- Take about 2 g ferrous sulphate crystals in a dry boiling tube.
- Note the colour of the ferrous sulphate crystals. (Colour is green).
- Heat the boiling tube over the flame of a burner or spirit lamp as shown in Fig. 1.4.
- Observe the colour of the crystals after heating.
The green colour of ferrous sulphate (FeSO4. 7H2O) is changed to white due to the formation of anhydrous ferrous sulphate ((FeSO4). i.e., water is lost. On further heating, it becomes reddish-brown colour due to the decomposition of ferrous sulphate to ferric oxide (Fe2O3), sulphur dioxide (SO2) and sulphur trioxide (SO3) with a characteristic odour of burning sulphur.