Activity . Take about g ferrous sulphate crystals in a dry boiling tube. Note the colour of the ferrous sulphate crystals. Heat the boiling tube over the flame of a burner or spirit lamp as shown in Fig.
. . Observe the colour of the crystals after heating. Have you noticed that the green colour of the ferrous sulphate crystals has changed?
You can also smell the characteristic odour of burning sulphur. 2FeSO (s) Heat Fe O (s) + SO (g) + SO (g) ( . ) (Ferrous sulphate) (Ferric oxide) In this reaction you can observe that a single reactant breaks down to give simpler products. This is a decomposition reaction.
Ferrous sulphate crystals (FeSO . 7H O) lose water when heated and the colour of the crystals changes. It then decomposes to ferric oxide (Fe O ), sulphur dioxide (SO ) and sulphur trioxide (SO ). Ferric oxide is a solid, while SO and SO are gases.
Decomposition of calcium carbonate to calcium oxide and carbon dioxide on heating is an important decomposition reaction used in various industries. Calcium oxide is called lime or quick lime. It has many uses – one is in the manufacture of cement. When a decomposition reaction is carried out by heating, it is called thermal decomposition.
CaCO (s) Heat CaO(s) + CO (g) ( . ) (Limestone) (Quick lime) Another example of a thermal decomposition reaction is given in Activity . .