What qualifies sulfuric acid as a lewis acid?
Sulfuric acid can supply up to 2 H+ ions per molecule, and H+ ions are Lewis Acids.
A Lewis acid is any substance, such as the H+ ion, that can accept a pair of nonbonding electrons. In other words, a Lewis acid is an electron-pair acceptor.
A Lewis base is any substance, such as the OH- ion, that can donate a pair of nonbonding electrons. A Lewis base is therefore an electron-pair donor.