In 1923, Bronsted and Lowry without the essential involvement of a solvent defined acid as a substance which gives up a proton (proton donor) and a base as a substance which accepts a proton (proton acceptor). Thus according to Bronsted-Lowry theory, neutralisation is a process in which protons are transferred from an acid to a base.
1. A substance acts as an acid only when another substance capable of accepting a proton (base) is present.
2. In aqueous solution, H+ ion exists as H3O+ and not as free H+.
3. Not only molecules but even ions may also act as acids and bases.
4. Water, the most common solvent, can act both as an acid as well as a base because it can donate a proton as well as can accept it.
Limitations of Bronsted-Lowry Theory:
Bronsted-Lowry Theory’s excessive emphasis on the presence of proton in all acids exclude substances like SO2, AlCl3, N2O4, SOCl2, NOCl, COCl2, etc. from the category of acids although these are definitely involved in acid-base phenomenon.