Editing Nitric acid (section)

===Acid-base properties===
Nitric acid is normally considered to be a [[strong acid]] at ambient temperatures. There is some disagreement over the value of the acid dissociation constant, though the [[acid dissociation constant|p''K''<sub>a</sub>]] value is usually reported as less than −1. This means that the nitric acid in diluted solution is fully dissociated except in extremely acidic solutions. The p''K''<sub>a</sub> value rises to 1 at a temperature of 250&nbsp;°C.<ref name=scdb>[http://www.acadsoft.co.uk/scdbase/scdbase.htm IUPAC SC-Database] A comprehensive database of published data on equilibrium constants of metal complexes and ligands</ref>

Nitric acid can act as a base with respect to an acid such as [[sulfuric acid]]:

{{block indent|{{chem2|HNO3 + 2 H2SO4 ⇌ [NO2]+ + [H3O]+ + 2 HSO4−}};}}
{{block indent|{{pad|3em}}[[Equilibrium constant]]: ''K'' ≈ 22}}

The [[nitronium ion]], {{chem2|[NO2]+}}, is the active reagent in [[aromatic nitration]] reactions. Since nitric acid has both acidic and basic properties, it can undergo an autoprotolysis reaction, similar to the [[self-ionization of water]]:

{{block indent|{{chem2|2 HNO3 ⇌ [NO2]+ + NO3- + H2O}}}}