Leveling effect

In chemistry, the leveling effect is the effect of a solvent (especially amphoteric solvents like water) on acids and bases that are dissolved in it.^[2] A solution of an acid can't be stronger than the conjugate acid of the solvent, and a solution of a base can't be stronger than the conjugate base of the solvent.

This chart shows the ranges of acid and base strength for each of the named solvents. The range from 0 to 14 in water is the standard pH scale.^[1]

The conjugate acid of the solvent is called the lyonium ion,^[3] and the conjugate base is called the lyate ion.^[4]

Examples

Acids

Perchloric acid is a much stronger acid than hydrogen chloride in general. Both acids are stronger than the hydronium ion, which is the conjugate acid of water, so in a water solution, they completely react to make hydronium and their conjugate bases:

H₂O + HCl → H₃O⁺ + Cl⁻

H₂O + HClO₄ → H₃O⁺ + ClO−4

Since the actual acid in the solution is hydronium, both solutions will be equally acidic, even though the pure compounds are very different.

Bases

A similar reaction occurs with bases. Sodium amide NaNH₂ and sodium methoxide NaOCH₃ are both one equivalent of different anionic bases, azanide and methoxide. Both of these bases are stronger than the hydroxide ion, which is the conjugate base of water. Just like with acids, these strong bases will react with water, making a solution of the bases' conjugate acids and sodium hydroxide:

H₂O + NaNH₂ → NaOH + NH₃

H₂O + NaOC₂H₅ → NaOH + CH₃OH

Like with acids, these solutions will be equally basic in water despite azanide being much stronger than methoxide in general.