 | |
| Names | |
|---|---|
| IUPAC name Calcium sulfide | |
| Other names Calcium monosulfide, Hepar calcies, Sulfurated lime Oldhamite | |
| Identifiers | |
3D model (JSmol) | |
| ChEBI | |
| ChemSpider |
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| ECHA InfoCard | 100.039.869 |
| EC Number |
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| KEGG |
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| UNII | |
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| Properties | |
| CaS | |
| Molar mass | 72.143 g/mol |
| Appearance | white crystals hygroscopic |
| Density | 2.59 g/cm3 |
| Melting point | 2,525 °C (4,577 °F; 2,798 K) |
| Hydrolyses | |
| Solubility | Insoluble inalcohol reacts withacid |
Refractive index (nD) | 2.137 |
| Structure | |
| Halite (cubic),cF8 | |
| Fm3m, No. 225 | |
a = 569.08 nm[1] | |
| Octahedral (Ca2+); octahedral (S2−) | |
| Hazards | |
| Occupational safety and health (OHS/OSH): | |
Main hazards | Reacts with water to release H2S |
| GHS labelling: | |
   | |
| Warning | |
| H315,H319,H335,H400 | |
| P261,P273,P305+P351+P338 | |
| NFPA 704 (fire diamond) | |
| Related compounds | |
Otheranions | Calcium oxide |
Othercations | Magnesium sulfide Strontium sulfide Barium sulfide |
Relatedsulfides | Sodium sulfide |
Except where otherwise noted, data are given for materials in theirstandard state (at 25 °C [77 °F], 100 kPa). | |
Calcium sulfide is thechemical compound with the formulaCaS. This white material crystallizes in cubes like rock salt. CaS has been studied as a component in a process that would recyclegypsum, a product offlue-gas desulfurization. Like many salts containingsulfide ions, CaS typically has an odour ofH2S, 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 assodium chloride indicating that the bonding in this material is highlyionic. The high melting point is also consistent with its description as an ionic solid. In the crystal, eachS2− ion is surrounded by anoctahedron of six Ca2+ ions, and complementarily, each Ca2+ ion surrounded by six S2− ions.
CaS is produced bycarbothermic reduction ofcalcium sulfate, which entails the conversion of carbon, usually as charcoal, tocarbon dioxide:
and can react further:
In the second reaction thesulfate (+6oxidation state) oxidizes thesulfide (−2 oxidation state) tosulfur dioxide (+4 oxidation state), while it is being reduced to sulfur dioxide itself (+4 oxidation state).
CaS is also a byproduct in theLeblanc process, a once major industrial process for producing sodium carbonate. In that process sodium sulfide reacts withcalcium carbonate:[2]
Millions of tons of this calcium sulfide byproduct was discarded, causing extensive pollution and controversy.[3]
Milk of lime, Ca(OH)2, reacts with elemental sulfur to give a "lime-sulfur", which has been used as aninsecticide. The active ingredient is probably a calciumpolysulfide, not CaS.[4]
Calcium sulfide decomposes upon contact with water, including moist air, giving a mixture of Ca(SH)2, Ca(OH)2, and Ca(SH)(OH).
It reacts withacids such ashydrochloric acid to release toxichydrogen sulfide gas.
Calcium sulfide isphosphorescent, and will glow a blood red for up to an hour after a light source is removed.[5]
As a noxious byproduct of theLeblanc process, it can be converted to calcium carbonate andhydrogen sulfide, the latter of which can be used as a sulfur source for thelead chamber process to produce thesulfuric acid necessary for the Leblanc process:
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.[6][7] Burning of coal dumps can also produce the compound.[8]
