AP chem
Text: chapters 17
•
•
o
E =E
o
ox
+E
ΔG = -nFE
o
Review - 13
(Electrochemistry)
red
Choose the answer that best relates to
questions 1-4.
(A) there is no change in the voltage
(B) the voltage becomes zero
(C) the voltage increases
(D) the voltage decreases, but stays
positive
(E) the voltage becomes negative
1.
What happens to the voltage when a
saturated ZnSO4 solution is added to
the zinc compartment of the cell?
2.
What happens to the cell voltage
when the copper electrode is made
smaller?
What happens to the cell voltage
when the salt bridge is filled with
deionized water instead of 1 M
KNO3?
4.
What happens to the cell voltage
after the cell has operated for 10
minutes?
5.
MnO4 (aq) + H (aq) + C2O4 (aq) →
2+
Mn (aq) + H2O(l) + CO2(g). What is
+
the coefficient of H when the above
reaction is balanced?
(A) 16
(B) 2
(C) 8
(D) 5
(E) 32
6.
7.
-
2-
+
-
o
2-
2-
-
S2O3 + OH → SO4 + H2O + e .
After the above half-reaction is
balanced, which of the following are
the respective coefficients of OH
2and SO4 ?
(A) 8 and 3
(B) 6 and 2
(C) 10 and 2
(D) 5 and 2
(E) 5 and 1
How many moles of Pt may be
deposited on the cathode when 0.80
F of electricity is passed through a
4+
1.0 M solution of Pt ?
(A) 1.0 mol
(B) 0.60 mol
(C) 0.20 mol
(D) 0.80 mol
(E) 0.40 mol
o
E = E – (RT/nF)lnQ = E – (0.0592/n)logQ
o
log K = nE / 0.0592
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•
o
PROBLEMS
The following takes place in a voltaic cell:
2+
2+
Zn(s) + Cu (1 M) → Cu(s) + Zn (1 M).
The cell has a voltage of +1.10 V.
3.
Name: ____________________
8.
All of the following may serve as
reducing agents, EXCEPT:
(A) Mg
(B) Cs
2+
(C) Fe
(D) MnO4
(E) Br
9.
Cr2O7 + 14H + 3S → 2Cr + 3S
+ 7H2O. For the above reaction,
pick the true statement from the
following.
22(A) The S is reduced by Cr2O7 .
(B) The oxidation number of
chromium changes from +7 to
+3.
(C) The oxidation number of sulfur
remains -2.
22(D) The S is oxidized by Cr2O7 .
+
(E) The H oxidizes the S.
2-
+
+
-
2-
3+
-
10. H + NO3 + e → NO + H2O. What
is the coefficient for water arising
when the above half-reaction is
balanced?
(A) 3
(B) 4
(C) 2
(D) 1
(E) 6
2+
-
o
11. Co + 2e → Co, E = -0.28 V
2+
o
Cd + 2e → Cd, E = -0.40 V
Given the above standard reduction
potentials, estimate the approximate
value of the equilibrium constant for
the following reaction:
2+
2+
Cd + Co ⇌ Co + Cd
-4
(A) 10
-2
(B) 10
4
(C) 10
16
(D) 10
2
(E) 10
12. When a basic solution of KMnO4 is
added to an SnCl2 solution, a brown
4+
precipitate of MnO2 forms and Sn
remains in solution. When the same
basic solution of KMnO4 is added to
an NaF solution, no reaction occurs.
Which of the substances involved in
these reactions served as the
reducing agent?
(A) SnCl2
(B) KMnO4
(C) NaF
(D) MnO2
4+
(E) Sn
13. A sample of silver is to be purified by
electrorefining. This will separate
the silver from an impurity of gold.
The impure silver is made into an
electrode. Which of the following is
the best way to set up the
electrolytic cell?
(A) an impure silver cathode and an
inert anode
(B) an impure silver cathode and a
a pure gold anode
(C) A pure silver cathode with an
impure silver anode
(D) A pure gold cathode with an
impure silver anode
(E) An impure silver cathode with a
pure silver anode
-
+
2-
2+
14. 2MnO4 + 16H + 5S → 2Mn + 5S
+ 8H2O. The reducing agent in the
above reaction is which of the
following?
(A) MnO4
+
(B) H
(C) S
2(D) S
2+
(E) Mn
3+
2+
2+
15. 2Fe + Zn → Zn + 2Fe . The
reaction shown above was used in
an electrolytic cell. The voltage
measured for the cell was not equal
o
to the calculated E for the cell. This
discrepancy could be caused by
which of the following?
(A) The anion in the anode
compartment was chloride,
instead of nitrate as in the
cathode compartment.
(B) One or more of the ion
concentrations was not 1 M.
(C) One or more of the ion
o
concentrations were at 25 C
o
instead of 0 C.
(D) The solution in the salt bridge
was Na2SO4 instead of KNO3.
(E) The anode and cathode were
different sizes.
16. How many grams of mercury could
be produced by electrolyzing 1.0 M
Hg(NO3)2 solution with a current of
2.00 A for 3.00 h?
(A) 22.4 g
(B) 201 g
(C) 11.2 g
(D) 44.8 g
(E) 6.00 g
17. An electrolysis cell was constructed
with two platinum electrodes in a
1.00 M aqueous solution of KCl. An
odorless gas evolves from one
electrode, and a gas with a
distinctive odor evolves from the
other electrode. Choose the correct
statement from the following list.
(A) The gas with the distinctive odor
was evolved at the anode
(B) The odorless gas was oxygen.
(C) The gas with the distinctive odor
was evolved at the negative
electrode.
(D) The odorless gas was evolved
at the positive electrode.
(E) The odorless gas was evolved
at the anode.
18. H2O2(aq) + KIO4(aq) → KIO3(aq) +
O2(g) + H2O(l). Choose the true
statement from the following list:
(A) The iodine oxidation state is
reduced from +8 to +6.
(B) This is not an oxidationreduction reaction.
(C) H2O2 behaves as a reducing
agent.
(D) Hydrogen is reduced from +2 to
+1.
(E) H2O2 behaves as an oxidizing
agent.
-
19. Based on the reaction 2BrO3 + 12H
+ 10e → Br2 + 6H2O, choose the
correct statement:
(A) The BrO3 undergoes oxidation
at the anode.
(B) Br goes from a -1 oxidation
state to a 0 oxidation state.
(C) Br2 is oxidized at the anode.
+
(D) H is a catalyst.
(E) The BrO3 undergoes reduction
at the cathode.
1.
2.
3.
4.
5.
6.
7.
8.
9.
10.
11.
12.
13.
14.
15.
16.
17.
18.
19.
20.
21.
22.
23.
24.
25.
26.
D
A
B
D
A
C
C
D
D
C
C
A
C
D
B
A
A
C
E
B
E
B
D
D
D
D
+
-
20. Based on the reaction 2BrO3 + 12H
+ 10e → Br2 + 6H2O, if a current of
5.0 A is passed through the
electrolytic cell for 0.50 h, how
should you calculate the number of
grams of Br2 that will form?
!.! !.!" !"## (!"#.!)
(A)
(B)
(C)
(D)
(E)
(!")
!.! !.!" !"## (!"#.!)
!",!"" (!")
!.! !.!" !"## (!".!)
!",!"" (!")
!.! !.!" (!"#.!)
!",!"" (!")
3+
(C) pure copper
(D) impure copper
(E) impure copper
impure Cu
pure copper
pure zinc
24. Which of the following is true
regarding the reaction represented
below?
H2Se + 4O2F2 → SeF6 + 2HF + 4O2
!",!"" (!")
!.! !.!" !" (!"#.!)
2+
+
o
21. 2M + 3Zn →2M +3Zn E =0.90 V
2+
o
Zn + 2e → Zn, E = -0.76 V
3+
o
M + 3e → M, E = ??? V
Using the above information to
determine the missing standard
reduction potential.
(A) 0.90 V
(B) +1.66 V
(C) 0.00 V
(D) -0.62 V
(E) -1.66 V
22. In the electroplating of nickel, 0.200
faraday of electrical charge is
passed through a solution of NiSO4.
What mass of nickel is deposited?
(A) 2.94 g
(B) 5.87 g
(C) 11.7 g
(D) 58.7 g
(E) 294 g
23. If a copper sample containing some
zinc impurity is to be purified by
electrolysis, the anode and the
cathode must be which of the
following?
Anode
Cathode
(A) pure copper
pure zinc
(B) pure zinc
pure copper
(A) The oxidation number of O does
not change.
(B) The oxidation number of H
changes from -1 to +1.
(C) The oxidation number of F
changes from +1 to -1.
(D) The oxidation number of Se
changes from -2 to +6.
(E) This is a disproportionation
reaction for F.
25. When the equation below is
balanced using lowest wholenumber coefficients, the coefficient
+
for H is
2+
3+
Cr2O7 + H2S + H → Cr + S + H2O
(A) 2
(B) 4
(C) 6
(D) 8
(E) 14
26. What is Keq for the reaction:
2+
2+
Fe(s) + Ni → Fe + Ni(s) given:
2+
o
Ni + 2e → Ni E = -0.25 V
2+
o
Fe + 2e → Fe E = -0.44 V
-23
(A) 1.9 x 10
-8
(B) 7.6 x 10
3
(C) 3.6 x 10
6
(D) 2.6 x 10
22
(E) 5.2 x 10
FREE-RESPONSE QUESTIONS
27. A galvanic cell is construted with a cobalt electrode in a 1.0 M Co(NO3)2 solution in the left compartment, and a silver
electrode in a 1.0 M AgNO3 solution in the right compartment. The salt bridge contains KNO3(aq). The voltage is positive.
(A) What is the balanced net ionic equation for the reaction, and what is the cell potential?
27.
2+
o
Co + 2e → Co E = -0.28 V
a.Co(s) + 2Ag+(aq) → Co2+(aq) +
+
o
2Ag(s), E = +1.08 V
Ag + e → Ag
E = +0.80 V
b. cobalt
(B) Which electrode is the anode? Justify your answer.
c. KCl cannot be substituted because
(C) Could KCl be substituted for the KNO3 in the salt bridge? Justify your answer.
Cl- will precipitate to form AgCl
(D) If solid Co(NO3)2 is added to the cobalt compartment, what happens to the total voltage?
d. the voltage will decrease. Reaction
shifts left.
(E) If the cell is allowed to operate until equilibrium is established, what will the potential be?
e. At equilibrium, voltage will be 0 V.
28. The above galvanic cell is constructed with a cadmium electrode in a 1.0 M Cd(NO3)2 solution in the left compartment,
and silver electrode in a 1.0 M AgNO3 solution in the right compartment. The salt bridge contains KNO3(aq). The cell
2+
o
voltage is positive. (NOTE: Cd + 2e → Cd, E = -0.41 V)
(A) What is the balanced net ionic equation for the reaction, and what is the cell potential?
28.
(B) Show how to calculate the equilibrium constant for the cell.
a. 2Ag+ + Cd → Cd2+ + 2Ag, E = +1.21 V
b. log K = nEo/0.0592
(C) Write the expression for Q that would be needed in the Nernst equation.
c. Q = [Cd2+]/[Ag+]2
(D) Show how to calculate the free energy for the reaction.
d. ΔGo = -nFEo = (-2)(96,500)(1.21)
(E) Identify the anode, the cathode, the oxidizing agent, and the reducing agent.
e. anode = Cd, cathode = Ag, oxidizing
agent = Ag+, reducing agent = Cd