bisulfidu

Bisulfido, also called bisulfide in some contexts, denotes the hydrosulfide anion HS−, the conjugate base of hydrogen sulfide (H2S) in aqueous solution. The term is used in several languages, including Italian and Spanish, where bisulfido or bisulfide sometimes designates the HS− ion.

Chemically, HS− is a weak base and a good nucleophile. It exists in equilibrium with H2S in water: H2S ⇌ HS− + H+. The pKa1 is about 7.0 at 25 °C, so near neutral pH both H2S and HS− are present in appreciable amounts. HS− readily forms salts with alkali metals, such as NaHS and KHS, and it can bind to metal ions to form metal hydrosulfide complexes or precipitates like iron sulfide (FeS).

Occurrence and production: in nature, hydrosulfide arises in anoxic waters and sediments where sulfate-reducing bacteria generate H2S, which can deprotonate to HS−. Industrially, HS− is produced by neutralizing hydrogen sulfide with bases in chemical synthesis, water treatment, and related processes. It also appears as an intermediate in reactions that generate or consume sulfide species under varying pH.

Applications and relevance: HS− serves as a sulfide source in chemical synthesis and as a precipitating agent for metal ions in aqueous systems. In geology and environmental chemistry, hydrosulfide and its salts influence sulfide mineral formation and metal mobility. In biological contexts, hydrogen sulfide is a signaling molecule; the hydrosulfide form participates in redox chemistry and metal binding within various systems.

Safety: hydrogen sulfide is highly toxic; HS− salts can be irritants and may release H2S upon acidification. Adequate ventilation, protective equipment, and careful handling are required when working with sulfide species.