AQA A Level chemistry - AS Unit 2: Section 3.2.4 Redox Reactions

3.2.4 Redox Reactions - Oxidation and reduction

Students should:

know that oxidation is the process of electron loss
know that oxidising agents are electron acceptors
know that reduction is the process of electron gain
know that reducing agents are electron donors

Oxidation and reduction reactions

These are reactions where electrons are transferred from one species (atom, molecule or ion) to another. We can write 'half' equations to show only what happens to the species losing electrons or a different 'half' equation to show the species gaining electrons.

The whole equation is put together by making sure that the numbers of electrons are balanced in each half equation and adding them together (when the electrons will cancel out)

Oxidation

This is the name given to removal of electrons from a species - the reagent causing the loss of electrons is called the oxidising agent

Example:

Mg(s) Mg²⁺ + 2e

In this (half) equation the magnesium atom loses electrons and becomes an ion.

Reduction

This is the gain of electrons - the species donating the electrons is called the reducing agent

Example

Fe²⁺ + 2e Fe(s)

In this (half) equation the iron(II) ion gains two electrons to become an atom.

Redox reactions

Obviously the electrons leave one species and go to another. Consequently reduction has to be accompanied by oxidation and vice versa. For this reason reactions involving transfer of electrons are called reduction and oxidation or redox for short

Example

Mg(s) + Fe²⁺ Fe(s) + Mg²⁺

The electrons from the magnesium are transferred to the iron(III) ions

Summary

Loss of electrons = Oxidation

Gain of electrons = Reduction

The reducing agent provides the electrons and loses them itself - it gets oxidised.

The oxidising agent removes the electrons from the other species and gains them itself - it gets reduced.

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