Calcium sulfide

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Calcium sulfide

General
Systematic name	Calcium sulfide
Other names	calcium monosulfide, hepar calcies, sulfurated lime oldhamite
Molecular formula	CaS
Molar mass	72.14 g/mol
Appearance	White solid
CAS number	[20548-54-3]
Properties
Density and phase	2600 kg m^-3, solid
Solubility in water	hydrolysis
Melting point	2400 °C (2673 K)
Boiling point
Structure
Coordination geometry	Octahedral
Crystal structure	Sodium chloride
Hazards
MSDS	External MSDS
Main hazards	H₂S source
NFPA 704	0 1 0
R/S statement	R: 31-36/37/38-50 S: 28-61
RTECS number	N/A
Supplementary data page
Structure and properties	N/A
Thermodynamic data	N/A
Spectral data	N/A
Related compounds
Other anions	CaO
Other cations	MgS, BaS
Related salts	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.

1 Production and uses
2 Reactivity and uses
3 References
4 External links

[edit] 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

[edit] 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]