Dibasic

Dibasic is an adjective used in chemistry to describe substances that have two acidic or basic sites. The term is most often applied to acids that can donate two protons (diprotic or dibasic acids), but it can also describe bases with two basic sites, or salts derived from such acids or bases.

In the context of acids, a dibasic (or diprotic) acid has two ionizable hydrogen atoms. It dissociates in two steps, each releasing one proton, with two corresponding dissociation constants (pKa1 and pKa2). Examples include carbonic acid (H2CO3), sulfurous acid (H2SO3), and oxalic acid (H2C2O4). The first deprotonation typically yields a weak conjugate acid, followed by a second deprotonation to form a doubly negatively charged species in solution.

For bases, a dibasic base has two basic sites capable of accepting protons. This is common in diamines such as ethylenediamine (H2N-CH2-CH2-NH2), where each amine group can be protonated in steps. Monobasic bases, by contrast, have only one available basic site for protonation.

The term also appears in reference to salts, where a dibasic salt contains a dibasic anion or cation. For example, a salt derived from a dibasic acid may contain an anion that can accept two protons, influencing its acidity, solubility, and buffering behavior in solution.

Dibasic consequently contrasts with monobasic and tribasic, reflecting the number of available acidic hydrogens or basic sites. The specific behavior of a dibasic substance depends on the surrounding chemical context, including pH and the presence of other reactive species.