Question

what is the discrimination window of water​

Answer 1

Leveling effect or solvent leveling refers to the effect of solvent on the properties of acids and bases. The strength of a strong acid is limited ("leveled") by the basicity of the solvent. Similarly the strength of a strong base is leveled by the acidity of the solvent. When a strong acid is dissolved in water, it reacts with it to form hydronium ion (H3O+).[2] 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 perchloric acid (HClO4), aqueous hydrochloric acid (HCl) and aqueous nitric acid (HNO3) are all completely ionized, and are all equally strong acids.[3]

Similarly, when ammonia is the solvent, the strongest acid is ammonium (NH4+), thus HCl and a super acid exert the same acidifying effect.

The same argument applies to bases. In water, OH− is the strongest base. Thus, even though sodium amide (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.[1]