Complex Formation of Aluminium Chloride in Acidified Aqueous Solution

A complex is a molecule or ion formed by a central metal atom or ion (in this case, aluminium) and a group of surrounding molecules or ions (in this case, chloride ions). In acidified aqueous solution, aluminium chloride (AlCl3) forms a complex 'A', in which the hybridisation state of Al is 'B'.

The Complex A

The complex A formed by aluminium chloride in acidified aqueous solution is AlCl4-. This complex ion is formed by the reaction of AlCl3 with HCl in water:

AlCl3 + HCl → AlCl4- + H+

The Hybridisation State of Al

The hybridisation state of Al in the AlCl4- complex ion is sp3. This means that the Al atom is bonded to four atoms or groups of atoms (in this case, four Cl ions) in a tetrahedral arrangement. The four Cl ions are located at the corners of the tetrahedron, with the Al atom at the center.

Explanation

When aluminium chloride is added to an acidified aqueous solution, it undergoes hydrolysis to form Al3+ and Cl- ions. These ions then react with HCl present in the solution to form the complex ion AlCl4-.

The Al atom in the AlCl4- complex ion has a valence electron configuration of 3s23p1, with three valence electrons in the 3p orbital. To form four bonds with the four Cl ions, the Al atom must promote one of its 3s electrons to the 3p orbital, giving it four unpaired electrons in the 3p orbital. These four electrons then undergo sp3 hybridisation to form four sp3 hybrid orbitals, each of which can overlap with a Cl ion to form a covalent bond.

In conclusion, in acidified aqueous solution, aluminium chloride forms the complex ion AlCl4-, in which the hybridisation state of Al is sp3.

A (the complex) is [Al(H2O)6]3+ and,
B (hybridisation state of Al) is 3+