Question

What is the color of ferrous sulphate crystals? How does this color change on heating ?

Answer 1

Ferrous sulphate crystals are light green in colour. They change to white on heating

 

$2FeSO_{4}(s) \rightarrow Fe_{2}O_{3}(s) + SO_{2}(g) + SO_{3}(g)$

Ahydrous ferrous   Ferric oxide

Sulphate (white)     (brown)

Ferrous sulphate crystals contain water molecules (FeSO₄. 7H₂O). On heating they lose water and anhydrous ferrous sulphate (FeSO₄) is formed. So their colour changes from light green to white. On further heating, anhydrous ferrous sulphate decomposes to form ferric oxide (Fe₂O₃), sulphur dioxide (SO₂) and sulphur trioxide (SO₃). So, the gas emitted smells like burning sulphur. So, the reaction is a decomposition reaction.