Sodium sulfide

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Sodium sulfide
General
Name	Sodium sulfide
Other names	Disodium sulfide
Molecular formula	anhydrous: Na₂S, nonahydrate: Na₂S • 9H₂O
Molar mass	anhydrous: 78.046 g/mol, nonahydrate: 240.182 g/mol
Appearance	colorless, hygroscopic solid
CAS number	anhydrous: [1313-82-2] nonahydrate: [1313-84-4]
Properties
Solubility in water	readily soluble
Solubility in alcohol	slightly soluble
pH	alkaline
density	anhydrous: 1.86 g/cm³
melting point	anhydrous: 950 °C

Sodium sulfide is the name used to refer to the chemical compound Na₂S but more commonly its hydrate Na₂S^.9H₂O. Both are a colorless water-soluble salts that give strongly alkaline solutions. When exposed to moist air, Na₂S and its hydrates emit hydrogen sulfide, which smells much like rotten eggs.

1 Structure
2 Production
3 Safety
4 References
5 External links

[edit] Structure

Na₂S adopts the "antifluorite" structure, which means that the Na⁺ centers occupy sites of the fluoride in the CaF₂ framework, and the larger S^2- occupy the sites for Ca²⁺. In solution, the salt, by definition, dissociates. The dianion S^2- does not, however, exist in appreciable amounts in water. Sulfide is too strong of a base to coexist with water. Thus, the dissolution process can be described as follows:

Na₂S + H₂O → Na⁺,SH^- + Na⁺,OH^-

[edit] Production

Industrially Na₂S is produced by reduction of Na₂SO₄ with carbon, in the form of coal:^[1]

Na₂SO₄ + 4 C → Na₂S + 4 CO

In the laboratory, the anhydrous salt can be prepared by reduction of sulfur with sodium in anhydrous ammonia:

2 Na + S → Na₂S

[edit] Safety

Na₂S and its hydrates are dangerous and should only be handled by experts. Like lye, it is strongly alkaline and will cause skin burns. Acids react rapidly to produce H₂S, which is a highly toxic gas. See hydrogen sulfide.