Sodium sulfide

Sodium sulfide is a chemical compound with the formula Na2S. More common is its hydrate Na2S·9H2O. Both the anhydrous and the hydrated salts are colorless solids, although technical grades of sodium sulfide are generally yellow to brick red owing to the presence of polysulfides. It is commonly supplied as a crystalline mass, in flake form, or as a fused solid. They are water-soluble, giving strongly alkaline solutions. When exposed to moisture, Na2S is immediately hydrolyzed to give sodium hydrosulfide. Sodium sulfide has an unpleasant rotten egg smell due to the formation of hydrogen sulfide by hydrolysis in moist air. Some commercial samples are described as Na2S·xH2O, where a weight percentage of Na2S is specified. Commonly available grades have around 60% Na2S by weight, which means that x is around 3. These grades of sodium sulfide are often marketed as "sodium sulfide flakes". These samples consist of NaSH, NaOH, and water.