Leveling effect

Leveling effect or solvent leveling refers to the effect of <a href="/facts/Solvent/LoMPMz8S">solvent</a> on the properties of acids and bases. The strength of a <a href="/facts/Strong_acid/vJ4rj6Lu">strong acid</a> is limited ("leveled") by the basicity of the solvent. Similarly the strength of a <a href="/facts/Strong_base/M9wA7qeM">strong base</a> is leveled by the acidity of the solvent. When a strong acid is dissolved in water, it reacts with it to form <a href="/facts/Hydronium/HzE3BGYJ">hydronium</a> <a href="/facts/Ion/3bePpDna">ion</a> (H3O+). An example of this would be the following reaction, where "HA" is the strong acid:

HA + H2O → A− + H3O+
Any acid that is stronger than H3O+ reacts with H2O to form H3O+. Therefore, no acid stronger than H3O+ exists in H2O. For example, aqueous <a href="/facts/Perchloric_acid/gjhK386J">perchloric acid</a> (HClO4), aqueous <a href="/facts/Hydrochloric_acid/HqItJlUT">hydrochloric acid</a> (HCl) and aqueous <a href="/facts/Nitric_acid/UDbwGp6s">nitric acid</a> (HNO3) are all completely ionized, and are all equally strong acids.
Similarly, when <a href="/facts/Ammonia/MtLtJFtz">ammonia</a> is the solvent, the strongest acid is <a href="/facts/Ammonium/jYm8wc1n">ammonium</a> (NH4+), thus HCl and a <a href="/facts/Super_acid/dg82EcNa">super acid</a> exert the same acidifying effect.
The same argument applies to bases. In water, OH− is the strongest base. Thus, even though <a href="/facts/Sodium_amide/VbNjnp43">sodium amide</a> (NaNH2) is an exceptional base (pKa of NH3 ~ 33), in water it is only as good as sodium hydroxide. On the other hand, NaNH2 is a far more basic reagent in ammonia than is NaOH.
The pH range allowed by a particular solvent is called the acid-base discrimination window.

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Leveling effect