View source for Calcium peroxide

{{Short description|Chemical compound}}
{{Redirect|CaO2|"CaO2" as a symbol for arterial oxygen content|Hypoxia (medical)#arterial oxygen content}}
{{Chembox
| Watchedfields = changed
| verifiedrevid = 476998612
| Name = Calcium peroxide
| ImageFile = Crystal structure of CaO2.jpg
| ImageName = Calcium peroxide
| OtherNames = {{Unbulleted list
  | Calcium dioxide<ref>{{cite web | url=https://sor.epa.gov/sor_internet/registry/substreg/searchandretrieve/advancedsearch/externalSearch.do?p_type=SRSITN&p_value=82271 | archive-url=https://web.archive.org/web/20230811141657/https://sor.epa.gov/sor_internet/registry/substreg/searchandretrieve/advancedsearch/externalSearch.do?p_type=SRSITN&p_value=82271 | url-status=dead | archive-date=August 11, 2023 | title=Substance Registry Services &#124; US EPA }}</ref>
  }}
|Section1={{Chembox Identifiers
| ChemSpiderID_Ref = {{chemspidercite|correct|chemspider}}
| ChemSpiderID = 14096
| UNII_Ref = {{fdacite|correct|FDA}}
| UNII = 7FRO2ENO91
| InChI = 1/Ca.O2/c;1-2/q+2;-2
| ChEBI_Ref = {{ebicite|correct|EBI}}
| ChEBI = 48233
| EC_number = 215-139-4
| Gmelin = 674257
| KEGG = C18566
| UNNumber = 1457
| SMILES = [Ca+2].[O-][O-]
| InChIKey = LHJQIRIGXXHNLA-UHFFFAOYAW
| StdInChI_Ref = {{stdinchicite|correct|chemspider}}
| StdInChI = 1S/Ca.O2/c;1-2/q+2;-2
| StdInChIKey_Ref = {{stdinchicite|correct|chemspider}}
| StdInChIKey = LHJQIRIGXXHNLA-UHFFFAOYSA-N
| CASNo = 1305-79-9
| CASNo_Ref = {{cascite|correct|CAS}}
| PubChem = 14779
| RTECS = EW3865000
 }}
|Section2={{Chembox Properties
| Ca=1 | O=2
| Density = 2.91 g/cm<sup>3</sup>
| Appearance = white or yellowish powder
| Odor = odorless
| Solubility = decomposes
| MeltingPt= ~
| MeltingPtC = 355
| MeltingPt_notes = (decomposes)
| BoilingPt = 
| pKa = 12.5
| RefractIndex = 1.895
| MagSus = −23.8·10<sup>−6</sup> cm<sup>3</sup>/mol
 }}
|Section3={{Chembox Structure
| CrystalStruct = Orthorhombic<ref name=a1>{{cite journal |journal=RSC Advances |year=2013 |title=Structures and stabilities of alkaline earth metal peroxides XO2 (X = Ca, Be, Mg) studied by a genetic algorithm |first1=X. |last1=Zhao |doi=10.1039/C3RA43617A |last2=Nguyen |first2=M.C. |last3=Wang |first3=C.Z. |last4=Ho |first4=K.M. |volume=3 |issue=44 |page=22135 |bibcode=2013RSCAd...322135Z |url=https://zenodo.org/record/1230026 }}</ref>
| SpaceGroup = Pna2<sub>1</sub>
| Coordination = 8<ref name=a1/>
 }}
|Section7={{Chembox Hazards
| ExternalSDS =
| GHSPictograms = {{GHS03}}{{GHS07}}
| GHSSignalWord = Warning
| HPhrases = {{H-phrases|272|315|319|335}}
| PPhrases = {{P-phrases|210|220|221|261|264|271|280|302+352|304+340|305+351+338|312|321|332+313|337+313|362|370+378|403+233|405|501}}
| LD50 = >5000 mg/kg (oral, rat) <br> >10000 mg/kg (dermal, rat)
 }}
|Section8={{Chembox Related
| OtherAnions = [[Calcium oxide]]
| OtherCations = [[Strontium peroxide]]<br/>[[Barium peroxide]]<br/>[[Sodium peroxide]]
 }}
}}
'''Calcium peroxide''' or '''calcium dioxide''' is the [[inorganic compound]] with the formula CaO<sub>2</sub>. It is the [[peroxide]] (O<sub>2</sub><sup>2&minus;</sup>) salt of Ca<sup>2+</sup>. Commercial samples can be yellowish, but the pure compound is white. It is almost insoluble in [[water]].<ref name = Ullmann>{{Ullmann | title = Peroxo Compounds, Inorganic | vauthors = Jakob H, Leininger S, Lehmann T, Jacobi S, Gutewort S |display-authors=3| doi = 10.1002/14356007.a19_177.pub2}}</ref>

==Structure and stability==
As a solid, it is relatively stable against decomposition. In contact with water however it hydrolyzes with release of oxygen. Upon treatment with an [[acid]], it forms [[hydrogen peroxide]].

<chem>2CaO2 + 2H2O -> 2Ca(OH)2 + O2</chem>

<chem>CaO2 + 2H+ -> Ca^2+ + H2O2</chem>

==Preparation==
Calcium peroxide is produced by combining [[calcium]] salts and [[hydrogen peroxide]]:
:Ca(OH)<sub>2</sub>  +  H<sub>2</sub>O<sub>2</sub>   →   CaO<sub>2</sub>  +  2 H<sub>2</sub>O
The octahydrate precipitates upon the reaction of [[calcium hydroxide]] with dilute [[hydrogen peroxide]]. Upon heating it dehydrates.

==Applications==
It is mainly used as an oxidant to enhance the extraction of precious metals from their ores. In its second main application, it is used as a [[food additive]] under the [[E number]] E930 it is used as [[flour bleaching agent]] and [[improving agent]].<ref name = Ullmann/>

In agriculture it is used in the presowing treatments of [[rice]] seed. Also, calcium peroxide has found use in [[aquaculture]] to oxygenate and disinfect water. In the ecological restoration industry it is used in the treatment of soils. Calcium peroxide is used in a similar manner to [[magnesium peroxide]] for environmental restoration programs. It is used to restore soil and groundwater contaminated with petroleum by the process of enhanced in-situ [[bioremediation]]. It is a minor component of some dentifrices. 

It is also used for curing {{chem name|polythioether}} polymers by oxidising terminal thiol groups to disulphide bridges.{{cn|date=July 2022}}

==References==
{{reflist}}

{{E number infobox 920-929}}
{{Calcium compounds}}
{{Peroxides}}

{{DEFAULTSORT:Calcium Peroxide}}
[[Category:Peroxides]]
[[Category:Calcium compounds]]
[[Category:Food additives]]
[[Category:Bleaches]]
[[Category:Disinfectants]]
[[Category:Oxidizing agents]]