Unit 7: Redox
Cell Potentials
What is going on in the Copper Lab?
What did you observe at the
pencil that was connected to the
red + terminal?
Orange/brown stuff collected on
the pencil
What did you observe at the pencil
that was connected to the black terminal?
Bubbles, smell of chlorine.
The Electrochemical Cell
Source:
www.battterybot.com
Source:
http://www.reuk.co.uk
Alkaline Battery
Lead-Acid (car)
Battery
The Electrochemical Cell

The species being oxidized LOSES electrons
 Occurs at the anode (both start with vowels!)
 Is the reducing agent
 Is the more active metal

Will go from metal to ion, thus putting out electrons
The Electrochemical Cell

The species being reduced GAINS electrons
 Occurs at the cathode (both start with
consonants!)
 Is the oxidizing agent
 Is the less active metal

Will go from ion to metal, thus taking in electrons
The Electrochemical Cell
Cu2+ + Zn → Zn2+ + Cu
1.
2.
3.
Zinc
Copper
4.
5.
ZnSO4
CuSO4
6.
Write the oxidation halfreaction
Write the reduction halfreaction
What is the oxidizing
agent?
What is the reducing
agent?
Where is the cathode?
Where is the anode?
Image: http://commons.wikimedia.org/wiki/File:Galvanic_cell_unlabeled.svg
The Electrochemical Cell
Cu2+ + Zn → Zn2+ + Cu
1.
2.
3.
4.
5.
6.
Write the oxidation halfreaction
Write the reduction halfreaction
What is the oxidizing
agent?
What is the reducing
agent?
Where is the cathode?
Where is the anode?
The Electrochemical Cell
Cu2+ + Zn → Zn2+ + Cu
How can we determine the
voltage (the cell potential)
created by an electrochemical
cell?
Zinc
Copper
Electrons flow from anode to
cathode. We can measure
this.
ZnSO4
CuSO4
Image: http://commons.wikimedia.org/wiki/File:Galvanic_cell_unlabeled.svg
Determining Cell Potentials
1.
Write the oxidation and reduction half-reactions
2.
Use the standard reduction table to determine:
Ecell = Eoreduction + Eooxidation
*Remember to flip the sign if you flip the half-reaction!
Cell Potential Example
Example:
Determine the standard reduction potentials and say if
the reaction is spontaneous as written:
Mn2+ + 4H2O + Sn2+ → MnO4- + 8H+ + Sn