Cobalt(II) carbonate
Chemical compound
From Wikipedia, the free encyclopedia
Cobalt(II) carbonate is the inorganic compound with the formula CoCO3. This pink paramagnetic solid is an intermediate in the hydrometallurgical purification of cobalt from its ores. It is an inorganic pigment, and a precursor to catalysts.[5] Cobalt(II) carbonate also occurs as the rare red/pink mineral spherocobaltite.[6]
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Co2+ CO32− | |
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| Names | |
|---|---|
| IUPAC name
Cobalt(II) carbonate | |
| Other names
Cobaltous carbonate; cobalt(II) salt | |
| Identifiers | |
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3D model (JSmol) |
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| ChemSpider | |
| ECHA InfoCard | 100.007.428 |
PubChem CID |
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| UNII |
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CompTox Dashboard (EPA) |
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| Properties | |
| CoCO3 | |
| Molar mass | 118.941 g/mol |
| Appearance | pink solid |
| Density | 4.13 g/cm3 |
| Melting point | 427 °C (801 °F; 700 K) [1] decomposes before melting to cobalt(II) oxide (anhydrous) 140 °C (284 °F; 413 K) decomposes (hexahydrate) |
| 0.000142 g/100 mL (20 °C)[2] | |
Solubility product (Ksp) |
1.0·10−10[3] |
| Solubility | soluble in acid negligible in alcohol, methyl acetate insoluble in ethanol |
Refractive index (nD) |
1.855 |
| Structure | |
| Rhombohedral (anhydrous) Trigonal (hexahydrate) | |
| Thermochemistry | |
Std molar entropy (S⦵298) |
79.9 J/mol·K[1] |
Std enthalpy of formation (ΔfH⦵298) |
−722.6 kJ/mol[1] |
Gibbs free energy (ΔfG⦵) |
−651 kJ/mol[1] |
| Hazards | |
| GHS labelling: | |
  [4] | |
| Warning | |
| H302, H315, H317, H319, H335, H351[4] | |
| P261, P280, P305+P351+P338[4] | |
| NFPA 704 (fire diamond) | |
| Lethal dose or concentration (LD, LC): | |
LD50 (median dose) |
640 mg/kg (oral, rats) |
Except where otherwise noted, data are given for materials in their standard state (at 25 °C [77 °F], 100 kPa).
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Preparation and structure
Structure of solid cobalt(II) carbonate shown with space-filling ions. Color code: red = O, green = Co, blck = C
It is prepared by combining solutions of cobalt(II) sulfate and sodium bicarbonate:
- CoSO4 + 2 NaHCO3 → CoCO3 + Na2SO4 + H2O + CO2
This reaction is used in the precipitation of cobalt from an extract of its roasted ores.[5]
CoCO3 adopts a structure like calcite, consisting of cobalt in an octahedral coordination geometry.[7]
Reactions
Aqueous solutions of cobalt chloride can be prepared from cobalt(II) carbonate with hydrochloric acid according to this idealized equation:[8]
- CoCO3 + 2 HCl + 3 H2O → CoCl2·(H2O)4 + CO2
The reaction of cobalt(II) carbonate and acetylacetone in the presence of hydrogen peroxide gives tris(acetylacetonato)cobalt(III).[9]
Heating the carbonate in air (calcining) is accompanied by partial oxidation:
- 6 CoCO3 + O2 → 2 Co3O4 + 6 CO2
The resulting Co3O4 converts reversibly to CoO at high temperatures.[10]
Uses
Cobalt carbonate is a precursor to cobalt carbonyl and various cobalt salts. It is a component of dietary supplements since cobalt is an essential element. It is a precursor to blue pottery glazes, famously in the case of Delftware.
Related compounds
At least two cobalt(II) carbonate-hydroxides are known: Co2(CO3)(OH)2 and Co6(CO3)2(OH)8·H2O.[11]
The moderately rare spherocobaltite is a natural form of cobalt carbonate, with good specimens coming especially from the Republic of Congo. "Cobaltocalcite" is a cobaltiferous calcite variety that is quite similar in habit to spherocobaltite.[6]
Sodium tris(carbonato)cobalt(III) is a cobalt(III) complex containing three carbonate ligands.
Safety
Toxicity has rarely been observed. Animals, including humans, require trace amounts of cobalt, a component of vitamin B12.[5]
