Many substances can be divided into acids and bases. An acid is a molecule or ion that is able to donate a proton (a H+ ion) or is able to form a covalent bond with an electron pair. A base is a substance that can neutralize an acid by reacting with hydrogen ions. The number of ionizable hydroxide (OH-) ions that exist in one molecule of a basic substance determines the acidity of the base. The base seen in this animation is a monoacidic base which means that it produces one hydroxide ion after complete ionization.