p-Block Elements-I - Result Question 58

####29. Anhydrous AlCl3 is covalent. From the data given below, predict whether it would remain covalent or become ionic in aqueous solution.

(Ionisation energy for Al=5137kJmol1

ΔHhydration  for Al3+=4665kJmol1 ΔHhydration  for Cl=381kJmol1)

(1997, 2M)

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Solution:

  1. The total hydration energy of AlCl3

= Hydration energy of Al3++3× Hydration energy of Cl

=4665+3(381)kJ/mol

=5808kJ/mol

The above hydration energy is more than the energy required for ionisation of AlCl3 into Al3+ and 3Cl.

Due to this reason, AlCl3 becomes ionic in aqueous solution. In aqueous solution, it is ionised completely as

AlCl3+6H2O[Al(H2O)6]3++3Cl



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