Question

In $FeS{O_4}.7{H_2}O,{H_2}O$ represent:
a.- Molar mass
b.- Molecular weight
c.- Molar weight
d. - Water of crystallisation

Answer 1

Try elimination methods of solving questions. In which try all options then find which is not appropriate for the question. Here ${H_2}O$ can’t be any kind of weight then try to find what kind of water it is.

Complete step by step solution:
Molar mass, molecular weight and molar weight are the numeric values which gives information about the formula weight or the weight of one mol of compound. So they can’t be the terms used for the ${H_2}O$ molecule written in the given formula. Then let's discuss the fourth option i.e. water of crystallization.
Water of crystallization is the water present inside the crystal, also known as water of hydration. During one of the process of purification of solid i.e. in crystallization, after purification some pure form of water traps down inside the crystal called as water of crystallization. Basically, "water of crystallization" refers to water which is present in the crystalline framework of a metal complex or a salt, which is not directly bonded to the metal cation. Water of crystallization can be removed easily by heating the sample but the crystalline properties are often lost.
Let’s come to the question back here in $FeS{O_4}.7{H_2}O$molecule, ${H_2}O$ which are water of crystallization and can be evaporated by heating the crystals.

So the correct option is (D), in $FeS{O_4}.7{H_2}O$, ${H_2}O$ is Water of crystallization.

Note: Whenever the water molecules are written after a complete balanced chemical formula with a dot sign then it is always the water of crystallization. Water molecules written in square brackets are ligands