Question

A green-colored hydrated metallic salt on heating loses its water of crystallization molecules and gives a suffocating smell. Identify the salt and write the chemical reaction.

Answer 1

Hydrated ferrous sulphate $({\mathrm{FeSO}}_4$$.7{\mathrm{H}}_2\mathrm{O})$ is a green-colored hydrated metallic salt that is on heating and loses its water of crystallization molecules and gives a suffocating smell. On heating, salt decomposes and gives a decomposition reaction.

Chemical reaction:

1. On slow heating: $\underset{\left(\mathrm{green}\right)}{{\mathrm{FeSO}}_4.7{\mathrm{H}}_2\mathrm{O}}\left(s\right)\stackrel{\mathrm{slow}\mathrm{heating}}{\to }{\mathrm{FeSO}}_4\left(\mathrm{s}\right)+7{\mathrm{H}}_2\mathrm{O}\left(\mathrm{l}\right)$
2. The hydrated ferrous salt loses its water of crystallization on slow heating and gives ferrous sulfate in solid form which is white in color. This confirms the presence of iron salt.
3. On strong heating: $2{\mathrm{FeSO}}_4\left(\mathrm{s}\right)\stackrel{\mathrm{strong}\mathrm{heating}}{\to }{\mathrm{Fe}}_2{\mathrm{O}}_3\left(\mathrm{s}\right)+{\mathrm{SO}}_2\left(\mathrm{g}\right)+{\mathrm{SO}}_3\left(\mathrm{g}\right)$.
4. On strong heating, ferrous sulfate gives brown-colored ferric oxide $\left({\mathrm{Fe}}_2{\mathrm{O}}_3\right)$ , sulphur dioxide(SO₂), and sulphur trioxide (SO₃).
5. Both $\mathit{(}S{O}_{2}andS{O}_3\mathit{)}$ gases cause suffocation on inhalation.

Hence, the salt will be hydrated ferrous sulphate.