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Cobalt(II) chloride
Cobaltous chloride anhydrous.jpg
Cobaltous chloride.jpg
IUPAC name Cobalt(II) chloride
Other names Cobaltous chloride
Cobalt dichloride
CAS number 7646-79-9,
16544-92-6 (dihydrate)
7791-13-1 (hexahydrate)
PubChem 3032536
EC number 231-589-4
RTECS number GF9800000
Molecular formula CoCl2
Molar mass 129.839 g/mol (anhydrous)
165.87 g/mol (dihydrate)
237.93 g/mol (hexahydrate)
Appearance blue crystals (anhydrous)
violet-blue (dihydrate)
rose red crystals (hexahydrate)
Density 3.356 g/cm3 (anhydrous)
2.477 g/cm3 (dihydrate)
1.924 g/cm3 (hexahydrate)
Melting point

735 °C (anhydrous)
140 °C (monohydrate)
100 °C (dihydrate)
86 °C (hexahydrate)

Boiling point

1049 °C

Solubility in water 43.6 g/100 mL (0 °C)
45 g/100 mL (7 °C)
52.9 g/100 mL (20 °C)
105 g/100 mL (96 °C)
Solubility 38.5 g/100 mL (methanol)
8.6 g/100 mL (acetone)
soluble in ethanol, ether, pyridine, glycerol
Crystal structure CdCl2 structure
hexagonal (anhydrous)
monoclinic (dihydrate)
Octahedral (hexahydrate)
EU classification Toxic (T)
Carc. Cat. 2
Dangerous for
the environment (N)
EU Index 027-004-00-5
NFPA 704

NFPA 704.svg

R-phrases R49, R60, R22, R42/43, R68, R50/53
S-phrases S53, S45, S60, S61
Flash point Non-flammable
Related compounds
Other anions Cobalt(II) fluoride
Cobalt(II) bromide
Cobalt(II) iodide
Other cations Rhodium(III) chloride
Iridium(III) chloride
Except where noted otherwise, data are given for materials in their standard state (at 25 °C, 100 kPa)

Cobalt(II) chloride, also known as cobaltous chloride and cobalt dichloride, is a chemical compound. It contains cobalt in its +2 oxidation state. Its chemical formula is CoCl2. It contains cobalt and chloride ions.


Cobalt(II) chloride is normally found in the red (or pink) form. The red form has water in it. It can be heated to turn it into the blue form, without water. The blue form will absorb water from the air and turn red again.

A different blue form is made when cobalt(II) chloride is reacted with a chemical compound that has chloride in it. Hydrochloric acid works the best, but sodium chloride can be used too. When it is heated, it turns more blue than when it is cooled. Cobalt chloride can be used to test for chloride ions in this way.

It can be oxidized to cobalt(III) compounds, although cobalt(III) chloride does not exist. If it is made, it just drops a Cl from CoCl3, making CoCl2 (cobalt(II) chloride) again.


The anhydrous (without water) blue form can be made by reacting cobalt with chlorine. The hydrated (with water) red form can be made by reacting cobalt(II) oxide or cobalt(II) hydroxide with hydrochloric acid.


It is used to place cobalt into other chemical compounds. It can be used to make other cobalt compounds. It is the most common cobalt compound in the lab.


It is a weak oxidizing agent, too weak to ignite things. Cobalt compounds are toxic in large quantities, like any other transition metal compounds. They are not toxic like lead or mercury compounds, though.

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