Chemistry, Third edition

Oxidation and Reduction

Objectives

Defines oxidation, reduction and redox reaction

Explains how to work out oxidation numbers and write redox equations

Shows you how to use standard reduction potentials to decide if reactions

can occur

Discusses corrosion and redox reactions in nature

Redox reactions

Aredoxreaction is an important type of chemical reaction. In such a reaction, one

reactant is oxidizedand another reactant is reduced.

Definitions of oxidation and reduction

Oxidation was once regarded as a chemical reaction in which oxygen was added to a

substance, whereas reduction occurred when oxygen was lost.

For example, in the reaction

CO 2 (g)C(s)2CO(g)

carbon is oxidized to carbon monoxide (an atom of carbon gains an oxygen atom),

while carbon dioxide is reduced to carbon monoxide (a molecule of carbon dioxide

loses an atom of oxygen).

The definition was later broadened to include hydrogen: oxidation was removal

of hydrogen from a substance, while reduction took place when hydrogen was

added.

These definitions, however, do not help when oxygen and hydrogen are not

involved. Consider a reaction such as

Cu(s)S(s)CuS(s)

Oxygen and sulfur both have six electrons in the outer shell of their atoms and their

7.1

Contents

7.1Redox reactions 100

7.2Oxidation numbers 102

7.3Oxidizing and
reducing agents 104

7.4Writing and
balancing redox
equations 104

7.5Redox couples 107

7.6Activity series of
metals 113

7.7Corrosion of iron 114

7.8Redox reactions in
nature 115

7.8Revision questions 117

7

UNIT