Calcium sulfide
IUPAC name	Calcium sulfide
Other names	Calcium monosulfide, Hepar calcies, Sulfurated lime Oldhamite
Identifiers
CAS number	20548-54-3 Y
PubChem	30182
EC number	243-873-5
Properties
Molecular formula	CaS
Molar mass	72.143 g/mol
Appearance	white crystals hygroscopic
Density	2.59 g/cm3
Melting point	2525 °C
Solubility in water	slightly soluble
Solubility	insoluble in alcohol reacts with acid
Refractive index (nD)	2.137
Structure
Crystal structure	Halite (cubic), cF8
Space group	Fm3m, No. 225
Coordination geometry	Octahedral (Ca2+); octahedral (S2–)
Hazards
EU Index	016-004-00-0
EU classification	Irritant (Xi) Dangerous for the environment (N)
R-phrases	R31, R36/37/38, R50
S-phrases	(S2), S28, S61
Related compounds
Other anions	Calcium oxide
Other cations	Magnesium sulfide Strontium sulfide Barium sulfide
Related sulfides	Sodium sulfide
Except where noted otherwise, data are given for materials in their standard state (at 25 °C, 100 kPa)
Infobox 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 S²⁻ ion is surrounded by an octahedron of six Ca²⁺ ions, and complementarily, each Ca²⁺ ion surrounded by six S²⁻ ions.

Contents 1 Production 2 Reactivity and uses 3 Alternative medicine 4 Natural occurrence 5 References

[edit] Production

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)

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]

[edit] Alternative medicine

Calcium sulfide is used in homeopathy where it is called hepar sulphuris calcareum or hepar sulph.^[2]

[edit] Natural occurrence

Oldhamite is the name for mineralogical form of CaS. It is a rare component of some meteorites and has scientific importance in solar nebula research. Burning of the coal dumps can also produce such compound.

[edit] References

1. ^ Holleman, A. F.; Wiberg, E. "Inorganic Chemistry" Academic Press: San Diego, 2001. ISBN 0-12-352651-5.
2. ^ Hepar Sulphuris. Alternative Medicine Encyclopedia. Encyclopedia of Alternative Medicine. Via Answers.com

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