Question

Anhydrous $AlC{{l}_{3}}$ is covalent from the data given below
Lattice energy = 5137 KJ/mol
$\Delta$ H hydration $Al{}^{3+}$ = - 4665 KJ/mol
$\Delta$ H hydration $C{{l}^{-}}$ = - 381 KJ/mol
Identify the correct statement –
A. It will remain covalent in aqueous solution
B. The solution will consists of $Al{}^{3+}$ and $C{{l}^{-}}$
C. The solution will consists of hydrate $Al{}^{3+}$ and $C{{l}^{-}}$
D. None of these

Answer 1

The amount of energy required to convert one mole of an ionic solid into gaseous state is called lattice energy. Lattice energy is also called ionization energy.
The amount of energy released when one moles of an ion undergoes hydration is called hydration energy.

Complete step by step answer:
- In the question they have given the lattice energy of aluminium chloride and hydration energy of aluminium ion and chloride ion.
- We have to check which statement is correct among the given options.
- There is a formula to calculate the total hydration energy of the aluminium chloride and it is as follows.
Total hydration energy of aluminium chloride = (Hydration energy of $A{{l}^{3+}}$ + 3 $\times$ hydration energy of $C{{l}^{-}}$ )
Total hydration energy of aluminium chloride = [-4665+3(-381)] KJ/mol
Total hydration energy of aluminium chloride = -5808 KJ/mol.
- From the above calculation we can say that the hydration energy aluminium chloride is higher than ionization energy of the aluminium chloride.
- Hydration energy (5808 KJ/mol) > Ionization energy (5137 KJ/mol).
- Therefore aluminium chloride is ionic in aqueous solution and it exists in ionic form as follows.
$AlC{{l}_{3}}+6{{H}_{2}}O\to {{(Al{{({{H}_{2}}O)}_{6}})}^{3+}}+3C{{l}^{-}}$

- From the above equation we can say that the solution will consist of hydrate $Al{}^{3+}$ and $C{{l}^{-}}$.
So, the correct answer is “Option C”.

Note: If ionization energy of a molecule is greater than the hydration energy then the molecule is going to exist as a covalent molecule in the aqueous solution. If hydration energy is greater than the ionization energy then the molecule exists in ionic form in the solution.