Acid   Generally, a substance that reacts with bases to form a salt, several different definitions of acids have been proposed by different scientists (listed in parentheses). 1) (Arrhenius) a compound that releases hydrogen ions (H+) in solution; 2) (Brønsted-Lowry) a compound capable of donating hydrogen ions, 3) (Lewis) a compound that can accept a pair of electrons from a base.

Used in the following modules: Acids and Bases, DNA I, DNA II, Fats and Proteins, Matter, Minerals II, Research Methods: Modeling, Scientific Communication: Peer Review, The Carbon Cycle, The Nitrogen Cycle