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Through Potassium, Ammonia and Hydrolysis
Structure
It adopts an antifluorite structure, which means that the small K+ ions occupy the tetrahedral (F−) sites in fluorite, and the larger S2− centers occupy the eight-coordinate sites. Li2S, Na2S, and Rb2S crystallize similarly.
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Synthesis and reactions
It can be produced by heating K2SO4 with carbon (coke):
- K2SO4 + 4 C → K2S + 4 CO
In the laboratory, pure K2S may be prepared by the reaction of potassium and sulfur in anhydrous ammonia.
Sulfide is highly basic, so K2S completely and irreversibly hydrolyzes in water according to the following equation:
- K2S + H2O → KOH + KSH
For many purposes, this reaction is inconsequential since the mixture of SH− and OH− behaves as a source of S2−. Other alkali metal sulfides behave similarly.
Potassium polysulfides can be synthesized by reaction of K and S in different ratios:
- 2 K + 3 S → K2S3
Use in fireworks
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.