Bases are usually thought of as the chemical opposite of acids. They are commonly defined as compounds that form aqueous solutions that taste bitter, have a high pH (>7), cause litmus paper to turn blue, are slippery to the touch, and react with acids to form water and salts.
In the laboratory, bases are used as reagents or catalysts in many chemical reactions, and some are great conductors of electricity. In an industry setting, bases are used in many applications such as the manufacture of soap, paper, bleaching powder, and the synthetic fiber rayon.
Chemically, bases can be classified as:
- Arrhenius, substances that produce hydroxide (OH−) ions in aqueous solutions, and include sodium hydroxide (lye or caustic soda), potassium hydroxide (or caustic potash), and ammonium hydroxide (or aqua ammonia)
- Brønsted-Lowry, substances such as ammonia (NH3) that can accept a proton or hydrogen ion
- Lewis, compounds such as ammonia, alkyl or aryl amines, and pyridines and pyrimidines that are electron pair donors
NOTE: A Lewis base is also a Brønsted-Lowry base, but a Lewis acid is not necessarily also a Brønsted-Lowry acid.