- When a metal reacts with oxygen to form a metal oxide, a redox reaction occurs.Metal + Oxygen → Metal oxide
- In this reaction,
- Metal is oxidised to metal ions. The oxidation number of the metal increases.
- Oxygen is reduced to the oxide ion. The oxidation number of oxygen decreases from 0 to -2.
- Metal acts as a reducing agent while oxygen acts as an oxidising agent.
- Different metals burn in oxygen with different rate depending on their differing activeness.
- The more reactive metal towards oxygen, the brighter and faster the combustion of the metal.
- The arrangement of the metal according to the tendency of reaction with oxygen to form the metal oxide is known as the reactivity series of metals.
- Figure above shows the experiment is conduct to build the reactivity series of metal. Table below shows the result of the experiment.
| Metal | Observation |
| Magnesium | Combust quickly with a bright white shiny flame. A white powder is formed. |
| Zinc | A bright flame spread slowly. The powder produced is yellow when hot, and white when it is cold. |
| Iron | Embers spread slowly. A reddish brown powder is formed. |
| Lead | Red hot embers slowly. The powder produced is brown when hot, and yellow when it is cold. |
| Copper | Embers burn at a very slow rate. A black powder is formed. |
- Oxygen that is used in combustion of other metals is provides by heating solid potassium manganate(VII), also can be obtained from
- heating the mixture potassium chlorate (V) and manganese (IV) oxide (catalyst)2KClO3 (s) → 2KCl (s) + 3O2(g)
- heating potassium nitrate
2KNO3 (s) → 2KNO2 (s) + O2(g)