Topic 7: Oxidation, reduction and redox equations
Oxidation and reduction
Oxidation is loss of electrons. Reduction is gain of electrons.
Oxidation and reduction occur simultaneously in a reaction because one species loses
electrons which are then donated and gained by the other species. Therefore they are
known as redox reactions (reduction - oxidation).
This redox rule is remembered using the acronym OILRIG (oxidation is loss, reduction is
gain).
Oxidation number
Oxidation number gives the oxidation state of an element or ionic substance. Allocation of
oxidation number to a species follows a number of rules:
● Oxidation number of an element is zero.
● Oxidation numbers in a neutral compound add up to zero.
● Oxidation numbers in a charged compound add up to total the charge.
● Hydrogen has an oxidation number of +1.
● Oxygen has an oxidation number of -2.
● All halogens have an oxidation number of -1.
● Group I metals have an oxidation number of +1.
These rules can be used to work out the oxidation number of species or elements in a
reaction.
This compound must total zero, therefore using the rules above, the oxidation number of
Sulfur can be found.
2-8+x=0
-6 + x = 0
X=6
Oxidation and reduction
Oxidation is loss of electrons. Reduction is gain of electrons.
Oxidation and reduction occur simultaneously in a reaction because one species loses
electrons which are then donated and gained by the other species. Therefore they are
known as redox reactions (reduction - oxidation).
This redox rule is remembered using the acronym OILRIG (oxidation is loss, reduction is
gain).
Oxidation number
Oxidation number gives the oxidation state of an element or ionic substance. Allocation of
oxidation number to a species follows a number of rules:
● Oxidation number of an element is zero.
● Oxidation numbers in a neutral compound add up to zero.
● Oxidation numbers in a charged compound add up to total the charge.
● Hydrogen has an oxidation number of +1.
● Oxygen has an oxidation number of -2.
● All halogens have an oxidation number of -1.
● Group I metals have an oxidation number of +1.
These rules can be used to work out the oxidation number of species or elements in a
reaction.
This compound must total zero, therefore using the rules above, the oxidation number of
Sulfur can be found.
2-8+x=0
-6 + x = 0
X=6
