Question

For $2$g of ferrous sulphate crystals are heated in a dry boiling tube.
(i) List any two observations
(ii) Name the type of chemical reaction taking place.
(iii) Write the chemical equation of the reaction.

Answer 1

Hint: Ferrous sulphate is a mineral that is required by the human body. Iron deficiency anaemia is treated with ferrous sulfate. Ferrous sulphate is primarily used in industry as a precursor to other iron compounds. Since it is a reducing agent, it can be used to convert chromate in cement to less volatile ${\text{Cr}}\left( {{\text{III}}} \right)$ compounds.

Complete answer:
The blue-green heptahydrate (hydrate with seven molecules of water), also known as copperas and green vitriol (vitriol is an archaic term for sulphate), is the most common type of ferrous sulphate. All ferrous sulphates dissolve in water to form the same aquo compound, which is paramagnetic and has an octahedral molecular geometry.
Until heating, ferrous sulphate crystals are considered to be pale green in colour. When ferrous sulphate crystals are heated, they turn brown or reddish brown in colour.
(i) As ferrous sulphate crystals are heated, the following two observations occur:
(a) A change in state and colour occurs.
(b) During this process, a gas is generated.
(ii) It is a decomposition reaction since the compound (ferrous sulphate) decomposes into two or more substances.
(iii) The following is the chemical reaction equation.
\[{\text{2FeS}}{{\text{O}}_{\text{4}}}{\text{(s)}}\,\,{\text{ + }}\,\,{\text{Heat}}\,\, \to \,\,{\text{F}}{{\text{e}}_{\text{2}}}{{\text{O}}_{\text{3}}}\left( {\text{s}} \right)\,\,{\text{ + }}\,{\text{S}}{{\text{O}}_{\text{2}}}\left( {\text{g}} \right)\,\,{\text{ + }}\,\,{\text{S}}{{\text{O}}_{\text{3}}}\left( {\text{g}} \right)\]

Note:
Ferrous sulphate is a soil amendment for lowering the pH of a high alkaline soil so that plants can access the nutrients.
It is used to treat iron chlorosis in horticulture. While it does not work as quickly as ferric EDTA, its effects last longer.