Chemistry 112
Practice Exam 3B
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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. The maximum score on this exam is 25 points. Your score will be
reported in percent (max 100%).
Exam policy
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Calculators with text-programmable memory are not allowed.
Relevant data and formulas, including the periodic table, are attached at the end of this exam.
Your grade will be based only on what is on the scantron form.
The answer key will be posted on the web after the exam (on the Exam Schedule page).
You must turn in your cover sheet with your scantron answer form.
You MUST bubble in all of your answers before the time is up; you may not bubble your scantron
after the time is called.
Hints
As you read the question, underline or circle key words to highlight them for yourself. Avoid
errors from "mis-reading" the question.
Pay attention to units and magnitudes (decimal places) of numbers obtained from calculations.
There is no penalty for guessing.
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Chem 112 EXAM 3
PRACTICE EXAM 3B SPRING 2016
-------------------------------------------------------------------------------------------------------------------1. Consider the following titration curve for the complete titration of a species. Which of the following
statements is/are TRUE?
i. The acid is a diprotic acid
ii. The acid is a triprotic acid
iii. Point E represents the third equivalence point
iv. Point A represents the first half-equivalence point
A. i only
B. ii only
C. i and iv only
D. ii and iii only
E. ii, iii, and iv only
-----------------------------------------------------------------------------------------------------------2. The famous scientist, Rick T. Cat, found himself at the Mt. Nittany Medical Center with symptoms
including hyperventilation, vomiting, dizziness, and a diffuse burning sensation. Upon examination, it
was found that his blood concentration of H2CO3 was 1.5 mmol/L, and the concentration of HCO3− in his
blood was 30 mmol/L. What was the pH of his blood?
Ka1 of H2CO3 = 4.3 × 10−7
Ka2 of H2CO3 = 5.6 × 10−11
A.
B.
C.
D.
E.
7.33
11.55
6.37
7.67
7.51
2
----------------------------------------------------------------------------------------------------------3. How many electrons are involved in the redox reaction below when it is balanced under acidic
conditions?
H2O2 (ℓ) → H2O (ℓ) + O2 (g)
A.
B.
C.
D.
E.
0
1
2
3
4
----------------------------------------------------------------------------------------------------------4. The drawing below represents a buffer composed of equal concentrations of a weak acid HA and its
conjugate base A−. The solution is 1 M in each component, and the total volume is 1 L.
Which drawing below illustrates the composition of the solution after 10 mL of 2 M HCl is added?
----------------------------------------------------------------------------------------------------------5. 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
----------------------------------------------------------------------------------------------------------3
6. Given 1.00 L of a solution that is 0.100 M in sodium propionate (NaC3H5O2) and 0.300 M in propionic
acid (HC3H5O2), what is the pH after 0.0400 mole of HNO3 is added? (Assume that the volume does not
change upon addition of the HNO3.)
(Ka for HC3H5O2 = 1.3 × 10−5)
A. 4.50
B. 4.08
C. 3.96
D. 4.13
E. 4.62
----------------------------------------------------------------------------------------------------------7. Which of the following graphs represents what happens to the solubility of the insoluble salt BaCO3(s)
as Na2CO3 is added?
-------------------------------------------------------------------------------------------------------------------8. What is the oxidation state of chromium in chromic acid, H2CrO4?
A. +8
B. +6
C. +2
D. 0
E. −2
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----------------------------------------------------------------------------------------------------------9. 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.
B.
C.
D.
E.
742 s
557 s
371 s
186 s
93 s
----------------------------------------------------------------------------------------------------------10. Which of the following is not a spontaneous redox reaction under standard conditions at 25oC?
A.
B.
C.
D.
E.
Cl2 (g) + 2 I− (aq) → I2 (s) + 2 Cl− (aq)
2 Cu2+ (aq) + 2 H2O (ℓ) → 2 Cu(s) + O2 (g) + 4 H+ (g)
2 Fe2+ (aq) + Br2 (ℓ) → 2 Fe3+ (aq) + 2 Br− (aq)
Sn2+(aq) + 2 Fe3+(aq) → Sn4+(aq) + 2 Fe2+(aq)
Pt (s) + 2 Au+ (aq) → Pt2+ (aq) + 2 Au (s)
----------------------------------------------------------------------------------------------------------11. Which one of the following species is the strongest oxidizing agent at 25oC?
A.
B.
C.
D.
E.
Cl− (aq)
I3− (aq)
Cr3+ (aq)
Mn (s)
H2 (g)
------------------------------------------------------------------------------------------------------------
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12. Oh no! A research student working in the lab of Rick T. Cat accidentally mixed up three unlabelled
bottles of 0.1 M acid solutions. The three acids are acetic acid, hypochlorous acid, and nitric acid. In
order to figure out the identities of the three solutions, Dr. Cat titrates each of the three acid solutions with
0.10 M NaOH. The following data were obtained at 25 oC:
Ka (CH3COOH) = 1.8 × 10−5
Ka (HClO) = 3.5 × 10−8
What are the identities of the acid solutions?
Acid 1
Acid 2
Acid 3
A.
HClO
HNO3
CH3COOH
B.
HClO
CH3COOH
HNO3
C.
CH3COOH
HClO
HNO3
D.
CH3COOH
HNO3
HClO
E.
HNO3
HClO
CH3COOH
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----------------------------------------------------------------------------------------------------------13. Which of the following could offer cathodic protection to prevent the rusting of iron at 25oC?
A. Cu (s)
B. Cl– (aq)
C. Al (s)
D. Na+ (aq)
E. Pb (s)
----------------------------------------------------------------------------------------------------------14. A scientist titrates 100 mL of a 0.2 M solution of hypobromous acid (HBrO) with 0.1 M NaOH.
What is the pH of the solution after 400 mL of NaOH is added at 25oC?
Ka (HBrO) = 2.5 × 10−9
A. 1.4
B. 3.8
C. 7.0
D. 12.6
E. 8.3
-----------------------------------------------------------------------------------------------------------15. 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:
16. If E°cell is 3.14 V, what is E°1/2(red) for Nt2+(aq) at 25oC?
A. 1.48 V
B. 4.80 V
C. 6.28 V
D. 0.00 V
E. −1.57 V
----------------------------------------------------------------------------------------------------------17. If E°cell is 3.14 V, how much work can be done by the Nittnium/Aluminum cell pictured above under
standard conditions at 25oC?
A. 1818 kJ
B. 606 kJ
C. 909 kJ
D. 909 kJ
E. 181.8 kJ
----------------------------------------------------------------------------------------------------------
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18. In one of the steps in the refining of iron ore in a blast furnace, liquid iron is created in an incredibly
hot environment as in the reaction below. What is the reducing agent in this reaction?
Fe3O4 (s) + 4 H2 (g) + heat → 3 Fe (ℓ) + 4 H2O (ℓ)
A)
B)
C)
D)
E)
Fe3O4 (s)
H2 (g)
heat
Fe (ℓ)
H2O (ℓ)
----------------------------------------------------------------------------------------------------------19. 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 at 25oC?
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.
----------------------------------------------------------------------------------------------------------20. 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. K2CO3
iii. NaNO3
iv. CuSO4
A. i only
B. iv only
C. i and ii only
D. iii and iv only
E. i, ii, and iii only
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----------------------------------------------------------------------------------------------------------21. 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.
B.
C.
D.
E.
This is a reaction in which the lead in PbSO4(s) is both oxidized and reduced.
Electrons in this electrolysis process flow from the cathode to the anode.
Four electrons are transferred in the redox process.
This electrolysis process has a negative ΔGo and can do work.
Keq > 1 for this reaction.
----------------------------------------------------------------------------------------------------------22. Put these in order of increasing molar solubility in water at 25oC:
i.
ii.
iii.
Fe(OH)2
BaSO4
Ag2CO3
Ksp = 7.9 × 10−16
Ksp = 1.1 × 10−10
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 scientist titrates 50 mL of a 0.5 M solution of methylamine (CH3NH2) with 1 M HCl. What is the
pH of the solution after 12.5 mL of HCl is added at 25 oC?
Kb of methylamine = 4.2 × 10−4
A.
B.
C.
D.
E.
3.4
5.9
7.0
10.6
13.7
-----------------------------------------------------------------------------------------------------------
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24. 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 at 25oC?
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.
----------------------------------------------------------------------------------------------------------25. When an aqueous solution that is 1 M each in HCl, ZnCl2 and CoBr2 is electrolyzed, what are the
elemental products formed initially at the cathode and anode at 25oC, respectively?
A.
B.
C.
D.
E.
Zn(s) at the cathode and Cl2(g) at the anode.
Co(s) at the cathode and Br2(g) at the anode.
H2(g) at the cathode and Cl2(g) at the anode.
Zn(s) at the cathode and Br2(g) at the anode.
H2(g) at the cathode and Br2(g) at the anode.
-----------------------------------------------------------------------------------------------------------END OF EXAM
------------------------------------------------------------------------------------------------------------
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ANSWER KEY:
1. C
2. D
3. C
4. C
5. E
6. D
7. A
8. B
9. C
10. B
11. B
12. B
13. C
14. D
15. B
16. A
17. A
18. B
19. B
20. A
21. A
22. E
23. D
24. A
25. E
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