Levelling Effect
The tendency of a solvent to reduce all acids or bases stronger than its own ionised forms to the same effective strength.
Unit
Dimensionless
In depth
In water, any acid stronger than H₃O⁺ is completely converted to H₃O⁺, so HCl and HClO₄ appear equally strong. Distinguishing between them requires a less basic solvent such as glacial acetic acid, in which they remain only partially ionised.
Examples in the real world
Perchloric acid is measurably stronger than hydrochloric acid in acetic acid solvent but indistinguishable in water.