Transcript Slide 1

General Chemistry
Principles & Modern Applications
9th Edition
Petrucci/Harwood/Herring/Madura
Chapter 20
Electrochemistry
Dr. Travis D. Fridgen
Memorial University of Newfoundland
© 2007 Pearson Education
What is the oxidation state of Cr in
Cr2O72- ?
1. +8
2. +7
3. +6
4. -1
5. -2
potassium dichromate
What is the oxidation state of Cr in
Cr2O72- ?
1. +8
2. +7
3. +6
4. -1
5. -2
potassium dichromate
When a piece of copper metal is put into a solution of
silver nitrate (AgNO3), silver metal is produced along
with Cu2+, the latter of which is responsible for the blue
color of the solution. Which of the following statements
is false?
1. DG for the reaction is negative (the reaction is
exergonic).
2. For every mole of Cu reacted, two moles of Ag is
produced.
3. Cu is oxidized.
4. Ag is an oxidizing agent.
5. A solution of CuSO4 will be blue.
When a piece of copper metal is put into a solution of
silver nitrate (AgNO3), silver metal is produced along
with Cu2+, the latter of which is responsible for the blue
color of the solution. Which of the following statements
is false?
1. DG for the reaction is negative (the reaction is
exergonic).
2. For every mole of Cu reacted, two moles of Ag is
produced.
3. Cu is oxidized.
4. Ag is an oxidizing agent.
5. A solution of CuSO4 will be blue.
For the electrochemical cell depicted to the
right, which of the following is correct the
shorthand notation?
Pb(s)
Pb(s), PbI2(s)
1. Pb(s) Pb + (1.8  104 M) I  (0.25 M) Pb(s)
2. Pb(s) Pb 2+ (1.8  104 M) I  (0.25 M) Pb(s),PbI 2 (s)
3. Pb(s) Pb+ (1.8  104 M) I  (0.25 M) Pb(s),PbI 2 (s)
4

4. Pb(s) Pb (1.8  10 M) I (0.25 M) PbI 2 (s)
2+
1.8 x 10-4 M
Pb(NO3)2
0.25 M KI
For the electrochemical cell depicted to the
right, which of the following is correct the
shorthand notation?
Pb(s)
Pb(s), PbI2(s)
1. Pb(s) Pb + (1.8  104 M) I  (0.25 M) Pb(s)
2. Pb(s) Pb2+ (1.8  104 M) I  (0.25 M) Pb(s),PbI 2 (s)
3. Pb(s) Pb+ (1.8  104 M) I  (0.25 M) Pb(s),PbI 2 (s)
4

4. Pb(s) Pb (1.8  10 M) I (0.25 M) PbI 2 (s)
2+
1.8 x 10-4 M
Pb(NO3)2
0.25 M KI
Given the following standard electrode potentials,
Ag + (aq) + e 
Fe 2+ (aq) + 2e 
E o = 0.80 V
Ag(s)
E o =  0.44 V
Fe(s)
N 2 (g) + 5H + (aq) + 4e 
N 2 H 5+ (aq)
E o =  0.23 V
Which of the following is spontaneous?
1. N2 (g) + 2Fe(s) + 5H+ (aq)
N2 H5+ (aq) + 2Fe2+
2. N2 (g) + 4Ag(s) + 5H+ (aq)
N2H5+ (aq) + 4Ag+
3. Fe2+ + 2Ag(s)
2Ag+ (aq) + Fe(s)
4. None of the above are spontaneous.
Given the following standard electrode potentials,
Ag + (aq) + e 
Fe 2+ (aq) + 2e 
E o = 0.80 V
Ag(s)
E o =  0.44 V
Fe(s)
N 2 (g) + 5H + (aq) + 4e 
N 2 H 5+ (aq)
E o =  0.23 V
Which of the following is spontaneous?
1. N2 (g) + 2Fe(s) + 5H+ (aq)
N2 H5+ (aq) + 2Fe2+
2. N 2 (g) + 4Ag(s) + 5H + (aq)
N 2 H 5+ (aq) + 4Ag+
3. Fe2+ + 2Ag(s)
2Ag+ (aq) + Fe(s)
4. None of the above are spontaneous.
A voltaic cell was produced based on the following overall reaction.
Zn2+ (aq) + Cu(s)
Cu2+ (aq) + Zn(s)
The emf was measured to be 0.21 V. Eocell
is -1.10 V. Which of the following three
statements is false?
Cu
Zn
1. When [Zn2+] and [Cu2+] = 1.00 M DG > 0
2. [Cu2+] must be far greater than [Zn2+]
3. DG < 0 for this cell but DGo > 0.
CuSO4(aq)
Zn(NO3)2(aq)
A voltaic cell was produced based on the following overall reaction.
Zn2+ (aq) + Cu(s)
Cu2+ (aq) + Zn(s)
The emf was measured to be 0.21 V. Eocell
is -1.10 V. Which of the following three
statements is false?
Cu
Zn
1. When [Zn2+] and [Cu2+] = 1.00 M DG > 0
2. [Cu2+] must be far greater than [Zn2+]
3. DG < 0 for this cell but DGo > 0.
CuSO4(aq)
Zn(NO3)2(aq)
Given the two electrochemical
cells to the right, a cell
constructed according to the
following shorthand notation
Zn(s) Zn 2+ (1 M) Cu 2 (1 M) Cu(s)
has a cell potential of:
1. 1.103
3. -0.423
2. 0.423
4. -1.103
Given the two electrochemical
cells to the right, a cell
constructed according to the
following shorthand notation
Zn(s) Zn 2+ (1 M) Cu 2 (1 M) Cu(s)
has a cell potential of:
1. 1.103
3. -0.423
2. 0.423
4. -1.103
Given the electrochemical cells to the
right, what would be the cell potential for
the electrochemical cell constructed as
indicated by the following shorthand
notation?
Zn(s) Zn 2+ (1 M) Ag  (1 M) Ag(s)
1. 2.023
2. 1.563
3. 0.643
4. -0.643
5. -1.563
Given the electrochemical cells to the
right, what would be the cell potential for
the electrochemical cell constructed as
indicated by the following shorthand
notation?
Zn(s) Zn 2+ (1 M) Ag  (1 M) Ag(s)
1. 2.023
2. 1.563
3. 0.643
4. -0.643
5. -1.563
Which of the following would result
in an increase in the cell potential?
1. Decreasing [Ag+] in the cathode.
2. Decreasing [Fe2+] in the anode.
3. Decreasing [Fe3+] in the anode.
4. Adding NaCl to the cathode.
5. Increasing [KNO3] in the salt bridge.
Which of the following would result
in an increase in the cell potential?
1. Decreasing [Ag+] in the cathode.
2. Decreasing [Fe2+] in the anode.
3. Decreasing [Fe3+] in the anode.
4. Adding NaCl to the cathode.
5. Increasing [KNO3] in the salt bridge.
Which of the following is false for the
electrolysis of water?
1. Water is oxidized to form oxygen at
the anode.
2. Water is reduced to form hydrogen at the
cathode.
3. The electrode marked A is the cathode and
that marked B is the anode.
4. The hydrolysis of water is non-spontaneous
and requires the input of energy from an
external source.
A
B
Which of the following is false for the
electrolysis of water?
1. Water is oxidized to form oxygen at
the anode.
2. Water is reduced to form hydrogen at the
cathode.
3. The electrode marked A is the cathode and
that marked B is the anode.
4. The hydrolysis of water is non-spontaneous
and requires the input of energy from an
external source.
A
B
When pure iron is put into pure water, it produces H2 gas, and when pure iron is
put into an acidic solution it produces H2 gas. Using the data below, state
whether the above statement is true or false.
O2 (g) + 4H + (aq) + 4e 
H 2O(l)
E o = 1.24 V
2H + (aq) + 2e 
H 2 (g)
E o = 0.00 V
Fe2+ (aq) + 2e 
Fe(s)
E o =  0.44 V
2H 2O(l) + 2e 
H 2 (g) + OH  (aq)
E o =  0.83 V
1. True
2. False
When pure iron is put into pure water, it produces H2 gas, and when pure iron is
put into an acidic solution it produces H2 gas. Using the data below, state
whether the above statement is true or false.
O2 (g) + 4H + (aq) + 4e 
H 2O(l)
E o = 1.24 V
2H + (aq) + 2e 
H 2 (g)
E o = 0.00 V
Fe2+ (aq) + 2e 
Fe(s)
E o =  0.44 V
2H 2O(l) + 2e 
H 2 (g) + OH  (aq)
E o =  0.83 V
1. True
2. False
Ecell
The Nernst equation for the electrochemical
cell depicted to the right is:
1. Ecell
0.0592 V
[Pb2+ ]3
= 1.551 V 
log
6
[Al3+ ]2
KNO3
Pb
2. Ecell
0.0592 V
[Al3+ ]
= 1.551 V 
log
3
[Pb2+ ]
3. Ecell
0.0592 V
[Al3+ ]2
=  1.551 V 
log
6
[Pb2+ ]3
4. Ecell =  1.551 V 
2+ 2
0.0592 V
[Pb ]
log
2
[Al3+ ]3
Al
Pb(NO3)2 (0.1M)
Al(NO3)3 (0.5M)
Pb2+ (aq) + 2e
Pb(s)
E o =  0.125 V
Al3+ (aq) + 3e
Al(s)
Eo =  1.676 V
Ecell
The Nernst equation for the electrochemical
cell depicted to the right is:
1. Ecell
0.0592 V
[Pb2+ ]3
= 1.551 V 
log
6
[Al3+ ]2
KNO3
Pb
2. Ecell
0.0592 V
[Al3+ ]
= 1.551 V 
log
3
[Pb2+ ]
3. Ecell
0.0592 V
[Al3+ ]2
=  1.551 V 
log
6
[Pb2+ ]3
4. Ecell =  1.551 V 
2+ 2
0.0592 V
[Pb ]
log
2
[Al3+ ]3
Al
Pb(NO3)2 (0.1M)
Al(NO3)3 (0.5M)
Pb2+ (aq) + 2e
Pb(s)
E o =  0.125 V
Al3+ (aq) + 3e
Al(s)
Eo =  1.676 V
In the electrochemical cell to the right the
concentrations of Mn2+ and Cr3+ are 0.010
M and 0.10 M, respectively. What is the
cell potential? Use the equation to the right
and do not use a calculator. Do use a pen
and paper!
E cell = 0.44 V 
0.06 V
log Q
n
KNO3
Cr
Mn
1. 0.48 V
2. 0.45 V
2. 0.44 V
4. 0.43 V
5. 0.40 V
Cr(NO3)3
Mn 2+ (aq) + 2e
Cr 3+ (aq) + 3e
Mn(NO3)2
Mn(s)
Cr(s)
E o =  1.18 V
E o =  0.74 V
In the electrochemical cell to the right the
concentrations of Mn2+ and Cr3+ are 0.010
M and 0.10 M, respectively. What is the
cell potential? Use the equation to the
right and do not use a calculator. Do use a
pen and paper!
E cell = 0.44 V 
0.06 V
log Q
n
KNO3
Cr
Mn
1. 0.48 V
2. 0.45 V
2. 0.44 V
4. 0.43 V
5. 0.40 V
Cr(NO3)3
Mn 2+ (aq) + 2e
Cr 3+ (aq) + 3e
Mn(NO3)2
Mn(s)
Cr(s)
E o =  1.18 V
E o =  0.74 V
Which of the following would be produced in
the largest abundance by mass by the
consumption of 1 kW hour of electricity?
1. Ni from a solution of Ni3+
10
11
12
2. Cu from a solution of Cu+
28
29
30
Ni
Cu
Zn
58.69
63.456
65.39
47
48
Ag
Cd
107.868
112.411
3. Zn from a solution of Zn2+
4. Ag from a solution of Ag+
5. Cd from a solution of Cd2+
Which of the following would be produced in
the largest abundance by mass by the
consumption of 1 kW hour of electricity?
1. Ni from a solution of Ni3+
10
11
12
2. Cu from a solution of Cu+
28
29
30
Ni
Cu
Zn
58.69
63.456
65.39
47
48
Ag
Cd
107.868
112.411
3. Zn from a solution of Zn2+
4. Ag from a solution of Ag+
5. Cd from a solution of Cd2+