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Acids And Bases
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.