Cobalt(II) chloride is a colorful compound with the formula CoCl2. Three hydrates of cobalt chloride exist, anydrous, dihydrate, and hexahydrate. All three hydrates are hygroscopic, with the anhydrous a light blue color, and the di and heptahydrate violet. All three are useful reagents which are commonly used as starting points for reactions involving cobalt.




Molecular formula: CoCl2

Melting point: 735 °C (anhydrous), 100 °C (dihydrate), 86 °C (hexahydrate)

Boiling point: 1049 °C

Molar mass: 129.839 g/mol (anhydrous), 165.87 g/mol (dihydrate), 237.93 g/mol (hexahydrate)

Density: 3.356 g/cm  (anhydrous), 2.477 g/cm (dihydrate), 1.924 g/cm (heptahydrate)

Solubility in water: 52.9 g/100 mL (20 °C)


Cobalt(II) chloride in solution.


Cobalt chloride heptahydrate can be synthesized by reacting two moles of hydrochloric acid with one mole of cobalt chloride. Add a small amount of acid and then stir the mixture before adding another small portion, as the CO2 created can cause the mixture to overflow. Usually there will be a layer of unreacted cobalt carbonate/other contaminants which must be filter out using either vacuum or gravity filtration if order to receive a pure product.

CoCO3 + 2 HCl → CoCl2 + CO2+ H2O

By heating this solution to dryness a light blue powder will be formed which is anhydrous cobalt chloride.

If heptahydrate crystals are desired the solution may be dried in a desiccator.



Anhydrous cobalt chloride.

Cobalt carbonate can be purchased from pottery stores and 30% Hydrochloric acid can be bought at hardware stores.


Cobalt chloride is the starting point of many interesting reactions such as Hexamminecobalt (III) chloride and Potassium cobaltinitrite. Combined with a solution of Sodium hypochlorite, it precipitates Cobalt(III) Oxide.



Ld50(for rats): 80mg/kg'

Eye and hand protection should be worn while handling this compound.


Cobalt chloride should be stored in an air tight container to counter its strong hygroscopic nature.



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