Oxidising and reducing agents

YOU SHOULD be able to:

■ Distinguish between oxidising and reducing agents.

■ Name common oxidising and reducing agents.

■ Identify the oxidising and reducing agents in a reaction using changes in oxidation number.

■ Perform tests for oxidising and reducing agents.

■ Investigate the action of common oxidising and reducing substances in everyday activities.

QUICK POINTS

Oxidation and reduction usually take place in a reaction through the action of oxidising and reducing agents. These redox reactions are often accompanied by colour changes. The oxidising agent is usually reduced in the reaction, while the reducing agent is usually oxidised in the reaction.

You can determine which substance is oxidised or reduced by tracking changes in the oxidation number.

EXAMPLE 1

The reducing agent (Pb) becomes oxidised – oxidation number increases from 0 to +2

The oxidising agent (NaNO ) becomes reduced – oxidation number of N decreases 3 from +5 to +3

EXAMPLE 2

The oxidising agent CuO supplies the oxygen. Cu changes from +2 to 0, so it is reduced. The reducing agent is hydrogen. It changes from 0 to +1, so it is oxidised.

EXAMPLE 3:

The reducing agent (Al) is the more reactive metal. The oxidation number of Al changes from 0 to +3, so it increases and is, therefore, oxidised.

The oxidising agent is Fe 2O3 as it is reduced. The oxidation number of Fe decreases from +3 to 0.

Common oxidising agents include aqueous chlorine, concentrated sulphuric acid, nitric acid, oxygen, hydrogen peroxide, acidified potassium manganate (VII), and potassium dichromate (VI) solutions.

Common reducing agents include carbon, carbon monoxide, hydrogen, hydrogen sulphide, metals, potassium iodide, and sulphur dioxide.