The tendency of a solvent to make all
Brønsted acids whose
acidity exceeds a certain value appear equally acidic. It is due to the complete transfer
to a
protophilic solvent of a
hydron from a dissolved acid stronger than the
conjugate acid of the solvent. The only acid present to any significant extent in all such solutions
is the
lyonium ion. For example, the solvent water has a levelling effect on the acidities of
HClO4 ,
HCl
and
HI
:
aqueous solutions of these acids at the same (moderately low) concentrations have
the same acidities. A corresponding levelling effect applies to strong bases
protogenic solvents.
Source:
PAC, 1994, 66, 1077
(Glossary of terms used in physical organic chemistry (IUPAC Recommendations 1994))
on page 1135