Acids and Alkalis
Arrhenius, Lowry and Brønsted.
Arrhenius defined an acid as a substance which produces hydrogen ionswritten H+(aq) in water
Lowry and Brønsted defined an acid as a proton donorand a base as a proton acceptor.
If you look at the reaction below
hydrochloric acid + water hydroxonium ion + chloride ionHCl(aq) + H2O(l) H3O+(aq) + Cl-(aq)
According to Arrhenius, hydrochloric acid is an acidbecause it produces hydrogen ions in water(hydrogen ions in water become hydroxonium ions).
According to Lowry and Brønstedhydrochloric acid is an acid because it is a proton donor.A proton is a hydrogen ion.A proton donor is a substance which gives a hydrogen ion away.If you look at the reaction abovehydrochloric acid gives a hydrogen ion to water.
A base is a proton acceptor.This means that a base will gain a hydrogen ion.Water is a base when it is put with hydrochloric acidbecause water will gain a hydrogen ion to become H3O+.
acid + base acid + base

HCl(aq) + H2O(l) H3O+(aq) + Cl-(aq)
On the right side of the arrow, H3O+ is an acidbecause it can give away a hydrogen ion to become H2O.Cl- is a base because it can gain a hydrogen ion to become HCl.
Is water always a base according to Lowry and Brønsted?