The Brønsted-Lowry Theory of Acids and Bases
A Brønsted-Lowry acid is a proton (hydrogen ion) donor.
A Brønsted-Lowry base is a proton (hydrogen ion) acceptor.
In this theory an acid is a substance that can release a proton (like in the Arrhenius theory) and a base is a substance that can accept a proton. A basic salt such as Na+F- generates OH- ions in water by taking protons from water itself (to make HF):
F−(aq)+H2O(l)⇌HF(aq)+OH−
When a Brønsted acid dissociates, it increases the concentration of hydrogen ions in the solution, [H+]; conversely, Brønsted bases dissociate by taking a proton from the solvent (water) to generate [OH−]