Cobalt(II) chloride
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.
Contents
Properties
Chemical
Physical
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)
Preparation
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.
Availability
Cobalt carbonate can be purchased from pottery stores and 30% Hydrochloric acid can be bought at hardware stores.
Projects
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.
Handling
Safety
Ld50(for rats): 80mg/kg'
Eye and hand protection should be worn while handling this compound.
Storage
Cobalt chloride should be stored in an air tight container to counter its strong hygroscopic nature.
