Oxidation

In an oxidation reaction, as substance gains oxygen. Combustion is an example of an oxidation reaction

When a metal/non-metal reacts with oxygen, this is also an oxidation reaction.

Metals

When a metal reacts with oxygen, it produces a metal oxide. In the equation:

Metal + Oxygen ⮕ Metal oxide

Metal oxides are formed when metals react with oxygen. They are bases which react with acids and neutralise them. Some metal oxides dissolve in water to form alkaline solutions For example, magnesium reacts with oxygen to form magnesium oxide. The reaction is:

Magnesium + Oxygen ⮕ Magnesium oxide

Otherwise written as

2Mg + O2 ⮕ 2MgO

  • We use the numbers in front of the symbols to balance the equation
  • As oxygen comes in groups of two, written as O2, we add a 2 in front of magnesium (Mg) to make 2Mg + O2 ⮕ MgO
  • This also means we must place a 2 in front of magnesium oxide (MgO), to balance the equation 2Mg + O22MgO
  • The oxide comes from the oxygen (O)

For reactive metals, heat isn’t required for them to react with oxygen. When they are exposed to the air, they will react with oxygen in the air, which will develop an outer oxide later around the metal.

You will be able to see that the oxide layer has developed as it is often a different colour. A helpful feature of the oxide layer is how it prevents the metal from further reaction.

Metals Reacting with Oxygen under a Flame

With some less reactive metals require heat to react with oxygen.

  • For example, copper (which isn’t very reactive) forms a copper oxide layer, when placed over a Bunsen burner flame.

With more reactive metals, they produce a more vigorous reacted when heated over a Bunsen burner flame.

  • For example, burning magnesium in air produces intense heat and light. This forms magnesium oxide
  • So intense that you have to take precautions to avoid burns and eye damage

Another example is

Sodium + Oxygen ⮕ Sodium oxide

Otherwise written as

4Na + O2 ⮕ 2Na2O

Non-Metals

Non-metals react with oxygen to form non-metal oxides. For example, carbon reacts with oxygen to form carbon dioxide.

Another example is

Sulphur + Oxygen ⮕ Sulphur oxide

Otherwise written as

2S + O2 ⮕ 2SO