Question

The alkaline earth metal nitrate that does not crystallise with water molecules, is:
(A) $Sr{\left( {N{O_3}} \right)_2}$
(B) $Mg{\left( {N{O_3}} \right)_2}$
(C) $Ba{\left( {N{O_3}} \right)_2}$
(D) $Ca{\left( {N{O_3}} \right)_2}$

Answer 1

Alkaline Earth metals are electro-positive and possess two electrons in their outermost shell making them highly reactive. Alkaline Earth metals are $Be,Mg,Ca,Sr,Ba,Ra$ . Polar ions of nitrate anion attract the polar molecules of water and as the size of the cation is very large very fewer molecules will crystallize. So, the alkaline earth metal nitrate with the largest size of cation doesn’t crystalline with water molecules.

Complete answer:
From the nitrates of alkaline earth metals, Barium Nitrate does not crystalline with molecules of water. Because, Smaller in size of cation more water molecules will crystallize. Due to its largest size of $Ba$ ( Positive ion), $Ba{\left( {N{O_3}} \right)_2}$ ​ doesn't crystallize with water molecules.
Beryllium is the only alkaline earth metal that does not react with water or steam, even when the metal is heated to red heat. In addition, beryllium forms an outer oxide layer to protect the metal and lowers the reactivity of the metal.
Hence, the correct answer is option C. barium nitrate $Ba{\left( {N{O_3}} \right)_2}$ .

Additional Information:
Alkaline earth metal nitrates are prepared in solution and can be crystallized as hydrated salt by the action of $HN{O_3}$ on oxides, hydroxides and carbonates. All nitrates are soluble in water and decompose on heating to give the corresponding oxides with evolution of $N{O_2}$ and ${O_2}$ .

Note:
Note that the salt is highly soluble in water due to less lattice enthalpy. The water of crystallisation is referred to as the number of water molecules present in one formula unit of salt. The water molecules are held together by the special bonding called hydrogen bonding. The hydrogen bonding is a type of weak force that results in the formation of dipole-dipole interaction between a hydrogen atom.