Oxidation, Reduction and
Electrochemistry
 In this chapter you will be
exposed to some basic
concepts involved in a
special type of chemical
reaction.
 Time will not permit an indepth study of this, but the
main concepts will be
important to learn.
Oxidation-Reduction Reactions
 Oxidation-Reduction
reactions are also
termed Redox
reactions.
 A redox reaction is a
chemical reaction
which involves the loss
and gain of electrons.
Redox Reactions
 In a redox reaction one
substance is oxidized (loses
electrons) and another
substance is reduced (gains 2 Na(s) + Cl2(g)
2 NaCl
electrons)
 OIL RIG ( oxidation is
Na – loses 1 electron (oxidized)
loss, reduction is gain of
Cl – gains 1 electron (reduced)
electrons)
 LEO the lion goes GER
(loss of electrons is
oxidation, gain of electrons
is reduction.
Practice Problem
 Identify the substance oxidized and reduced in the
following redox equation.
 Ag (s) + NO3 (aq)
AgNO3
Oxidation Numbers
 To analyze an equation as a
redox reaction it’s essential
to identify the oxidation
numbers of the reactants
and products.
 Changes in oxidation
numbers reveal if a
substance is oxidized or
reduced.
Oxidation Number Rules

When assigning oxidation numbers use the following
rules:
1) The oxidation number for any “free” or uncombined
element in atomic or molecular form is 0.
2) The oxidation number of a monatomic ion is equal to the
charge on the ion.
3) The oxidation number of an atom of fluorine in a
compound is always –1 because it is the most
electronegative.
Oxidation Numbers
4) An atom of the more electronegative element in a binary
compound is assigned the number equal to its ion charge.
5) In compounds, atoms of group I, II, and aluminum have
positive oxidation numbers : +1, +2, +3 respectively.
6) Hydrogen is +1 unless combined with a metal atom, then
its –1.
7) The oxidation number of oxygen is usually –2. When
combined with fluorine it is +2. In peroxides, such as
H2O2 oxygen has the oxidation number –1.
Oxidation Numbers
8) The sum of the oxidation numbers of all atoms in a particle
must equal to zero in a compound and to its charge for a
polyatomic ion.
Oxidation Number Practice
 NH4+ :
 Al :
 BF3 :
 KClO3
 CO32-
Oxidation Number Practice
 NH4+ : H= +1
 Al : 0
N= -3
 BF3 : F=-1
B: +3
 KClO3
 CO32-
K=+1
O= -2
O= -2
C=+4
Cl= +5
Identifying Redox Reactions
 To identify a redox
reaction you must analyze
the oxidation numbers of
reactants and products.
Redox Reaction
Identify oxidized and reduced
substance:
1)
Cl2 + 2HBr  2HCl + Br2
0
+1 -1
+1 -1
0
Assign oxidation numbers to each atom in the
equation.
Consider only the atoms for which there was a
change in oxidation number.
Identify oxidized and reduced
substance:
1)
Cl2 + 2HBr  2HCl + Br2
0
+1 -1
+1 -1
0
An increase in oxidation number indicates an oxidation.
A decrease in oxidation number indicates a reduction.
The oxidation number of Cl decreased (from 0 to -1): Cl was
reduced
The oxidation number of Br increased (from -1 to 0): Br was
oxidized
Identify oxidized and reduced
substance:
2)
2H2 + O2  2H2O
0
0
+1 -2
An increase in oxidation number indicates an oxidation.
A decrease in oxidation number indicates a reduction.
The oxidation number of O decreased (from 0 to -2): O was
reduced
The oxidation number of H increased (from 0 to +1): H was
oxidized
Classwork
 Oxidizing and reducing handout