Acids , Bases And Salts - Theories

A limitation of the Bronsted Lowery theory is that the extent to which a dissolved substance can act as an acid or a base depends largly on the solvent.

A)HClO₄  +  HF   \( \rightleftharpoons \)     H₂F⁺  +  ClO₄^–  ( HClO₄  acts as a acid in HF ) 
   Acid        Base             Acid       Base

B)HNO₃ behaves as base in HClO₄ and HF 
   HNO₃  +  4HF   \( \rightleftharpoons \)  H₃O⁺  +  NO₂⁺ + 2HF₂^– 
   (base)      (acid)

C)Urea is weak acidic in liquid NH3 
   NH₂CONH₂   +   NH₃   \( \to \)   NH₄⁺   +    NH₂CONH^–
  Acid                     Base         Acid             Base

Note: H₂SO₄ also acts as base in HF solvent.