Question

Which of the following is not Lewis acid?

• A. $AlC{l}_3\cdot 6H_{2}O$
• B. $AlC{l}_3$
• C. $BC{l}_3$
• D. All of these

Answer 1

The correct option is A $AlC{l}_3\cdot 6H_{2}O$

Lewis acid : Species which can accept an electron pair using an empty orbital of right energy with the formation of a coordinate bond.

$AlC{l}_3$ acts as a Lewis acid as central atom Al has incomplete octet or empty orbitals. $SnC{l}_4$ and $FeC{l}_3$ act as Lewis acid because $Sn$ and $Fe$ both have vacant d-orbitals.
$AlC{l}_3$ is $s{p}^2$ - hybridised, i.e., it has vacant one 3 p-orbital and five 3d-orbitals. So, central atom has also the ability to accept lone pairs in their empty orbitals.
But in $AlC{l}_3\cdot 6H_{2}O$ one vacant 3p-orbital and five vacant 3d-orbitals are filled by the electron pair oxygen. So $AlC{l}_3\cdot 6H_{2}O$ cannot act as a Lewis acid.