Calcium peroxide

Calcium peroxide
Identifiers
CAS Number	1305-79-9 ;
3D model (JSmol)	Interactive image;
ChEBI	CHEBI:48233 ;
ChemSpider	14096 ;
ECHA InfoCard	100.013.764
E number	E930 (glazing agents, ...)
PubChem CID	14779;
RTECS number	EW3865000;
UNII	7FRO2ENO91 ;
CompTox Dashboard (EPA)	DTXSID4050489 ;
	InChI InChI=1S/Ca.O2/c;1-2/q+2;-2 Key: LHJQIRIGXXHNLA-UHFFFAOYSA-N ; InChI=1/Ca.O2/c;1-2/q+2;-2 Key: LHJQIRIGXXHNLA-UHFFFAOYAW;
	SMILES [Ca+2].[O-][O-];
Properties
Chemical formula	CaO2
Molar mass	72.0768 g/mol
Appearance	white or yellowish powder
Odor	odorless
Density	2.91 g/cm3
Melting point	~ 355 °C (671 °F; 628 K) (decomposes)
Solubility in water	decomposes
Acidity (pKa)	12.5
Magnetic susceptibility (χ)	-23.8·10−6 cm3/mol
Refractive index (nD)	1.895
Structure
Crystal structure	Orthorhombic[1]
Space group	Pna21
Coordination geometry	8[1]
Hazards
	Lethal dose or concentration (LD, LC):
LD50 (median dose)	>5000 mg/kg (oral, rat) ; >10000 mg/kg (dermal, rat)
Related compounds
Other anions	Calcium oxide
Other cations	Strontium peroxide; Barium peroxide; Sodium peroxide
	Except where otherwise noted, data are given for materials in their standard state (at 25 °C [77 °F], 100 kPa).
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	Infobox references

Calcium peroxide or calcium dioxide is the inorganic compound with the formula CaO₂. It is the peroxide (O₂²⁻) salt of Ca²⁺. Commercial samples can be yellowish, but the pure compound is white. It is almost insoluble in water.[2]

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 acid, it forms hydrogen peroxide.

Preparation

Calcium peroxide is produced by combining calcium salts and hydrogen peroxide:

Ca(OH)₂ + H₂O₂ → CaO₂ + 2 H₂O

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.[2]

In agriculture it is used in the presowing treatments of rice seed. Also, calcium peroxide has found use in the 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 also used for curing polythioether polymers by oxidising terminal thiol groups to disulphide bridges.

References

Zhao, X.; Nguyen, M.C.; Wang, C.Z.; Ho, K.M. (2013). "Structures and stabilities of alkaline earth metal peroxides XO2 (X = Ca, Be, Mg) studied by a genetic algorithm" (PDF). RSC Advances. doi:10.1039/C3RA43617A.
Harald Jakob, Stefan Leininger, Thomas Lehmann, Sylvia Jacobi, Sven Gutewort. "Peroxo Compounds, Inorganic". Ullmann's Encyclopedia of Industrial Chemistry. Weinheim: Wiley-VCH. doi:10.1002/14356007.a19_177.pub2.CS1 maint: multiple names: authors list (link)

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[a1-1] Zhao, X.; Nguyen, M.C.; Wang, C.Z.; Ho, K.M. (2013). "Structures and stabilities of alkaline earth metal peroxides XO2 (X = Ca, Be, Mg) studied by a genetic algorithm" (PDF). RSC Advances. doi:10.1039/C3RA43617A.

[Ullmann-2] Harald Jakob, Stefan Leininger, Thomas Lehmann, Sylvia Jacobi, Sven Gutewort. "Peroxo Compounds, Inorganic". Ullmann's Encyclopedia of Industrial Chemistry. Weinheim: Wiley-VCH. doi:10.1002/14356007.a19_177.pub2.CS1 maint: multiple names: authors list (link)