When a green iron salt is heated strongly, its colour finally changes to black and odour of burning sulphur is given out.
a. Name the iron salt.

b. Name the type of reaction that takes place during the heating of iron salt.

c. Write the balanced chemical equation for the reaction involved.

(a) The salt of iron which is green in colour is Iron [II] Sulphate. It occurs in hydrated form and its chemical formula is FeSO₄.7H₂O [Ferrous Sulphate Heptahydrate]. It is also commonly called green vitriol.

(b) According to the above-mentioned description, the reaction is a thermal decomposition reaction as ferrous sulphate decomposes to iron [III] oxide and oxides of sulphur [sulphur dioxide and sulphur trioxide] on heating. So the black colour mass obtained at the end of the reaction is Iron [III] oxide and the odour of the burning of sulphur is due to oxides of sulphur formed in the reaction.

(c) The reaction is as follows:

2FeSO₄→ Fe₂O₃ + SO₂ + SO₃