Hydrosulfides

Hydrosulfides are chemical compounds containing the hydrosulfide anion, HS-. This anion is a conjugate base of hydrogen sulfide (H2S) and can be thought of as a sulfur atom bonded to a hydrogen atom with an overall negative charge. Hydrosulfides are often found as salts where the negative charge of the hydrosulfide anion is balanced by a positive cation, such as sodium hydrosulfide (NaHS) or potassium hydrosulfide (KHS). These salts are typically soluble in water, forming alkaline solutions due to the hydrolysis of the hydrosulfide anion.

In aqueous solutions, hydrogen sulfide and hydrosulfide ions exist in equilibrium, with the ratio depending on the pH. At lower pH values, the equilibrium favors hydrogen sulfide, while at higher pH values, the hydrosulfide ion becomes more prevalent. The hydrosulfide ion is also a weak acid, capable of donating a proton to form the sulfide ion (S2-).

Hydrosulfides are encountered in various natural and industrial settings. They are present in some mineral waters and are produced by the bacterial decomposition of organic matter containing sulfur. Industrially, hydrosulfides are used in several applications. For instance, they are employed in the mining industry for the flotation of certain ores. They can also be used in wastewater treatment to precipitate heavy metals as insoluble metal sulfides. The characteristic odor of rotten eggs is often associated with compounds containing sulfur, including hydrogen sulfide and to some extent, hydrosulfides, though their odor perception can vary.