Identifying Lewis Acids and Bases
Problem Identify the Lewis acids and Lewis bases in the following reactions:
(a) H^+ + OH^− \xrightleftharpoons[]{} H_2O (b) Cl^− + BCl_3 \xrightleftharpoons[]{} BCl_4^− (c) K^+ + 6H_2O \xrightleftharpoons[]{} K(H_2O)_6^+
Plan We examine the formulas to see which species accepts the electron pair (Lewis acid) and which donates it (Lewis base) in forming the adduct. The Lewis base must have a lone pair of electrons.
Solution (a) The H^+ ion accepts an electron pair from the OH^− ion in forming a bond. H^+ is the Lewis acid and OH^− is the Lewis base.
(b) The Cl^− ion has four lone pairs and uses one to form a new bond to the central B. BCl_3 is the Lewis acid and Cl^− is the Lewis base.
(c) The K^+ ion does not have any valence electrons to provide, so the bond is formed when electron pairs from O atoms of water enter empty orbitals on K^+.
K^+ is the Lewis acid and H_2O is the Lewis base.
Check The Lewis acids (H^+ , BCl_3, and K^+) each have an unfilled valence shell that can accept an electron pair from the Lewis base (OH^−, Cl^−, or H_2O).