Question

Name a salt that does not contain water of crystallization.

Answer 1

Hint: Water of crystallization is the amount of water molecules present in the crystal structure of a compound such that it is present in a stoichiometric amount and can be easily removed on heating the compound.

Complete step by step solution:
“The fixed number of water molecules which enter into a loose chemical combination with the substance when the substance is crystallized from its hot saturated solution is called water of crystallization”
In simpler terms “Water of crystallization or water of hydration are water molecules that are present inside crystals”. This water is present in a stoichiometric ratio in the compound. This water of crystallization may be directly bonded to the ion in a coordinate complex or it may be present elsewhere in the crystal structure bound by hydrogen bonds. When saturated aqueous solutions of compounds are crystallized, they incorporate water molecules in their crystalline frameworks. This is also responsible for the colour as well as the geometric shape of a crystal. These water molecules can be easily removed from the compound by heating it but the crystalline properties are often lost.
A salt containing water of crystallization is also known as a hydrate. They generally have polymeric structure because of the presence of hydrogen bonds. Some of the examples are:
$CuS{ O }_{ 4 }.5{ H }_{ 2 }O$ - copper(II) sulfate pentahydrate
$Co{ Cl }_{ 2 }.6{ H }_{ 2 }O$ - cobalt(II) chloride hexahydrate
When many of these salts are dissolved in water, the water molecules present as water of crystallization become labilized. “Hydrates are common for salts that contain +2 and +3 cations as well as −2 anions”.
To understand the concept of water of crystallization more clearly, let’s look at an example of nickel(II) chloride hexahydrate which has the formula $Ni{ Cl }_{ 2 }({ H }_{ 2 }O{ ) }_{ 6 }$. This solid consists of $[trans-Ni{ Cl }_{ 2 }({ H }_{ 2 }O{ ) }_{ 4 }]$ subunits in which four water molecules are present in the coordination structure. These sub-units are hydrogen bonded to each other along with two additional molecules of water.
Water is not the only solvent that is found in crystals. In fact, most solvents remain, to a greater or lesser extent, in the crystal. A common example is benzene.
There are many salts that are devoid of water of crystallisation. Some of these salts are: Potassium chloride- ${KCI}$
Sodium Nitrate-$NaN{ O }_{ 3 }$

Note: Baking soda is sodium bicarbonate in anhydrous form and it does not contain any water of crystallization. It is widely used as a dry fire extinguisher because of its alkaline nature.