Johannes Bronsted’ a Danish chemist and Thomas Lowry an English chemist together gave a valuable definiti.on of acids and bases in 1923.
Concept of Acids:
According to Bronsted-Lowry, ‘A substance which has a tendency to donate one or more protons (W) is called an acid, Example: HCI is an acid because it can donate a pair of a proton to a compound which accepts it.
In the aqueous soln of Hcl, the HCI molecule an acid gives a proton to H20 molecule, forming H30 ion.
Hence HCI is a proton donor and therefore an acid.
Concept of Base:
According to Bonsted-Lowry, a base is a species or substance which accepts or tends to accept a proton.
Example: Ammonia NH3 accepts a proton from water H20, to form NH/ Hence ammonia NH3 is a base.