Arrhenius Theory
The theory defining an acid as a substance that produces H⁺ ions in water and a base as one that produces OH⁻ ions.
Formula / equation
HA → H⁺ + A⁻; BOH → B⁺ + OH⁻
Unit
Dimensionless
In depth
Arrhenius gave the first quantitative account of acids and bases and explained the constant enthalpy of neutralisation. Its limitation is that it applies only to aqueous solutions and cannot explain why ammonia, which contains no hydroxide, is basic.
Examples in the real world
HCl and HNO₃ as Arrhenius acids; NaOH and KOH as Arrhenius bases.