Redox Reactions
Chemical Reactions
There are 3 major classes of chemical reaction:
1. Precipitation
2. Acid-base
3. Redox

Oxidation


Refers to the gain of oxygen in a chemical
reaction
EXAMPLE:
Iron + oxygen
Iron(II) oxide
Write the chemical equation (unbalanced)
Fe + O2
FeO
The iron has gained oxygen and has been oxidised
Reduction


Is the opposite of oxidation
This means that it involves the lose of oxygen
Write a chemical equation for the reduction of
calcium oxide.
Balance the equation
2CaO
2Ca + O2
Redox reactions
Whenever a chemical is oxidised, another chemical
must be reduced, and vise vera
EXAMPLE:
Mg + CuO
MgO +
Cu
Write a similar equation for the reaction of zinc
and iron oxide.
Label the oxidation and reaction steps
Introducing electrons
Mg +
CuO
MgO +
Cu
The oxidation and reduction steps can be written
out separately:
OXIDATION
REDUCTION
Mg
2+O2CuO
Cu
MgO
Mg2+O2Cu
Re-write the above two steps, but add charges to
the ions involved
In the oxidation step:
Mg + O2
Mg2+O2The magnesium atoms have turned into
magnesium ions
Have they gained or lost electrons?
OXIDATION IS ALWAYS LOSS of electrons
O.I.L.
Where have the electrons gone to?
They have been taken by the copper:
Cu2+O2Cu
The copper has turned from ions into atoms
2+
+
2-
Cu2+
+
2e
NEUTRAL
Cu
REDUCTION IS ALWAYS GAIN of electrons
R.I.G.
Practice
Write similar ion-electron equations for:
Calcium ions turning into calcium atoms
Sodium ions turning into sodium atoms
Aluminium ions turning into aluminium atoms

All of these REDUCTIONS can be found in the data booklet
Potassium atoms turning into potassium ions
Nickel atoms turning into nickel(II) ions
Writing ion-electron equations


All reductions are found in data booklet
To write the oxidation, reverse the equation
Cu2+ + 2e
Cu
Cu
Cu2+ + 2e
Both sides of the equation should be neutral
when the charges are added together
 REMEMBER: OIL RIG

Problems
1.
(a)
(b)
(c)
2.
Look at the following equation:
Zn + Ag2O
ZnO + Ag
Which chemical is being oxidised?
Write an ion-electron equation for the
oxidation step.
Write an ion-electron equation for the
reduction step.
Assessment tests 10.3 and 10.4