Cobalt(II) chloride

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Not to be confused with phosgene.
Cobalt(II) chloride
GoodCoClII.jpg
Anhydrous cobalt chloride.
Names
Other names
Cobalt dichloride
Cobaltous chloride
Muriate of cobalt
Properties
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 anhydrous
735 °C (1,355 °F; 1,008 K)
monohydrate
140 °C (284 °F; 413 K)
dihydrate
100 °C (212 °F; 373 K)
hexahydrate
86 °C (187 °F; 359 K)
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 Soluble in ethanol, glycerol, pyridine
Solubility in acetone 8.6 g/100 ml
Solubility in methanol 38.5 g/100 ml
Hazards
Safety data sheet Sigma-Aldrich (anhydrous)
Sigma-Aldrich (hexahydrate)
Flash point Non-flammable
Lethal dose or concentration (LD, LC):
766 mg/kg (rat)
Except where otherwise noted, data are given for materials in their standard state (at 25 °C [77 °F], 100 kPa).
Infobox references

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.

Properties

Chemical

In the presence of ammonia or amines, cobalt(II) is readily oxidized by atmospheric oxygen to give a variety of cobalt(III) complexes, such as hexamminecobalt(III) chloride:

4 CoCl2•6H2O + 4 NH4Cl + 20 NH3 + O2 → 4 [Co(NH3)6]Cl3 + 26 H2O

CoCl2 will react with sodium hypochlorite, to form cobalt(III) oxide.

Physical

Cobalt(II) chloride in solution.

Cobalt(II) chloride is a salt that is blue when anhydrous and pink-purple when hydrated. The compound melts at 735 °C (anhydrous), 100 °C (dihydrate), 86 °C (hexahydrate). It boils at 1049 °C. CoCl2 is soluble in water (52.9 g/100 mL at 20 °C) methanol (38.5 g/100 mL), and slightly soluble in acetone, diethyl ether. The density for the three forms is 3.356 g/cm3 (anhydrous), 2.477 g/cm3 (dihydrate), 1.924 g/cm3 (heptahydrate).

Preparation

Cobalt chloride heptahydrate can be synthesized by reacting two moles of hydrochloric acid with one mole of cobalt carbonate. 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(II) chloride can be purchased from chemical suppliers, both as solid and as solution.

It can also be found in some types of colored silica gel, though the amount is small.

Cobalt(II) chloride, along with other cobalt(II) compounds is classified as "Substance of very high concern" in the EU and its sale is regulated.

Projects

Handling

Safety

Cobalt dichloride is a strong allergen, with a LD50 of 80mg/kg (rats).

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

Storage

Cobalt(II) chloride should be stored in an air tight containers or bags to counter its strong hygroscopic nature.

Disposal

Cobalt dichloride should be neutralized before disposal.

References

Relevant Sciencemadness threads