Leveling effect

The term leveling effect refers to a solvent's ability to level the effect of a strong acid or base dissolved in it.

Process

When a strong acid is dissolved in water, it reacts with it to form H₃O⁺ in the following reaction (where "HA" is a generic strong acid such as "HCl"):

HA + H₂O -> A^- + H₃O⁺

Any acid that is stronger than H₃O⁺ reacts with H₂O to form H₃O⁺; therefore, no acid can be stronger than H₃O⁺ in H₂O.

This is true with any solvent, although usually to a lesser extent than with water. Bases may be also leveled in solvents.

Example

Solomons & Fryhle's Organic Chemistry (8th Ed.) describes the leveling effect with the following example:
If you were to add NaNH₂ to water in an attempt to carry out a reaction using the amide ion as the base, the following reaction would take place immediately:

H-O-H + NH₂^- --> H-O^- + NH₃
(Stronger Acid) (Stronger Base) --> (Weaker Base) (Weaker Acid)

The Amide ion would react with water to produce a solution containing hydroxide ions (a much weaker base) and ammonia.

olution

To use bases stronger than the hydroxide ion, use a solvent that is a weaker acid then water.