Question

Anhydrous AICI₃ is covalent, From the data given below, predict whether it would remain covalent or become ionic in aqueous solution.

Ionisation energy for Al = 5137kJ mol^-1

ΔH_hydration for Al³⁺ = - 4665kJ mol^-1

ΔH_hydration for Cl^- = - 381 KJ mol^-1

Answer 1

Total hydration energy of Al³⁺ and 3CI^- ions of AlCl₃ (ΔH_hydration)

= (Hydration energy of Al³⁺ + 3 x hydration energy of Cl^-) 

= [-4665 + 3(-381)] kJ mol^-1 

= - 5808 kJ mol^-1 

This amount of energy is more than that required for the ionisation of Al into Al³⁺ (Ionisation energy of Al to Al³⁺). Due to this reason, AlCl₃ becomes ionic in aqueous solution. In aqueous solution, it exists in ionic form as below: