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 (see States Of Matter). 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 (see Sodium Chloride) 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 bases defines an acid as a compound that
can dissociate in water to yield hydrogen ions (H+) and a base as a compound
that can dissociate in water to yield hydroxyl ions (OH-). The Brönsted-Lowry
theory defines an acid as a Proton donor and a base as a proton acceptor. The Lewis theory defines an acid as a Compound that can accept a pair of electrons and a base as a compound that can donate
a pair of electrons. Each of the three theories has its own advantages and
disadvantages; each is useful under certain conditions. Strong acids, such as Hydrochloric Acid, and strong bases, such as Potassium hydroxide (see Oxidation and Reduction), have a great tendency to dissociate in water and are completely ionized in
solution. Weak acids, such as acetic acid, and weak bases, such as Ammonia, are reluctant to dissociate in water and are only partially ionized in
solution. Strong acids and strong bases make very good Electrolytes (see Electrolysis), i.e., their solutions readily conduct electricity. Weak acids and weak
bases make poor electrolytes.