Acid, any of a class of organic or inorganic water-soluble chemical compounds that taste sour, redden vegetable substances, contain hydrogen, and readily accept electrons or give up protons. Many chemical reactions are speeded up in acid solutions, giving rise to important industrial applications. Strong acids (e.g., hydrochloric acid [HCI]), which break down easily in solution to yield hydrogen (H+) ions, are good electrolytes (conductors of electricity). Amino acids, constitutive of proteins, are essential components of all living systems.
See also: Base.