Potassium sulfide is an inorganic compound with the formula K<sub>2</sub>S. The colourless solid is rarely encountered, because it reacts readily with water, a reaction that affords potassium hydrosulfide (KSH) and potassium hydroxide (KOH). Most commonly, the term potassium sulfide refers loosely to this mixture, not the anhydrous solid.
It adopts an antifluorite structure, which means that the small K<sup>+</sup> ions occupy the tetrahedral (F<sup>âÂÂ</sup>) sites in fluorite, and the larger S<sup>2âÂÂ</sup> centers occupy the eight-coordinate sites. Li<sub>2</sub>S, Na<sub>2</sub>S, and Rb<sub>2</sub>S crystallize similarly.
It can be produced by heating K<sub>2</sub>SO<sub>4</sub> with carbon (coke):
In the laboratory, pure K<sub>2</sub>S may be prepared by the reaction of potassium and sulfur in anhydrous ammonia.
Sulfide is highly basic, consequently K<sub>2</sub>S completely and irreversibly hydrolyzes in water according to the following equation:
For many purposes, this reaction is inconsequential since the mixture of SH<sup>âÂÂ</sup> and OH<sup>âÂÂ</sup> behaves as a source of S<sup>2âÂÂ</sup>. Other alkali metal sulfides behave similarly.
Potassium sulfides are formed when black powder is burned and are important intermediates in many pyrotechnic effects, such as senko hanabi and some glitter formulations.