Question

What is the colour of ${\text{FeSO}}_4.7{\text{H}}_2\text{O}$ crystals? How does this colour change upon heating and what are the products formed?

Answer 1

Hydrated ferrous sulphate crystals are green in colour. On heating, single reactant breaks down to give simpler products. So, this is a decomposition reaction.
Ferrous sulphate crystals (${\text{FeSO}}_4.7{\text{H}}_2\text{O}$) lose water when heated and the colour of the crystals changes.
It then decomposes to ferric oxide (${\text{Fe}}_2{\text{O}}_3$), sulphur dioxide (${\text{SO}}_2$) and sulphur trioxide (${\text{SO}}_3$). Ferric oxide is a solid, while ${\text{SO}}_2$ and ${\text{SO}}_3$ are gases.