Write the chemical equations for the reactions taking place when:
(a) Magnesium ribbon is burnt in presence of air.
(b) Sodium metal catches fire in contact with water.
(c) Steam is passed over hot aluminium.
(a) Almost all metals combine with oxygen present in air to form metal oxides:
Metal + Oxygen → Metal oxide
When magnesium (a metal) ribbon is burnt in the presence of air, it reacts with oxygen to form magnesium oxide (MgO2), the following reaction takes place:
2Mg + O2→ 2MgO2
(b) Sodium metal reacts violently with water. The reaction is so violent and exothermic that the evolved hydrogen immediately catches fire. The reaction is:
2Na + H2O → 2NaOH + H2 + heat energy
(c) Aluminium do not react either with cold or hot water. It reacts with steam to form the aluminium oxide (Al2O3) and hydrogen. The reaction is:
2Al + 3H2O → Al2O3 + 3H2