How does nitric acid act as a base?

Answer 1

Acids or bases change character based on the solution in which they exist. For instance, HCl is a strong acid in water, but is a weak acid when dissolved in glacial acetic acid. This has to do with the proton affinity of the respective acids and bases. So, nitric acid may act as a base when placed in a solvent that has a lower proton affinity, i.e., the nitric acid will accept the proton as a Bronsted-Lowry base.

I'm not as familiar with Lewis acids and bases, but Lewis bases donate electron pairs, and Lewis acids accept them. I'm sure there is a circumstance in which nitric acid will donate an electron pair to a Lewis acid.

Answer 2

Nitric acid is actually an acid, not a base. When dissolved in water, it donates a proton (H+) to water molecules, forming the nitrate ion (NO3-) and hydronium ion (H3O+) in solution. This reaction makes nitric acid an acidic substance.