{{Short description|Chemical compound of formula CaS}} {{chembox | Verifiedfields = changed | Watchedfields = changed | verifiedrevid = 460015006 | Name = Calcium sulfide | ImageFile = Calcium-sulfide-3D-balls.png | ImageName = Calcium sulfide | IUPACName = Calcium sulfide | OtherNames = Calcium monosulfide,<br/>Hepar calcies,<br/>Sulfurated lime<br/>Oldhamite |Section1={{Chembox Identifiers | ChemSpiderID_Ref = {{chemspidercite|correct|chemspider}} | ChemSpiderID = 8373113 | UNII_Ref = {{fdacite|correct|FDA}} | UNII = 1MBW07J51Q | InChI = 1/Ca.S/rCaS/c1-2 | ChEBI = 81055 | SMILES = [Ca]=S | InChIKey = JGIATAMCQXIDNZ-WSLZQIQFAE | InChI1 = 1/Ca.S/q+2;-2 | InChIKey1 = AGVJBLHVMNHENQ-UHFFFAOYAE | SMILES1 = [Ca+2].[S-2] | StdInChI_Ref = {{stdinchicite|correct|chemspider}} | StdInChI = 1S/Ca.S/q+2;-2 | StdInChIKey_Ref = {{stdinchicite|correct|chemspider}} | StdInChIKey = AGVJBLHVMNHENQ-UHFFFAOYSA-N | CASNo = 20548-54-3 | CASNo_Ref = {{cascite|correct|CAS}} | PubChem = 10197613 | RTECS = | EINECS = 243-873-5 | KEGG_Ref = {{keggcite|correct|kegg}} | KEGG = C17392 }} |Section2={{Chembox Properties | Formula = CaS | MolarMass = 72.143 g/mol | Appearance = white crystals <br> hygroscopic | Density = 2.59 g/cm<sup>3</sup> | Solubility = Hydrolyses | SolubleOther = Insoluble in alcohol <br> reacts with acid | MeltingPtC = 2525 | MeltingPt_notes = | BoilingPt = | RefractIndex = 2.137 }} |Section3={{Chembox Structure | CrystalStruct = Halite (cubic), cF8 | SpaceGroup = Fm<u style="text-decoration:overline">3</u>m, No. 225 | Coordination = Octahedral (Ca<sup>2+</sup>); octahedral (S<sup>2−</sup>) | LattConst_a = 0.56908 nm<ref>{{cite web |title=ChemicalBook |url=https://www.chemicalbook.com/ChemicalProductProperty_EN_CB3391370.htm}}</ref> }} |Section7={{Chembox Hazards | ExternalSDS = | MainHazards = Reacts with water to release H<sub>2</sub>S | NFPA-H = 2 | NFPA-F = 0 | NFPA-R = 3 <!-- Source from 2014: https://www.sigmaaldrich.com/MSDS/MSDS/DisplayMSDSPage.do?country=US&language=en&productNumber=409553&brand=ALDRICH&PageToGoToURL=https%3A%2F%2Fwww.sigmaaldrich.com%2Fcatalog%2Fsearch%3Fterm%3Dcalcium%2Bsulfide --> | GHSPictograms = {{GHS05}}{{GHS07}}{{GHS09}} | GHSSignalWord = Warning | HPhrases = {{H-phrases|315|319|335|400}} | PPhrases = {{P-phrases|261|273|305+351+338}} }} |Section8={{Chembox Related | OtherAnions = Calcium oxide | OtherCations = Magnesium sulfide<br/>Strontium sulfide<br/>Barium sulfide | OtherFunction_label = sulfides | OtherFunction = Sodium sulfide }} }}
'''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 H<sub>2</sub>S, 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<sup>2−</sup> ion is surrounded by an octahedron of six Ca<sup>2+</sup> ions, and complementarily, each Ca<sup>2+</sup> ion surrounded by six S<sup>2−</sup> ions.
==Production== CaS is produced by carbothermic reduction of calcium sulfate, which entails the conversion of carbon, usually as charcoal, to carbon dioxide: :CaSO<sub>4</sub> + 2 C → CaS + 2 CO<sub>2</sub> and can react further: :3 CaSO<sub>4</sub> + CaS → 4 CaO + 4 SO<sub>2</sub>
In the second reaction the sulfate (+6 oxidation state) oxidizes the sulfide (−2 oxidation state) to sulfur dioxide (+4 oxidation state), while it is being reduced to sulfur dioxide itself (+4 oxidation state).
CaS is also a byproduct in the Leblanc process, a once major industrial process for producing sodium carbonate. In that process sodium sulfide reacts with calcium carbonate:<ref>{{cite encyclopedia|author=Christian Thieme|title=Sodium Carbonates |encyclopedia=Ullmann's Encyclopedia of Industrial Chemistry|publisher=Wiley-VCH|location=Weinheim|year=2000|doi=10.1002/14356007.a24_299|isbn=978-3527306732}}</ref> :Na<sub>2</sub>S + CaCO<sub>3</sub> → CaS + Na<sub>2</sub>CO<sub>3</sub> Millions of tons of this calcium sulfide byproduct was discarded, causing extensive pollution and controversy.<ref name="Kiefer">{{cite journal |last1=Kiefer |first1=David M. |date=January 2002 |url=http://pubs.acs.org/subscribe/journals/tcaw/11/i01/html/01chemchron.html |title=It was all about alkali |journal=Today's Chemist at Work |volume=11 |issue=1 |pages=45–6}}</ref>
Milk of lime, Ca(OH)<sub>2</sub>, 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.<ref>Holleman, A. F.; Wiberg, E. "Inorganic Chemistry" Academic Press: San Diego, 2001. {{ISBN|0-12-352651-5}}.</ref>
==Reactivity and uses== Calcium sulfide decomposes upon contact with water, including moist air, giving a mixture of Ca(SH)<sub>2</sub>, Ca(OH)<sub>2</sub>, and Ca(SH)(OH). :CaS + H<sub>2</sub>O → Ca(SH)(OH) :Ca(SH)(OH) + H<sub>2</sub>O → Ca(OH)<sub>2</sub> + H<sub>2</sub>S
It reacts with acids such as hydrochloric acid to release toxic hydrogen sulfide gas. : CaS + 2 HCl → CaCl<sub>2</sub> + H<sub>2</sub>S
Calcium sulfide is phosphorescent, and will glow a blood red for up to an hour after a light source is removed.<ref>{{Cite web | url=https://www.technoglowproducts.com/red-glow-in-the-dark-powder-calcium-sulfide/ |title = Red Glow in the Dark Powder - Calcium Sulfide}}</ref>
As a noxious byproduct of the Leblanc process, it can be converted to calcium carbonate and hydrogen sulfide, the latter of which can be used as a sulfur source for the lead chamber process to produce the sulfuric acid necessary for the Leblanc process: :{{chem2| CaS(s) + CO2(g) + H2O(l) -> CaCO3(s) + H2S(g)}}
== 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.<ref>{{Cite web|url=https://www.mindat.org/min-2970.html|title=Oldhamite}}</ref><ref>{{Cite web|url=https://www.ima-mineralogy.org/Minlist.htm|title=List of Minerals|date=21 March 2011}}</ref> Burning of coal dumps can also produce the compound.<ref name="Kruszewski">{{cite journal |last1=Kruszewski|first1=Ł. |date=January 2006 |url=https://www.researchgate.net/publication/285329328 |title=Oldhamite-periclase-portlandite-fluorite assemblage and coexisting minerals of burnt dump in Siemianowice Ślaskie-Dabrówka Wielka area (Upper Silesia, Poland) - preliminary report |journal=Mineralogia Polonica - Special Papers |volume=28 |pages=118–120}}</ref>
==See also== * Glossary of meteoritics
==References== {{Reflist}}
{{Calcium compounds}} {{Sulfides}} {{Meteorites}}
Category:Monosulfides Category:Calcium compounds Category:Corrosive substances Category:Meteorite minerals Category:Phosphors and scintillators Category:Rock salt crystal structure