO3 < NaCl < CaCl2 < CaSO4
C) NaCl < KNO3 < CaCl2 = CaSO4
D) NaCl < KNO3 = CaCl2 < CaSO4
E) NaCl = KNO3 < CaCl2 < CaSO4
5) The equivalent conductance at infinite dilution for NaNO3 is 121.56 cm2-1equiv-1, that
for
LiNO3 is 110.14 cm2-1equiv-1. Based on these numbers it is safe to say that:
A) o (Na+) - o (Li+) = 121.56-110.14
B) o (NO3
-) = 121.56-110.14
C) A solution of NaNO3 is a poor conductor compared to pure water
D) A solution of LiNO3 is a poor conductor compared to pure water
E) C and D are correct
6) The following plot illustrates the dependence of the Gibbs free energy of a reaction
(rG) on
temperature (T). Based on the plot:
A) The rS >0.
B) At low temperatures the reaction is spontaneous, and at high temperatures the
reaction is
not spontaneous.
C) The rH >0.
D) At low temperatures the reaction is not spontaneous, and at high temperatures the
reaction is spontaneous.
E) All of the above are incorrect.
7) The Helmholtz energy is a criterion of spontaneity
A) When entropy can not be used
B) At constant T and P
C) At constant n (number of moles)
D) At constant T and V
E) All of the above are incorrect
T
rG
0
0
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8) In an ideal solution of a non volatile solute in a volatile solvent the vapor pressure of
the
solvent is lower than that of the pure solvent because:
A) The entropy of the solution is lower than that of the pure solvent
B) The entropy of the solution is higher than that of the pure solvent
C) The entropy of the vapor is lower than that of the pure solvent
D) The entropy of the vapor is higher than that of the pure solvent
E) All of the above are incorrect
9) The Donnan potential across a semi permeable membrane MAINLY arises from:
A) Unequal charge distribution
B) Unequal distribution of diffusible ions
C) Osmotic pressure
D) Uequal distribution of macromolecules
E) All of the above are incorrect
10) The following graph illustrates the phase diagram for carbon (from F.P. Bundy,
Physica A
156, 169 (1989)). Based on the diagram it is safe to say that:
A) Graphite is not thermodynamically stable at P = 1 atm and 298 K (i.e., under our
normal
living conditions).
B) Carbon exists as a liquid at 1 atm and 298 K.
C) Carbon exists as a vapor at 1 atm and 298 K.
D) Diamond is not thermodynamically stable at P = 1 atm and 298 K (i.e., under our
normal
living conditions).
E) All of the above are incorrect.
T (103 K)
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11) By definition, G:
A) Is independent of the temperature.
B) Is the maximum nonexpansion work that can be obtained for a process at constant V
and
T.
C) Is inversely proportional to the temperature.
D) Will be spontaneous at all temperatures and pressures regardless of the reaction
enthalpy
and entropy.
E) Is the maximum nonexpansion work that can be obtained for a process at constant P
and
T.
12) An irreversible isothermal compression of an ideal gas takes place. It is found that
G > 0
for the process. Based solely on the G value:
A) The process occurs spontaneously
B) The process is not spontaneous
C) We can not use G to predict whereas the process is spontaneous or not because
pressure
is not kept constant
D) The system is at equilibrium
E) All of the above are incorrect
13) A large beaker of benzene (C6H6) is left on an open bench in a closed, unventilated
laboratory. The G° for vaporization of benzene at room temperature (25 ºC) = 2820
J/mol.
At equilibrium, the partial pressure of benzene that exists in the room as gas is equal to:
A) 0.13 bar
B) 1.13 bar
C) 0.0 bar (all liquid)
D) 0.56 bar
E) 0.32 bar
14) Given the following plot for the molar Gibbs energy vs. P for a pure substance at
constant T,
one of the statements below regarding states 1, 2 and 3 is correct.
A) The molar Gibbs free energy is the same for states 1, 2 and 3.
B) The molar volume of state1 is smaller than that of state 2, which is in turn smaller
than
that of state 3.
C) The absolute entropy of state 1 is smaller than that of state 2, which is in turn smaller
than that of state 3.
D) The molar volume of state 3 is smaller than that of state 2, which is in turn smaller
than
that of state 1.
1
3
2
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E) All of the above are incorrect.
15) Ions of opposite charge in a solvent of higher dielectric constant than ethanol will be:
A) More associated than in ethanol.
B) Less associated than in ethanol.
C) Equally associated in ethanol and the solvent of higher dielectric constant.
D) The ions do not interact in solution.
E) Not enough information to determine.
16) When 33g of an unknown compound was dissolved in 500 mL H2O, the freezing
point was
observed to be 267.4 K. Given that Kf for water is 1.86 K kg/mol, the molar mass of the
unknown compound is therefore:
A) 22 g/mol
B) 99 g/mol
C) 50 g/mol
D) 25 g/mol
E) 11 g/mol
17) Based on Debye-Huckel limiting law indicate which statement is incorrect.
A) The + of a 1 mM NaCl solution is larger than the + of a 1 mM CaCl2 solution in the
same solvent
B) The + of a 1 mM NaCl solution in water (=78) is larger than the + of a 1 mM NaCl
solution in ethanol (=32)
C) The + of a 1 mM NaCl solution in water is larger than the + of a 1 mM NaCl
solution in
water + 10 mM KNO3
D) The log + of a NaCl solution decreases proportionally to the square root of the ionic
strength
E) The log + of a NaCl solution increases proportionally to the square root of the ionic
strength
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18) Based on the following three plots illustrating the binding of a ligand "L" to a protein
with a
single binding site, where Y is the fractional saturation of sites, we can say:
A) The ligand “L” has a smaller dissociation constant for the protein in case B.
B) The ligand “L” does not bind to the protein in case A.
C) The ligand “L” has a smaller dissociation constant for the protein in case C
D) The ligand “L” has a smaller dissociation constant for the protein in case A.
E) The ligand “L” does not bind to the protein in case B.
19) A reaction from unknown reactants (R): R P is spontaneous at 37 °C and goes to
completion. If the molar entropy of the products (P) is measured to be 460 J/molK, and
71.3
kJ of heat was given off in the process to the surroundings when 1 mol reacted, then the
molar entropy of the reactants has to be:
A) at least -230 J/molK
B) at most 230 J/molK
C) at least 230 J/molK
D) at least 690 J/molK
E) at most 690 J/molK
20) The interior of an enzyme has a dielectric constant resembling that of an organic
solvent.
Therefore,
A) The enzyme denatures in water.
B) The coulombic interactions at a given distance “r” between two charged amino acids
are
stronger within the interior of an enzyme when compared to aqueous solutions.
C) The osmotic pressure increases six fold per mol of enzyme.
D) Opposite charge ions repel each other inside an enzyme.
E) All of the above are incorrect.
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Second part of the exam:
21) (9 points) The concentration of sodium and potassium ions inside and outside of
the cell
membrane are: C x M Na
out
1.4 10
, C x M K
1
out
5 10
, C x M Na 2
3
int
1.0 10
, C x M K
in
1

1 10
.
The enzyme Sodium Potassium ATPase maintains the charge imbalance by
transporting sodium out
of and potassium into the cell. Calculate the total free energy change involved in
transporting 3 mol
of sodium ions out of the cell and 2 mol of potassium ions into the cell at T = 310K.
Assume a
potential difference of =out-in= 0.070V.
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22) (8 points total) An average human with a body weight of 70 kg has a blood volume
of 5 L.
The Henry’s law constant for the solubility of N2 in H2O is 9.04 x 104 atm at 298 K.
Assume that
blood is composed of 100 % water (i.e., that 9.04 x 104 atm is also the value of Henry’s
constant for
blood and that the density of blood is 1 kg/L and blood’s molecular weight is 18 g/mol)
a. (5 points) Calculate the number of moles of nitrogen absorbed in this amount (5L) of
blood in air of composition 80% N2 at sea level, where the pressure is 1 atm, and at a
pressure of 50 atm.
b. (3 points) Assume that the diver accustomed to breathing compressed air at 50 atm
is suddenly brought to sea level, what volume of N2 is released as bubbles in the
diver’s blood stream.
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23) (10 points) The thermodynamic solubility product of CaF2 is 4.0 x 10-11. Assuming
that the
solution is not ideal, and using Debye Hückel law (also, assume molality = molarity),
what is [Ca2+]
in:
a. (7.5 points) 0.02 M Na3PO4
b. (2.5 points) 0.02 M sucrose solution
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24) (12 points) During a protein unfolding reaction, a protein is found to have the
following
unfolding thermodynamic properties:
Ho = 300 kJ/mol, So = 1,000 J/mol-K
a. (3 points) What is the melting temperature (TM) of this protein?
b. (3 points) Replacement of a buried Tyrosine residue by a Glycine residue lowers the
melting temperature to 292 K. Assuming that there is no effect on the entropy
change during unfolding, what is the enthalpy of unfolding for the Glycine mutant
(Ho mut)?
c. (6 points) What fraction of the Glycine mutant is unfolded at the T M of the wild-type
protein (from part 1)?
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25) (6 points) At constant temperature, a solution containing 1 mole of molecule A and
1 mole
of molecule B has a combined partial pressure of 2.5 atm. When 1 more mole of A is
added to the
previous solution, the combined partial pressure rises to 2.67 atm. Assuming that both A
and B
obey Raoult’s law, what is the vapor pressure of a pure solution of A?
26) (5 points) Pressure cooking is a method of cooking in a sealed vessel that does not
permit air
or liquids to escape below a preset pressure. Most pressure cookers sold in Canada
and the U.S.
have an internal pressure setting of about 15 psi (1 atm) above atmospheric pressure.
Knowing that
the normal boiling point (P = 1 atm) of water is 100 Co and its molar enthalpy of
vaporization is
40.79 kJ/mol, at what temperature does water boil in the pressure cooker?
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Possibly Useful Constants
kB = 1.38 x 10-23 J / K
R = 8.314 J / K mol
R = 0.082 L atm / K mol
g = 9.81 m / s2
NA = 6.02 x 1023
F = 96500 J/V mol
electric charge = 1.6 x 10-19 C
Kb(water) = 0.51 K kg/mol
Kf(water) = 1.86 K kg/mol
h = 6.636 x 10-34 Js
F = 96500 C/mol
1 atm = 101 kPa = 760 torr = 1 bar
1 liter = 10-3 m3
1 liter atm = 101.3 J
273 K = 0 degrees C
1 J = 1 kg m2 / s2
1 N = 1 kg m / s2
1 Pa = 1 N / m2
1 cal = 4.184 J
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