Chemistry 112
Practice Exam 3C
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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.
Chem 112 EXAM 3
PRACTICE EXAM 3C SPRING 2016
---------------------------------------------------------------------------------------------------------------------------1. Which one of the following species can offer cathodic protection to prevent the rusting of Fe (s) at
25oC?
A. Na+ (aq)
B. Br2 (ℓ)
C. H+ (aq)
D. Ni (s)
E. Zn (s)
---------------------------------------------------------------------------------------------------------------------------2. Almandine is the mineral name of the deep red gemstone known as a garnet, and has the formula
Fe3Al2(SiO4)3, where iron is in the +2 oxidation state. What is the oxidation state of oxygen in
almandine?
A. –2
B. –1
C. –4
D. 0
E. +1
---------------------------------------------------------------------------------------------------------------------------3. A chemical company uses mercury ions in a production line, and needs to reduce the concentration of
toxic Hg2+ as much as possible before dumping the wastewater. The company decides to try to precipitate
the mercury as HgS(s). If the equilibrium concentration of S2– in the solution is 0.75 M, what is the Hg2+
concentration in a saturated solution at 25°C? The Ksp of HgS is 4.0 x 10–53.
A. 6.3 x 10–27 M
B. 8.4 x 10–27 M
C. 5.3 x 10–53 M
D. 4.0 x 10–53 M
E. 7.1 x 10–53 M
---------------------------------------------------------------------------------------------------------------------------4. How many electrons are transferred in the following unbalanced redox reaction?
Al (s) + Cd(NO3)2 (aq) → Al(NO3)3 (aq) + Cd (s)
A. 1
B. 2
C. 3
D. 5
E. 6
---------------------------------------------------------------------------------------------------------------------------5. What is the pH of a mixture of 2.7 mmol/L HF and 19 mmol/L NaF?
Ka(HF) = 7.1 x 10¯4
A.
B.
C.
D.
E.
2.30
3.15
4.00
5.51
8.76
---------------------------------------------------------------------------------------------------------------------------6. Much to the surprise of everyone, Nittnium (Nt) can be incorporated into redox reactions! Which
species acts as the reducing agent in the following redox reaction?
Nt3+ (aq) + H2O (ℓ) + MnO2 (s) → Nt (s) + MnO4– (aq) + 2H+ (aq)
A.
B.
C.
D.
E.
Nt3+ (aq)
H2O (ℓ)
MnO2 (s)
H+ (aq)
MnO4– (aq)
---------------------------------------------------------------------------------------------------------------------------7. For which one of the following titrations would the pH < 7 exactly at the equivalence point?
A. HCl titrated with NaOH
B. CH3COOH (acetic acid) titrated with KOH
C. HCN titrated with NaOH
D. C6H5NH2 titrated with HBr
E. HClO3 titrated with Ca(OH)2
---------------------------------------------------------------------------------------------------------------------------8. Which one of the following statements is TRUE regarding electrochemistry?
A. Electrons flow from the cathode to the anode in electrolytic cells.
B. When products are favored in a redox reaction, Eocell is negative, Keq < 1, and ΔGo is positive.
C. In a voltaic cell, ΔG = 0 and Ecell = 0 at equilibrium.
D. In an electrolytic cell, oxidation occurs at the cathode.
E. In the salt bridge of a voltaic cell, anions flow towards the cathodic compartment and cations flow
towards the anodic compartment.
----------------------------------------------------------------------------------------------------------------------------
9. Lithium-ion batteries are commonly used in portable devices such as cell phones, laptop computers,
and digital cameras because these batteries are light and can be re-charged hundreds of times. Given the
two half-reactions involved in a lithium-ion battery below, what is the maximum amount of work the
battery can do (in kJ) under standard conditions at 25oC?
A.
B.
C.
D.
E.
Half Reaction
Eo1/2 (red) (V)
Li+ (aq) + 1e– → Li (s)
–3.05
Li+ (aq) + CoO2 (s) + 1e– → LiCoO2 (s)
+0.35
328.1 kJ
3.28 x 105 kJ
260.6 kJ
2.61 x 105 kJ
294.3 kJ
---------------------------------------------------------------------------------------------------------------------------10. A titration enthusiast titrates a 500 mL solution of 2 M C2H5OCOOH (lactic acid) with a 1 M KOH
solution for the sheer thrill of titration. What is the pH at the equivalence point at 25oC?
Structure of lactic acid:
Ka of lactic acid = 1.4 x 10¯
A.
B.
C.
D.
E.
8.8
10.1
9.1
3.9
12.1
4
---------------------------------------------------------------------------------------------------------------------------11. Which of the following slightly soluble salts would be substantially more soluble in an ACIDIC
aqueous solution than in pure water at 25oC?
i. Ca3(PO4)2 (s)
ii. Fe(OH)3 (s)
iii. AgBr (s)
iv. SrCO3 (s)
v. CuI (s)
A.
B.
C.
D.
E.
ii and v only.
ii and iv only.
iii, iv, and v only.
i, ii, and iv only.
All of these salts are more soluble in acidic solutions.
---------------------------------------------------------------------------------------------------------------------------12. What is the coefficient in front of water, and is it a product or reactant, when the following redox
reaction is balanced in acidic solution?
NO (g) + MnO4– (aq) → NO2– (aq) + MnO2 (s)
A.
B.
C.
D.
E.
1, reactant
1, product
2, reactant
2, product
3, reactant
---------------------------------------------------------------------------------------------------------------------------13. Put the following species in order from worst oxidizing agent to best oxidizing agent at 25oC:
i. H2O2 (aq)
ii. Li+ (aq)
iii. F– (aq)
A.
B.
C.
D.
E.
i < ii < iii
ii < i < iii
i < iii < ii
ii < iii < i
iii < i < ii
---------------------------------------------------------------------------------------------------------------------------14. What is the equilibrium constant constant, Keq, for the voltaic cell in the reaction below at 25oC?
Cu(NO3)2 (aq) + Zn (s) → Cu (s) + Zn(NO3)2 (aq)
–15
A. 4.0 x 10
B. 1.5 x 1037
C. 6.9 x 10–38
D. 2.0 x 109
E. 1.4 x 1016
------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------PLEASE USE THE FOLLOWING ELECTROCHEMICAL CELL DIAGRAM TO ANSWER THE
NEXT TWO QUESTIONS:
15. What is the Eocell of the voltaic cell pictured above at 25oC?
A.
B.
C.
D.
E.
+0.115 V
+0.559 V
+0.781 V
–0.107 V
–0.115 V
------------------------------------------------------------------------16. Which of the following actions would cause the cell potential (Ecell) of the voltaic cell pictured above
to INCREASE at 25oC?
i. Adding water to the anode.
ii. Adding water to the cathode.
iii. Increasing the [NaCl] to 2.0 M.
iv. Increasing [CuCl2] to 2.5 M.
v. Doubling the mass of the Ag (s) electrode.
A.
B.
C.
D.
E.
i and iii only.
ii and iv only.
i and ii only.
iii and iv only.
iv and v only.
------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------17. Rick T. Cat needs to make a fancy collar coated with platinum for his Nobel Prize acceptance speech!
He decides to utilize electrolysis to electroplate his existing collar (obviously!). How many grams of
platinum can be plated over a period of 1 hour if 1 amp of electrical current is used to electrolyze an
aqueous solution of PtCl2 at 25oC?
A.
B.
C.
D.
E.
7.28 g
3.64 g
0.10 g
10.94 g
2.25 g
---------------------------------------------------------------------------------------------------------------------------18. Which one of the following processes is the most spontaneous under standard conditions at 25oC?
A. The oxidation of Au (s)
B. The oxidation of Cl– (aq)
C. The oxidation of Na (s)
D. The oxidation of Al (s)
E. The oxidation of H2 (g)
---------------------------------------------------------------------------------------------------------------------------19. What is the pH of a saturated aqueous solution of Ca(OH)2 at 25oC? The Ksp of Ca(OH)2 (s) = 8.0 x
10¯6.
A.
B.
C.
D.
E.
12.1
1.9
12.4
1.6
5.1
---------------------------------------------------------------------------------------------------------------------------20. The data for the titration of a mystery acid with 1 M NaOH is given below. What is the approximate
Ka of this mystery acid?
A.
B.
C.
D.
E.
Ka = 4.6 x 10¯6
Ka = 1.4 x 10¯3
Ka = 3.7 x 10¯7
Ka = 8.0 x 10¯13
Ka = 1.8 x 10¯5
----------------------------------------------------------------------------------------------------------------------------
21. Place the following salts in order from lowest molar solubility to highest molar solubility in an
aqueous solution at 25oC:
i. BaF2 (s), Ksp = 1.7 x 10¯6
ii. CaSO4 (s), Ksp = 2.4 x 10¯5
iii. CoS (s), Ksp = 4.2 x 10¯8
A.
B.
C.
D.
E.
iii < i < ii
ii < i < iii
iii < ii < i
i < ii < iii
i < iii < ii
---------------------------------------------------------------------------------------------------------------------------22. Which one of the following mixtures would result in a buffer solution at 25oC?
A.
B.
C.
D.
E.
100 mL of 0.5 M HCl + 100 mL of 0.5 M NaOH
100 mL of 0.5 M NaF + 100 mL of 0.5 M HCl
50 mL of 0.5 M HF + 100 mL of 0.5 M NaOH
100 mL of 0.5 M HF + 50 mL of 0.5 M NaOH
100 mL of 0.5 M NaF + 50 mL of 0.5 M NaOH
---------------------------------------------------------------------------------------------------------------------------23. An aqueous solution contains a mixture of 0.05 M NaBr, 0.05 M NaF, and 0.05 M KCl. If 1.0 M
Pb(NO3)2 (aq) is added dropwise to this solution, what will be the FIRST solid to start precipitating at
25oC considering the Ksp values in the table below?
A.
B.
C.
D.
E.
Pb (s)
NaCl (s)
PbBr2 (s)
PbCl2 (s)
PbF2 (s)
Salt
Ksp
PbBr2 (s)
6.6 x 10–6
PbCl2 (s)
2.4 x 10–4
PbF2 (s)
4.0 x 10–8
---------------------------------------------------------------------------------------------------------------------------24. Consider the dissociation of Aspirin (acetylsalicylic acid) below. Which of the following will occur
upon the addition of NaOH(aq) to an aqueous solution of Aspirin at 25 oC?
i. Ka will increase.
ii. ∆G will decrease.
iii. pH will increase.
iv. The concentration of Aspirin will decrease.
v. The reaction will shift to the left.
A.
B.
C.
D.
E.
i and iv only
ii, iii, and iv only
iii and v only
i, iii, and v only
i, ii, and iv only
---------------------------------------------------------------------------------------------------------------------------25. What are the initial elemental products formed at the anode and cathode if an aqueous solution
containing 1M NaF (aq) is electrolyzed at 25oC?
Initial product
at the ANODE
Initial product at
the CATHODE
A.
F2 (g)
Na (s)
B.
O2 (g)
Na (s)
C.
H2 (g)
O2 (g)
D.
F2 (g)
H2 (g)
E.
O2 (g)
H2 (g)
------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------END OF EXAM
----------------------------------------------------------------------------------------------------------------------------
ANSWER KEY
1. E
2. A
3. C
4. E
5. C
6. C
7. D
8. C
9. A
10. A
11. D
12. A
13. D
14. B
15. A
16. D
17. B
18. C
19. C
20. E
21. C
22. D
23. E
24. B
25. E