Oxidation and Reduction,
Electrochemistry
Charles H. Mahler
Pennsylvania Multi-Region STEM Grant
Immaculata University
July-August 2013
Oxidation State (number) Rules
1) Pure elements ox. states = zero
2) Simple ions ox. states = charge
3) H in compounds is usually +1
4) O in compounds is usually -2
5) Sum of all ox. states in molecules is
zero, in complex ions equals ion charge
6) Can use Periodic Table for other
simple ox. states (Na +1, F -1, Mg +2)
Daniell Cell: 1.10 volts
Zn(s) + Cu2+(aq) → Zn2+(aq) + Cu(s)
http://commons.wikimedia.org/wiki/File:Galvanic_cell_labeled.svg
If A and B are opened together, water will flow from B to A.
If A and C are opened together, water will flow from C to A.
If D and E are opened together, water will flow from E to D.
If F and B are opened together, water will flow from F to B.
Instead of figuring out their exact heights, or listing all possible combinations,
to predict the direction of flow all we need is to list these tanks by height:
(Highest) E > F > B > C > A > D (Lowest)
Figure taken from and examples adapted from http://bouman.chem.georgetown.edu/S02/lect25/lect25.htm
Standard Reduction Potentials
All written as reductions, listed in order from highest voltage to lowest
Table taken from http://bouman.chem.georgetown.edu/S02/lect25/lect25.htm
To make a cell, you need both
an oxidation and a reduction
The standard potential (voltage) for
a galvanic cell is just:
Eocell = Eoreduction- Eooxidation
Eocell = Eoreduction- Eooxidation
Zn(s) + Cu2+(aq) → Zn2+(aq) + Cu(s)
(aq) +
 Cu (s) 0.34 V
Zn2+ (aq) + 2e-  Zn (s) –0.76 V
2+
Cu
2e
Eocell = 0.34 V – (–0.76 V) = 1.10 V
Electrochemistry Vocabulary I
Galvanic cell – has a positive potential (voltage) and is a
spontaneous reaction, used to do electrical work / is a source
of energy (an example is a battery)
Anode – electrode where oxidation takes place in a galvanic
cell
Cathode - electrode where reduction takes place in a galvanic
cell
Electrochemistry Vocabulary II
Electrolytic cell - has a negative potential (voltage) and is NOT a
spontaneous reaction, consumes electrical work / needs an
outside source of energy to run (an example is a battery being
charged, or splitting water into hydrogen and oxygen)
Galvanized – a metal (usually iron or steel) that has a layer of
zinc (Zn) applied to prevent rusting has been galvanized. The zinc
will oxidize before the iron will, protecting the iron.
Rusting vs. Galvanized metal
Left image: http://commons.wikimedia.org/wiki/File:Rust_1.jpeg
Right image: http://commons.wikimedia.org/wiki/File:Feuerverzinkte_Oberfl%C3%A4che.jpg