Hydrated calcium chloride when fused loses water of crystallization to form anhydrous calcium chloride but anhydrous magnesium chloride cannot be prepared by heating magnesium chloride hexahydrate . Why so ?

Explanation

Anhydrous `MgCl_(2)` cannot be prepared by simply heating `MgCl_(2) . 6 H_(2)O` because it gets hydrolysed by its own water of crystallization .
`MgCl_(2) + 6H_(2)O to Mg O + 2 HCl + 5 H_(2)O`
However , if hydrated magnesium chloride is heated in an atmosphere of HCl gas at 650 K , it checks the above hydrolysis reaction and the hydrated magnesium chloride now loses water of crystallization to form anhydrous magnesium chloride now loses water of crystallization to form anhydrous magnesium chloride
`MgCl_(2) . 6 H_(2)O overset(HCl "gas")underset(650K)(to) MgCl_(2) + 6 H_(2)O`.