Page 1 of 4 OXIDATION AND REDUCTION
OXIDATION AND REDUCTION
1. OXIDATION: It is defined as a reaction in which:
- Oxygen is added to a substance.
- Hydrogen is removed from a substance.
- Electrons are lost by a substance.
AN OXIDIZING AGENT
It is substance which brings about oxidation; either by accepting electrons from a substance, transferring
oxygen to a substance or removing hydrogen from a substance.
Below are some common oxidizing agents:
- Oxygen ( )
- Chlorine ( )
- Manganese dioxide ( )
- Hot concentrated nitric acid ( )
- Hot concentrated sulphuric acid ( )
- Acidified potassium permanganate ( / )
- Acidified potassium dichromate ( / )
2. REDUCTION: It is defined as a reaction in which:
- Oxygen is removed from a substance.
- Hydrogen is added to a substance.
- Electrons are gained by a substance.
A REDUCING AGENT
It is substance which brings about reduction; either by donating electrons to a substance, removing oxygen
from a substance or adding hydrogen to a substance.
Below are some common reducing agents:
- Hydrogen
- Metals
- Carbon, usually in the form of coke or charcoal.
- Carbon monoxide ( )
- Hydrogen sulphide ( )
- Ammonia ( )
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Page 2 of 4 OXIDATION AND REDUCTION
REDOX REACTIONS
A redox reaction is one in which oxidation and reduction occur simultaneously i.e. occur at the same time.
Every oxidation is accompanied by a reduction and vice versa. In a redox reaction, the oxidizing agent is
reduced while the reducing agent is oxidized.
EXAMPLES OF REDOX REACTIONS
OXIDATION NUMBERS
An oxidation number is a number assigned to an element to show its state of oxidation or reduction.
RULES FOR ASSIGNING OXIDATION NUMBERS
1) All elements in the Free State (i.e. not combined with any other elements) have an oxidation number of
zero e.g. the oxidation number of Na, Fe, O , H , Cl , etc is zero.
2) In a simple ion, the oxidation number of the element concerned is the same size and sign as the charge
on the ion e.g.
Simple ion
Oxidation +2 -2 +1 -1
number
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Page 3 of 4 OXIDATION AND REDUCTION
3) In a polyatomic ion, the algebraic sum of all the oxidation numbers of the elements present is equal to
the size and sign of the charge on the ion.
4) The algebraic sum of all the oxidation numbers of the elements in a neutral compound is zero.
5) The oxidation number of hydrogen in all compounds is +1 except in metallic hydrides in which it is -1
while that of oxygen in all compounds is -2 except in peroxides in which it is -1.
EXAMPLES
Determine the oxidation number of:
i) Sulphur in
ii) Copper in
iii) Phosphorus in
iv) Chromium in
v) Manganese in
ASSIGNMENT
What is the oxidation number of?
a) Carbon in
b) Sulphur in
c) Phosphorus in
d) Manganese in
e) Nitrogen in
DEFINITIONS OF OXIDATION AND REDUCTION IN TERMS OF OXIDATION NUMBER
- Oxidation is an increase in oxidation number.
- Reduction is a decrease in oxidation number.
EXAMPLES
−2 →
1) ⟹
0 +2
+ →
2) ⟹
+3 +2
2 −2 →
3) ⟹
−1 0
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Page 4 of 4 OXIDATION AND REDUCTION
OXIDATION NUMBERS AND CHEMICAL NOMENCLATURE
When a compound contains an element with variable oxidation states, the oxidation number of the
element is included in the name of the compound. It is written as a Roman numeral in parenthesis after the
element’s name.
EXAMPLES:
= Sulphur (VI) oxide = Iron (II) chloride
= Sulphur (IV) oxide = Iron (III) chloride
= Phosphorus (III) chloride = Iron (III) oxide
= Phosphorus (V) chloride = Copper (I) oxide
= Carbon (IV) oxide = Copper (II) oxide
= Carbon (II) oxide = Copper (II) sulphate
ASSIGNMENT
1. Give the systematic names of the following compounds:
a) d) ( )
b) e) ( )
c) f)
2. State the oxidizing agent in each of the following reactions:
a) 2 ( )+ ( ) ⎯⎯⎯ 2 ( )+2 ( )+ ( )
b) 2 ( )+ ( ) ⎯⎯⎯ 2 ( )+3 ( )
3. State the reducing agent in each of the following reactions:
a) 2 ( )+3 ( ) ⎯⎯⎯ 3 ( )+3 ( )+ ( )
b) ( )+2 ( ) ⎯⎯⎯ ( )+2 ( )+ ( )
4. Consider the redox reaction below:
( )+4 ( ) ⎯⎯⎯ ( )+2 ( )+ ( )
Identify the substance that is:
a) Oxidized
b) Reduced
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