Chemistry: leveling effect

Tutoring chemistry, concepts are important. The tutor mentions the leveling effect.

The leveling effect is used to explain why, in H₂O, the strongest acid that can exist is H₃O⁺, while the strongest base is OH^–.

If you imagine an acid from the Lewis point of view (see my post about Lewis acids and bases here), an acid can accept an electron pair. A very strong acid will accept one from an H₂O molecule. Then, to maintain its number of lone pairs, same H₂O, now bonded to an extra species via one of its lone pairs, will shed one of its hydrogens as H⁺. That H⁺ will join with a H₂O to become H₃O⁺, now the active acid.

A strong Lewis base will offer its lone pair to one of the hydrogens of a H₂O molecule, effectively removing the H from the H₂O. OH^– is now the effective base.

Source:

chem.libretexts.org

opentextbc.ca