Redox

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Redox Electrochemical Cells
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Review
Oxidation loss of e- increase
in ox reducing
agent Reduction gain of e-
decrease in ox oxidizing
agent
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Voltaic Cell
An electrochemical cell in which chemical energy
is spontaneously changed to electrical energy
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Dry cell Alkaline battery Lead storage Fuel cells
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What does a voltaic cell consist of? Lets look
at a wet cell!
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Salt solutions of each metal
M2(aq)
M1(aq)
M1
X-(aq)
M2
X-(aq)
M stands for any metal and X- stands for an anion
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M2(aq)
M1(aq)
Reduction ½ rxns of each metal
M1
X-(aq)
M2
X-(aq)
Anode M1 e- ? M1
Cathode M2 e- ? M2
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Anode and Cathode

• OXIDATION occurs at the ANODE.
• REDuction occurs at the CAThode.

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Salt Bridge
K(aq) NO3-(aq)
M2(aq)
M1(aq)
M1
X-(aq)
M2
X-(aq)
Cathode M2 e- ? M2
Anode M1 ? M1 e-
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e- flow is from source of high
concentration to source of low
concentration
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e-
e-
K(aq) NO3-(aq)
M2(aq)
M1(aq)
M1
X-(aq)
M2
X-(aq)
Cathode M2 e- ? M2
Anode M1 ? M1 e-
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shorthand notation oxidation reduction M1
M1 M2 M2 anode ? cathode ? e- flow ?
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Reduction Potential The ease with which a
chemical species can be reduced
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Activity Series Table 21.1 pg 664 Standard
Reduction Potential Table 21.2 pg 674
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This is upside down compared to your book. You
must pay attention!
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e- ?
K(aq) NO3-(aq)
Cu2(aq)
Ni2(aq)
X-(aq)
Cu
Ni
X-(aq)
Cu2 2e- ? Cu E0red 0.34 V
Ni2 2e- ? Ni E0red -0.25 V
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An electrochemical cell is spontaneous
iff Oxidation-reduction occurs The Ered Eox gt
0
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• Cell potential (reduction potential of ½ cell
  in which reduction occurs) (reduction potential
  of ½ cell in which oxidation occurs)
• EOcell EOred EOred (of the oxidized)
• EOcell EOred - EOoxid

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e-
e-
K(aq) NO3-(aq)
Cu2(aq)
Ni2(aq)
X-(aq)
Cu
Ni
X-(aq)
Cu2 2e- ? Cu E0red 0.34 V reduction
cathode
Ni ? Ni2 2e- E0 0.25 V oxidation anode
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E0(V) Cu2 2e- ? Cu
0.34 Ni ? Ni2 2e-
0.25 Cu2 Ni ? Cu Ni2
0.59
EOcell EOred - EOoxid 0.34 - (-0.25) 0.59V
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Line Notation
ANODE CATHODE Ni(s)Ni2
(aq,1 M)Cu2(aq,1 M)Cu(s) oxidation
reduction
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e- ?
K(aq) NO3-(aq)
Al3(aq)
Ni2(aq)
X-(aq)
Al
Ni
X-(aq)
Which will Oxidize?
Al3 3e- ? Al E0 -1.66 V
Ni2 2e- ? Ni E0 -0.23 V
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e-
e-
K(aq) NO3-(aq)
Al3(aq)
H(aq)
X-(aq)
Al
Ni
X-(aq)
Al ? Al3 3e- E0 1.66 V oxidation anode
Ni2 2e- ? Ni E0 -0.23 V reduction
cathode
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E0(V) Al ? Al3 3e-
1.66 Ni2 2e- ? Ni
-0.23 2Al 3Ni 2 ? 3Ni 2Al3 1.43
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Line Notation
ANODE CATHODE Al(s) Al3(aq,
1 M) Ni2(aq, 1 M) Ni (s) oxidation
reduction
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Examine Zn/Cu Cell
Zn/Cu cell web site
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1 (a)Sketch the Ag/Ag Zn/Zn2 wet cell.
Show the direction of e- flow and the direction
of ion migration. (b)Calculate E0 for the cell.
(c)Give the line notation for the cell.
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e- ?
K(aq) NO3-(aq)
Zn2(aq)
Ag(aq)
X-(aq)
Zn
Ag
X-(aq)
Zn2 2e- ? Zn E0 - 0.76 V
Ag e- ? Ag E0 0.80 V
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• EO 0.80 - (-0.76) 1.56V
• or
• Ag e- ? Ag 0.80V
• Zn ? Zn2 2e- 0.76V
• EOcell 1.56V
• Zn (s) Zn2 (aq) Ag (aq) Ag (s)