These are the two related classes of chemicals, the members of each class have a number of common properties when dissolved in a solvent, usually water. Acids in water solutions exhibit the following common properties they taste sour, turn litmus paper red and react with certain metals, such as zinc, to yield hydrogen gas.

Bases in water solutions exhibit these common properties they taste bitter, turn litmus paper blue and feel slippery.

When a water solution of acid is mixed with a water solution of base, a salt and water are formed this process, called neutralization, is complete only if the resulting solution has neither acidic nor basic properties.

When an acid or base dissolves in water, a certain percentage of the acid or base particles will break up, or dissociate, into oppositely charged ions.

The Arrhenius theory of acids and base defines an acid as a compound that can dissociate water to yield hydrogen ions (H⁺) and a base as a compound that can dissociate in water to yield hydroxyl ions (OH^-).

The Bronsted-Lowry theory defines an acid as a proton donor and a base as a compound that can accept a pair of electrons and a base as a compound that can donate a pair of electrons.