Question

Ferrous sulphate decomposes with the evolution of a gas having a characteristic odour of burning Sulphur. Write the chemical reaction involved and identify the type of reaction.

Answer 1

Decomposition reaction:

• Decomposition reactions are the process in which chemical species break up into simpler parts
• These reactions often involve an energy source such as heat, light, or electricity that breaks apart the bonds of compounds.
• The general equation for Decomposition reaction is $\mathrm{AB}\to \mathrm{A}+\mathrm{B}$

Ferrous sulfate Decomposition reaction:

• Ferrous sulphate decomposes when gets heated and it forms a gas with sulphur in it.
• It is an endothermic reaction as it involves the absorption of heat.
• Ferrous sulphate crystals are in green colour and contain water molecules (${\mathrm{FeSO}}_4.7{\mathrm{H}}_2\mathrm{O}$).
• On heating, the Ferrous sulphate crystals lose the water and anhydrous Ferrous sulphate (${\mathrm{FeSO}}_4$) is formed and the colour changes from light green to white.
• On further heating, anhydrous Ferrous sulphate decomposes to form Ferric oxide (${\mathrm{Fe}}_2{\mathrm{O}}_3$), Sulphur dioxide(${\mathrm{SO}}_2$) and Sulphur trioxide (${\mathrm{SO}}_3$), the emitted gas has a characteristic odour of burning Sulphur.
• The single reactant ${\mathrm{FeSO}}_4$ decomposes to form three different products, therefore the reaction is a decomposition reaction.
  $\underset{\mathrm{Ferrous}\mathrm{sulphate}}{2{\mathrm{FeSO}}_4\left(\mathrm{s}\right)}\stackrel{∆}{\to }\underset{\mathrm{Ferric}\mathrm{oxide}}{{\mathrm{Fe}}_2{\mathrm{O}}_3\left(\mathrm{s}\right)}+\underset{\mathrm{Sulphur}\mathrm{dioxide}}{{\mathrm{SO}}_2\left(\mathrm{g}\right)}+\underset{\mathrm{Sulphur}\mathrm{trioxide}}{{\mathrm{SO}}_3\left(\mathrm{g}\right)}$

Therefore, Ferrous sulphate undergoes the decomposition reaction, that is $\underset{\mathrm{Ferrous}\mathrm{sulphate}}{2{\mathrm{FeSO}}_4\left(\mathrm{s}\right)}\stackrel{∆}{\to }\underset{\mathrm{Ferric}\mathrm{oxide}}{{\mathrm{Fe}}_2{\mathrm{O}}_3\left(\mathrm{s}\right)}+\underset{\mathrm{Sulphur}\mathrm{dioxide}}{{\mathrm{SO}}_2\left(\mathrm{g}\right)}+\underset{\mathrm{Sulphur}\mathrm{trioxide}}{{\mathrm{SO}}_3\left(\mathrm{g}\right)}$