Question

Which of the following is Lewis acid?

• A. \(\text{BaCl}_2\)
• B. \(\text{KCl}\)
• C. \(\text{BeCl}_2\)
• D. \(\text{LiCl}\)

Hint:

A Lewis acid accepts an electron pair, so look for the electron deficient molecule.

Answer 1

The Correct Option is C

Step 1: Understanding the Concept:
A Lewis acid is a species that can accept a pair of electrons. Electron deficient molecules with a vacant orbital on the central atom are typical Lewis acids.

Step 2: Key Formula or Approach:
In \(\text{BeCl}_2\), beryllium has only \(4\) electrons in its valence shell after forming two bonds. It has empty orbitals and can accept electron pairs.

Step 3: Detailed Explanation:
\(\text{BeCl}_2\) forms chain polymers in the solid state, using chlorine lone pairs to fill the empty orbitals of Be. It also reacts with \(\text{Cl}^-\) to form \([\text{BeCl}_4]^{2-}\). So it is a Lewis acid.
\(\text{BaCl}_2\), \(\text{KCl}\) and \(\text{LiCl}\) are ionic salts. Their cations are large and have noble gas configurations, and they show no tendency to accept electron pairs, so they are not Lewis acids.

Final Answer:
\(\text{BeCl}_2\) is the Lewis acid, option (C). \[ \boxed{\text{BeCl}_2} \]