Question

Anhydrous $AlC{l_3}$ is covalent but hydrated $AlC{l_3}.6{H_2}O$ is ionic because -
A.$AlC{l_3}$ has planar structure
B.$AlC{l_3}$ dissolves in $C{S_2}$
C.$IE$ of $Al$ is low
D.Hydration energy of all compensates the $IE$

Answer 1

The meaning of anhydrous is that, if a substance is anhydrous it means it contains no water. When we say that a substance is hydrated we mean that the mentioned substance contains water in them.

Complete answer:
$AlC{l_3}$ is covalent while hydrated $AlC{l_3}$ is ionic because we know that ${3^{rd}}$ ionization enthalpy of $Al$ is very high so, therefore it uses a lot of energy for the required in conversion of $Al$ to $A{l^{3 + }}$ .
$Al\left( g \right)$ $+$ 5114{\text{ }}kJ/mol$$$ \to $ A{l^{3 + }}\left( g \right)$ + $ $3{e^ + }$ Therefore, we can say that it prefers to form covalent bonds with $Cl$ atoms . However, it is seen that, whenAlC{l_3}$is dissolved in water, it then undergoes the hydration process releasing a lot of energy$AlC{l_3} + {H_2} \to {\text{ }}AlC{l_3}.6{H_2}O{\text{ }} + {\text{ }}E Where $E$ is energy, and this same energy is enough for removing $3{e^ - }$ from the $Al$ atom . In fact, it is seen that $Al$ does not exist asA{l^{3 + }}$but exist as${\left[ {Al{{\left( {{H_2}O} \right)}_6}} \right]^ + }$${\left[ {Al{{\left( {{H_2}O} \right)}_6}} \right]^ + }{\text{ }} + {\text{ }}C{l^ + } Thus , we can conclude that the hexa - hydrated aluminium chloride is ionic in nature. Now due to high polarisation power of $A{l^{3 + }}$ , the anhydrous $AlC{l_3}$ is covalent in nature . Once it is hydrated it forms as - $AlC{l_3}$ $ + $ $6{H_2}O$ $ \to ${\left[ {Al{{\left( {{H_2}O} \right)}_6}} \right]^ + }$$ $+$ $3C{l^ - }$
Because of the hydration energy power of the $A{l^{3 + }}$ is higher than ionization energy, therefore the $AlC{l_3}.6{H_2}O$ is ionic .

Hence, option D is correct.
Note:
We should keep in mind that the Ionic bonds result from transfer of electrons, while the covalent bonds are formed by sharing of electrons . It is known that Ionic bonds are electrostatic in nature, which results from the attraction of the positive and negative ions and that in turn result from the electron transfer process and also the charge separation between covalently bonded atoms is less extreme.