Question

When a green iron salt is heated strongly, its colour finally changes to brown and the odour of burning sulphur is given out.
A.Name the iron salt.
B.Name the type of reaction that takes place during the heating of iron salt.
C.Write a chemical equation for the reaction involved.

Answer 1

Decomposition reaction is a reaction in which a compound decomposes to more than one compound in the presence of external energy sources. There are various physical and chemical properties that help to differentiate among the chemical compounds and one of such properties is the colour of the salt or the compound and the colour of their flames on burning help to differentiate the compound from others and also indicates the presence of certain elements in the compound.

Complete step by step answer:
Chemical compounds differ from each other in physical as well as in chemical properties. Certain compounds are soluble in water, some are not whereas some react with an element readily and some do not but a standard level of differentiation among the compounds is the colour of the salts or their flames when they burn. The different coloured salts or flames help to differ between compounds and also help to indicate the presence of certain elements or groups in a compound.

For the given question,
A.The iron salt which is green in colour changes to brown colour with a burning sulphur odour is ferrous sulphate with a molecular formula of $FeS{O_4}$.
B.When a green iron salt is heated to give brown colour compound then the type of reaction is known as decomposition reaction. Iron sulphate decomposes to form ferric sulphate, sulphur dioxide and sulphur trioxide.
C.The chemical equation of decomposition reaction of $FeS{O_4}$ is
$_{{{ }}Heat} \\\ 2FeS{O_4} \to F{e_2}{O_3} + S{O_2} + S{O_3} \\\$
Decomposition reaction is a reaction in which a compound decomposes into two or more compounds under preferable conditions and factors $AB \to A + B$. Mostly all decomposition reactions require external energy like light, heat or pressure to decompose a compound.

Note:
Ferrous sulphate is used as a supplement of iron and treats iron deficiency. It also helps the body to generate healthy red blood cells which are important for proper functioning of the body as they carry oxygen around the body. But excess ferrous sulphate intake results in constipation and diarrhea.