calcium sulfide

Calcium sulfide
IUPAC name	Calcium sulfide
Other names	calcium monosulfide, hepar calcies, sulfurated lime oldhamite
Identifiers
CAS number	20548-54-3
Properties
Molecular formula	CaS
Molar mass	72.14 g/mol
Appearance	White solid
Density	2600 kg m-3, solid
Melting point	2400 °C (2673 K)
Solubility in water	hydrolysis
Structure
Crystal structure	Sodium chloride
Coordination geometry	Octahedral
Hazards
Main hazards	H2S source
NFPA 704	0 1 0
R-phrases	31-36/37/38-50
S-phrases	28-61
Related Compounds
Other anions	CaO
Other cations	MgS, BaS
Related sulfides	Na2S
Except where noted otherwise, data are given for materials in their standard state (at 25 °C, 100 kPa) Infobox disclaimer and references

Calcium sulfide is the chemical compound with the formula CaS. This white material crystallizes in cubes like rock salt. CaS has been studied as a component in a process that would recycle gypsum, a product of flue gas desulfurization. Like many salts containing sulfide ions, CaS typically has an odour of H₂S, which results from small amount of this gas formed by hydrolysis of the salt.

In terms of its atomic structure, CaS crystallizes in the same motif as sodium chloride indicating that the bonding in this material is highly ionic. The high melting point is also consistent with its description as an ionic solid. In the crystal, each S^2- ion is surrounded by an octahedron of six Ca²⁺ ions, and complementarily, each Ca²⁺ ion surrounded by six S^2- ions.

Production and uses

CaS is produced by "carbothermic reduction" of calcium sulfate, which entails the conversion of carbon, usually as charcoal, to carbon dioxide:

CaSO₄ + 2 C → CaS + 2 CO₂

and can react further:

3 CaSO₄ + CaS → 4 CaO + 4 SO₂

Reactivity and uses

Calcium sulfide decomposes upon contact with water, including moist air, giving a mixture of Ca(SH)₂, Ca(OH)₂, and Ca(SH)(OH).

CaS + H₂O → Ca(SH)(OH) + H₂S

Ca(SH)(OH) + H₂O → Ca(OH)₂ + H₂S

Milk of lime, Ca(OH)₂, reacts with elemental sulfur to give a "lime-sulfur", which has been used as an insecticide. The active ingredient is probably a calcium polysulfide, not CaS.^[1]

References

1. ^ Holleman, A. F.; Wiberg, E. "Inorganic Chemistry" Academic Press: San Diego, 2001. ISBN 0-12-352651-5.

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