Question

Which reaction cannot give anhydrous $AlC{l_3}$.
A.Heating of $AlC{l_3}.6{H_2}O$
B.Passing dry $HCl$ overheated aluminium powder.
C.Passing dry $C{l_2}$ overheated aluminium powder.
D.Heating a mixture of alumina and coke in a current of dry $C{l_2}$

Answer 1

Hint: The term anhydrous is used for the substance that does not have water. In the case of crystalline compounds, we get anhydrous compounds when the water of crystallization is removed.

Complete step by step answer:
Anhydrous aluminium chloride is prepared by passing dry hydrochloride gas overheated aluminium metal. The chemical reaction for the preparation of anhydrous aluminium chloride by passing dry hydrochloride gas overheated aluminium powder is given as:
$2Al + 6HCl \to 2AlCl + 3{H_2}$
Hence option B is used for the preparation of anhydrous aluminium chloride.
In case of option C If we pass dry chlorine gas overheated aluminium powder also gives anhydrous aluminium chloride.
Hence option C is also used for the preparation of anhydrous aluminium chloride.
In case of D when a mixture of alumina and coke is heated in a current of dry chlorine gas it also gives anhydrous aluminium chloride. The chemical reaction for it is given as:
$A{l_2}{O_3} + 3C + 3C{l_2} \to 2AlC{l_3} + 3CO$

Hence we can say that option D is also used for the preparation of anhydrous aluminium chloride.
In the case of an option A, on heating $AlC{l_3}.6{H_2}O$ water of crystallization evaporated because $AlC{l_3}$ is covalent. When it reacts with water it forms hydroxide. Hence option A is not used for the preparation of anhydrous aluminium chloride.


So, the correct answer is Option A.

Note:
Anhydrous aluminium chloride is a strong lewis acid. It is used to promote chlorination of aromatic compounds and is also used to promote Friedel- craft reaction acylation.