Ampholytes

Ampholytes, or amphoteric electrolytes (from Greek amphoteros - double-sided, dualistic), substances that in aqueous solutions simultaneously exhibit the properties of acids and bases, i.e., are capable of both donating and binding hydrogen and hydroxide ions. They form salt-like compounds with both bases and acids, which is why they received the name amphoteric electrolytes (Bredig) or ampholytes. Certain inorganic ampholytes are known, for example, Al(OH)₃, Pb(OH)₂, which in some cases donate the entire hydroxyl group, while in others only a hydrogen ion. There are particularly many A. among organic substances. They include, in particular, amino acids, peptides, proteins, as well as purine derivatives. Their amphoterism depends on the simultaneous presence of different acidic and basic carboxyl and amino groups attached to the carbon chain. An example is glycine (aminoacetic acid, NH₂.CH₂.COOH), which forms salts with both hydrochloric acid and caustic soda. In the presence of excess acid, A. behave as a base, while in excess alkali they behave as an acid.