The Arrhenius theory proved to be inadequate. For example, it did not explain why CO₃^2-salts form basic solutions.

In the Bronsted-Lowry [local] theory, the CO₃^2- reacts with solvent water to form HCO₃^- and OH^-. Essentially a Bronsted-Lowry acid is a proton donor and a Bronsted-Lowry base is a proton acceptor. Some metal ions [local] form acidic solutions, and this behavior can be explained by the Bronsted-Lowry theory.