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Chemistry 112
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Exam III Form A
Section
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April 7, 2015
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IMPORTANT: On the scantron (answer sheet), you MUST clearly fill your name, your
student number, section number, and test form (white cover = test form A; yellow
cover = test form B). Use a #2 pencil.
There are 25 questions on this exam. Check that you have done all of the problems and filled
in the first 25 bubbles on the scantron.Your score will be reported in percent (max 100%).
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CHEMISTRY 112 EXAM 3
Apr. 7, 2015
FORM A
--------------------------------------------------------------------------------------------------------------------1. ΔG° for the following reaction is −2879 kJ/mol. What is ΔGf° for glucose (C6H12O6)?
ΔGf° of CO2(g) is −394.4 kJ/mol and Δ Gf° of water is −237.2 kJ/mol
C6H12O6(s) + 6 O2(g) → 6 CO2(g) + 6 H2O(ℓ)
A.
+275.4 kJ/mol
B.
−479.8 kJ/mol
C.
−910.6 kJ/mol
D.
−2247 kJ/mol
E.
+455.3 kJ/mol
ΔG°rxn = −2879 kJ/mol
--------------------------------------------------------------------------------------------------------------------2. The entropy of vaporization (ΔS°vap) for benzene is 96.4 J/K-mol. The enthalpy of
vaporization (ΔH°vap) is 33.9 kJ/mol. What is the boiling point of benzene?
A.
2.81 °C
B.
0.353 °C
C.
93.2 °C
D.
54.8 °C
E.
78.5 °C
--------------------------------------------------------------------------------------------------------------------3. For the redox reaction below, what is the coefficient in front of water when it is
balanced under basic conditions?
Cr(OH)3(s) + ClO3−(aq) → CrO42−(aq) + Cl−(aq)
A.
1
B.
2
C.
3
D.
4
E.
5
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--------------------------------------------------------------------------------------------------------------------4. How many electrons are involved in the redox reaction below when it is balanced
under acidic conditions?
H2O2 (ℓ) → H2O (ℓ) + O2 (g)
A.
0
B.
1
C.
2
D.
3
E.
4
--------------------------------------------------------------------------------------------------------------------5. Which of the following graphs represents what happens to the solubility of BaCO3 as
Na2CO3 is added? The vertical axis indicates the solubility of the BaCO3 and the
horizontal axis represents the concentrations of added Na2CO3.
A.
B.
C.
D.
E.
--------------------------------------------------------------------------------------------------------------------6. How many seconds will be required to produce 1.0 g of chromium metal by the
electrolysis of a K2Cr2O7 solution using a current of 30 amps?
A.
742 s
B.
557 s
C.
371 s
D.
186 s
E.
93 s
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--------------------------------------------------------------------------------------------------------------------7. Solid ammonium nitrate (NH4NO3) is highly soluble in water. When it dissolves at
298 K, the solution gets cold (i.e., the beaker feels very cold). Based on this
information, what is the temperature dependence of ΔG?
A.
ΔG is negative at all temperatures.
B.
ΔG is positive at all temperatures.
C.
ΔG is positive at low temperature and negative at high temperature.
D.
ΔG is negative at low temperature and positive at high temperature.
E.
ΔG is 0; the system is at equilibrium at all temperatures.
--------------------------------------------------------------------------------------------------------------------8. What is ΔG° for the autoionization of water at 298 K?
A.
−79.9 kJ/mol
B.
−34.7 kJ/mol
C.
0.00 kJ/mol
D.
+ 34.7 kJ/mol
E.
+ 79.9 kJ/mol
--------------------------------------------------------------------------------------------------------------------9. Which of the following is not a spontaneous reaction?
A.
Cl2 (g) + 2 I− (aq) → I2 (s) + 2 Cl− (aq)
B.
2 Cu2+ (aq) + 2 H2O (ℓ) → 2 Cu(s) + O2 (g) + 4 H+ (g)
C.
2 Fe2+ (aq) + Br2 (ℓ) → 2 Fe3+ (aq) + 2 Br− (aq)
D.
Sn2+(aq) + 2 Fe3+(aq) → Sn4+(aq) + 2 Fe2+(aq)
E.
Pt (s) + 2 Au+ (aq) → Pt2+ (aq) + 2 Au (s)
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--------------------------------------------------------------------------------------------------------------------10. Which one of the profiles below depicts the correct value for ΔG° for a reaction that
is spontaneous if the reactants and products are at standard conditions at 298 K?
B
A
ΔG°
C
ΔG°
D
ΔG°
ΔG°
E
ΔG°
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--------------------------------------------------------------------------------------------------------------------11. Which one of the following species is the strongest oxidizing agent?
A.
Cl− (aq)
B.
I3− (aq)
C.
Cr3+ (aq)
D.
Mn (s)
E.
H2 (g)
--------------------------------------------------------------------------------------------------------------------12. Which of the following could offer cathodic protection to prevent the rusting of iron?
A.
Cu (s)
B.
Cl– (aq)
C.
Al (s)
D.
Na+ (aq)
E.
Pb (s)
--------------------------------------------------------------------------------------------------------------------13. The pH of a saturated aqueous solution of a manganese(II) hydroxide Mn(OH)2 is
9.83 at 25°C. What is Ksp of Mn(OH)2?
A.
8.10 × 10−6
B.
1.55 × 10−13
C.
2.27 × 10−20
D.
1.83 × 10−11
E.
3.05 × 10−16
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--------------------------------------------------------------------------------------------------------------------Dr. Rick T. Cat is at it again! Newly discovered element Nittnium (Nt) can be utilized in
voltaic cells. Use the voltaic cell diagram below to answer the next THREE questions:
14. If E°cell is 3.14V, what is E°1/2,red for Nt2+(aq) at 25 oC?
A.
1.48 V
B.
4.80 V
C.
6.28 V
D.
0.00 V
E.
−1.57 V
--------------------------------------------------------------------------------------------------------------------15. What is the value of ΔG0 at 25 oC for the Nittnium/Aluminum cell pictured above?
A.
+1818 kJ/mol
B.
−606 kJ/mol
C.
−909 kJ/mol
D.
+909 kJ/mol
E.
−1818 kJ/mol
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--------------------------------------------------------------------------------------------------------------------16. A graduate student is tasked with investigating how the Nittnium/Aluminum cell
voltage is affected by changing the concentrations in the compartments. What is
Ecell at 25 oC when [Al3+] = 0.3 M and [Nt2+] = 5.0 × 10−5 M?
A.
1.87 V
B.
2.32 V
C.
4.40 V
D.
3.95 V
E.
3.02 V
--------------------------------------------------------------------------------------------------------------------17. A solution contains 2.0 × 10−4 M Ag+(aq) and 1.5 × 10−3 M Pb2+(aq). When solid
NaBr is added, which of the following statements is true?
Ksp of AgBr = 7.7 × 10−13; Ksp of PbBr2 = 6.6 × 10−6?
A.
NaBr will precipitate first.
B.
AgBr will precipitate first.
C.
PbBr2 will precipitate first.
D.
AgBr and PbBr2 will precipitate at the same time.
E.
No precipitate will form at all when [Br−] = 0.01 M.
--------------------------------------------------------------------------------------------------------------------18. The addition of which of the following will result in an increase in the solubility of
CuCO3 (Ksp = 2.3 × 10−10) at 25°C?
i. HCl
ii. NH3
iii. NaNO3
iv. CuSO4
A.
ii only
B.
iv only
C.
i and ii only
D.
iii and iv only
E.
i, ii, and iii only
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--------------------------------------------------------------------------------------------------------------------19. In a lead acid battery, the following unbalanced redox reaction takes place during
electrolysis when the battery is re-charging:
PbSO4(s) + H2O(ℓ) → PbO2(s) + Pb(s) + SO42–(aq) + H+(aq)
(Eocell = – 2.041V)
Which one of the following statements is true concerning this process?
A.
This is a reaction in which the lead in PbSO4(s) is both oxidized and reduced.
B.
Electrons in this electrolysis flow from the cathode into the anode.
C.
Four electrons are involved in the redox process.
D.
This electrolysis reaction has a negative ΔGo and can do work.
E.
Keq > 1 for this reaction.
--------------------------------------------------------------------------------------------------------------------20. In the presence of aqueous ammonia (NH3), Ag+ forms the complex ion [Ag(NH3)2]+.
What is the concentration of free (uncomplexed) Ag+ (aq) in solution when 0.20
mole of AgNO3 is dissolved in 1.0 L solution of ammonia when there is 2.0 M NH3
present at equilibrium? Kf of [Ag(NH3)2]+ = 1.5 × 107.
A.
1.4 × 10−4 M
B.
0.20 M
C.
6.7 × 10−9 M
D.
7.5 × 105 M
E.
3.3 × 10−9 M
--------------------------------------------------------------------------------------------------------------------21. What is the molar solubility of NiCO3 in a solution with equilibrium [NH3] = 0.24 M?
NiCO3, Ksp = 1.3 × 10−7; [Ni(NH3)6]2+, Kf = 1.2 × 109
A.
0.24 M
B.
2.98 M
C.
6.12 M
D.
0.17 M
E.
0.12 M
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--------------------------------------------------------------------------------------------------------------------22. Put these in order of increasing molar solubility in water.
i.
Fe(OH)2
Ksp = 7.9 × 10−16
ii.
BaSO4
Ksp = 1.1 × 10−10
iii.
Ag2CO3
Ksp = 8.1 × 10−12
A.
i < iii < ii
B.
iii < i < ii
C.
ii < i < iii
D.
iii < ii < i
E.
i < ii < iii
--------------------------------------------------------------------------------------------------------------------23. A voltaic cell is constructed:
Mn(s) | Mn2+(0.5 M, aq) || Cu2+(0.5 M, aq) | Cu(s)
Which of the following would cause Ecell to increase?
i. Adding water to the anode compartment.
ii. Adding water to the cathode compartment.
iii. Increasing [Cu2+] to 1.5 M.
iv. Increasing [Mn2+] to 1.5 M.
v. Doubling the mass of Mn (s)
A.
i and iii
B.
ii and iv
C.
i, iii, and v
D.
ii, iv, and v
E.
Ecell can not be changed by the above actions.
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--------------------------------------------------------------------------------------------------------------------24. When an aqueous solution that is 1 M each in HCl, ZnCl2 and CoBr2 is electrolyzed,
the elemental products formed initially at the cathode and anode are, respectively
A.
Zn(s) and Cl2(g).
B.
Co(s) and Br2(g).
C.
H2(g) and Cl2(g).
D.
Zn(s) and Br2(g).
E.
H2(g) and Br2(g).
--------------------------------------------------------------------------------------------------------------------25. After the glucose-phosphate species forms in the metabolic process, the isomerization
of glucose-phosphate to fructose-phosphate occurs. If the equilibrium constant for the
isomerization reaction at 37°C (body temperature) is 0.65, what is the value of ΔG when
the ratio of glucose-phosphate to fructose-phosphate is 10 to 1?
glucose-phosphate → fructose-phosphate
A.
−0.48 kJ/mol
B.
−0.63 kJ/mol
C.
−1.11 kJ/mol
D.
−4.82 kJ/mol
E.
−6.93 kJ/mol
Keq = 0.65
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End of Exam
Chem 112 Spring 2015
Exam 3 Answer Key
4/7/15
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CHEM 112
Spring 2015
xam 3 – Form A
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