Sodium sulfide is the chemical compound with the formula Na2S, or more commonly its hydrate Na2S·9H2O. Both are colorless water-soluble salts that give strongly alkaline solutions.
Molar mass： 78.0452 g/mol (anhydrous)
240.18 g/mol (nonahydrate)
Appearance：colorless, hygroscopic solid
Density：1.856 g/cm3 (anhydrous)
1.58 g/cm3 (pentahydrate)
1.43 g/cm3 (nonohydrate)
Melting point：1,176 °C (2,149 °F; 1,449 K) (anhydrous)
100 °C (pentahydrate)
50 °C (nonahydrate)
Solubility in water：12.4 g/100 mL (0 °C)
18.6 g/100 mL (20 °C)
39 g/100 mL (50 °C) (hydrolyses)
Solubility：insoluble in ether
slightly soluble in alcohol
Magnetic susceptibility (χ)：−39.0·10−6 cm3/mol
Crystal structure：Antifluorite (cubic), cF12
Sodium sulfide is primarily used in the kraft process in the pulp and paper industry.
It is used in water treatment as an oxygen scavenger agent and also as a metals precipitant; in chemical photography for toning black and white photographs; in the textile industry as a bleaching agent, for desulfurising and as a dechlorinating agent; and in the leather trade for the sulfitisation of tanning extracts. It is used in chemical manufacturing as a sulfonation and sulfomethylation agent. It is used in the production of rubber chemicals, sulfur dyes and other chemical compounds. It is used in other applications including ore flotation, oil recovery, making dyes, and detergent. It is also used during leather processing, as an unhairing agent in the liming operation.