Question

The crystals of ferrous sulphate on heating gives:
A. $FeO + S{O_2} + {H_2}O$
B. $F{e_2}{O_3} + {H_2}S{O_4} + {H_2}O$
C. $F{e_2}{O_3} + S{O_2} + S{O_3}$
D. $FeO + S{O_3} + {H_2}S{O_4} + {H_2}O$

Answer 1

The formation of coloured inorganic compounds by heating results due to the decomposition of the transition metal compounds to a new compound. Transition metal involves various colours due electronic transitions between the central metal ion and the bonded molecules.

Complete answer:
The ferrous sulphate crystals are compounds of transition metals. The formation of new products from the decomposition of parent compounds can be observed and determined by the respective colour change.
Colour in transition metal compounds originates from electronic transitions which are of two types:
i. charge transfer transitions: In this case the electron jumps from a ligand orbital to vacant metal orbital hence also known as ligand-to-metal charge-transfer (LMCT) transition. As a result the compounds of the metals appear coloured in visible light.
ii. d-d transitions: In this case the electron jumps from one d-orbital of the metal ion to another d-orbital . The orbitals of transition metal do not have the same energy and as a result the electrons move from lower to higher energy and show colour during the transitions.
The given compound is ferrous sulphate crystals. It is the compound of $F{e^{2 + }}$ cation and $S{O_4}^{2 - }$ anion. The molecule exists in crystal form which contains water of crystallization. Thus the formula of ferrous sulfate crystals is $FeS{O_4}.2{H_2}O$ and it is light green in colour.
On heating the colour changes into white as a water molecule is released and anhydrous ferrous sulphate is formed. The anhydrous ferrous sulfate on further heating gives reddish brown ferric oxide along with sulphur dioxide and sulphur trioxide. The corresponding reaction is
$FeS{O_4}.2{H_2}O\xrightarrow{\Delta }FeS{O_4}(anhydrous)\xrightarrow{\Delta }F{e_2}{O_3} + S{O_2} + S{O_3}$
Hence option C is the correct answer.
The product of the reaction is brown in colour which indicates that the product is $F{e_2}{O_3}$ and not $FeO$ which is black in colour. Further sulfuric acid is not formed as a byproduct in the decomposition reaction and hence the other options are incorrect.
Therefore, the correct option is C.

Note:
A decomposition reaction is a type of reaction by which a compound undergoes breakdown to produce small compounds. This reaction requires external energy in the form of heat.