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C6: Oxidation and Reduction

Understand the terms oxidation and reduction in terms of the addition and removal of

oxygen

Although you may not be aware of it, we are all very familiar with one example of an oxidation

reaction. We have all left a toy, bike or car outside and when we return it has begun to rust. Rusting

is the oxidation of iron. The iron has gained oxygen to become iron oxide.

The substance has been oxidized as it has gained oxygen.

To get the iron back from the iron oxide we need to remove the oxygen from the compound. This can

be done by heating it strongly with carbon (more about that later). This type of reaction is known as a

reduction reaction.

The substance has been reduced as it has lost oxygen.

Be able to write simple equations to describe oxidation and reduction, using both words and

symbols

If magnesium is heated with copper oxide the magnesium will take the oxygen from the copper oxide.

This is an example of a displacement reaction.

Copy the below URl into you web browser to see an example of the

reaction between magnesium and copper (II) oxide.

http://www.youtube.com/watch?v=hcy2jwy5HUw

magnesium + copper (II) oxide magnesium oxide + copper

Mg (s) + Cu O (s) MgO (S) + Cu (s)

During this reaction the magnesium is oxidised and the copper is reduced.

The copper (II) oxide acts as an oxidising agent, it causes the magnesium to be oxidised.The magnesium is the reducing agent, it caused the copper to lose its oxygen.

We can also consider this equation in terms of electron transfer.

Mg (s) Mg2+ (s) + 2e-

Cu2+ (s) + 2e- Cu (s)

These equations are called half equations. They only show part in the reaction from the point of view

of part of the subsance that is reacting. From the half equation we can see that when the magnesium

is oxidised it loses electron and when the copper is reduced it gains electrons.

This can be remembered using:

OIL RIG

Oxidation Is Loss of electrons, Reduction Is Gain of electrons

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www.revise-physics.net Allan Riddick

Appreciate the role of carbon in the extraction of metals from their ores

The less reactive metals can be extracted from thier ores by heating then with either carbon or carbon

monoxide. During these reactions the carbon of carbon monoxide acts are an oxidizing agent and

removes the oxygen from the metal ore.

Iron ore:

iron (III) oxide + carbon monoxide iron + carbon dioxide

Fe2O3 (s) + 3 CO (g) 2 Fe (l) + 3 CO2 (g)

Copper ore:

copper (II) oxide + carbon copper + carbon dioxide

2 CuO (s) + C (s) 2 Cu (s) + CO2 (g)

The higher up the reactivity series the metal is the more energy is required to remove it from its ore.

Small amounts of copper can be obtained in the lab but few school have the equipment required to

heat iron ore sufficiently to obtain iron.