Bronsted-Lowry Concept Of Acids And Bases-Overview

In 1923, J.N. Bronsted and T.M. Lowry independently proposed definitions of acids and bases based on the concept of proton transfer.

Definitions

Acid: A substance that can donate a proton (H⁺).

Base: A substance that can accept a proton (H⁺).

Example 1: When HCl dissolves in water:

HCl acts as a Bronsted-Lowry acid (donates a proton) and H₂O acts as a Bronsted-Lowry base (accepts the proton).
HCl + H₂O ⇌ H₃O⁺ + Cl⁻

Example 2: When Ammonia (NH₃) dissolves in water:

NH₃ acts as a base and H₂O acts as an acid.
NH₃ + H₂O ⇌ NH₄⁺ + OH⁻

The Bronsted-Lowry concept applies to both aqueous and non-aqueous (e.g., gaseous) reactions.
A substance can only act as an acid if another substance acts as a base, and vice versa.
It is broader than the Arrhenius concept and includes more chemical reactions.
All Arrhenius acids and bases also qualify as Bronsted-Lowry acids and bases.
A Bronsted-Lowry acid must contain a proton to donate.
Some substances can behave as both acids and bases depending on the reacting partner (amphoteric substances).

Certain substances like SO₃ behave as acids even though they cannot donate protons.
Some basic substances like CaO do not accept protons but still show basic behavior.
The concept does not explain acid-base behavior of species like BF₃ (which are explained by Lewis theory).