Calcium iodide

Calcium iodide
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Template:Longitem	CaI2
Molar mass	293.887 g/mol (anhydrous) ; 365.95 g/mol (tetrahydrate)
Appearance	white solid
Density	3.956 g/cm3 (anhydrous)
Melting point	Template:Chembox CalcTemperatures
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Solubility	soluble in acetone and alcohols
Template:Longitem	−109.0·10−6 cm3/mol
Template:Longitem	Rhombohedral, hP3
Template:Longitem	P-3m1, No. 164
Template:Longitem	octahedral
NFPA 704 (fire diamond)	Template:NFPA 704 diamond
Template:Longitem	calcium fluoride; calcium chloride; calcium bromide
Template:Longitem	beryllium iodide; magnesium iodide; strontium iodide; barium iodide

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Calcium iodide (chemical formula CaI₂) is the ionic compound of calcium and iodine. This colourless deliquescent solid is a salt that is highly soluble in water. Its properties are similar to those for related salts, such as calcium chloride. It is used in photography.^[1] It is also used in cat food as a source of iodine.

Reactions

Henri Moissan first isolated pure calcium in 1898 by reducing calcium iodide with pure sodium metal:^[3]

CaI₂ + 2 Na → 2 NaI + Ca

Calcium iodide can be formed by treating calcium carbonate, calcium oxide, or calcium hydroxide with hydroiodic acid:^[4]

CaCO₃ + 2 HI → CaI₂ + H₂O + CO₂

Calcium iodide slowly reacts with oxygen and carbon dioxide in the air, liberating iodine, which is responsible for the faint yellow color of impure samples.^[5]

2 CaI₂ + 2 CO₂ + O₂ → 2 CaCO₃ + 2 I₂