Cobalt(II) carbonate

Cobalt(II) carbonate is a chemical compound with the formula CoCO
3. It is a pink, slightly magnetic powder. It is part of the process used to make cobalt metal from ores. It is also used as a dye and also to make other chemicals called catalysts. Cobalt(II) carbonate also is found as the rare red/pink mineral spherocobaltite.

Cobalt(II) carbonate
[[Image: Co2+ CO 32- |180px]]
IUPAC name	Cobalt(II) carbonate
Other names	Cobaltous carbonate; cobalt(II) salt
Identifiers
CAS number	513-79-1
PubChem	10565
SMILES	C(=O)([O-])[O-].[Co+2]
InChI InChI=1/CH2O3.Co/c2-1(3)4;/h(H2,2,3,4);/q;+2/p-2
Properties
Molecular formula	CoCO3
Molar mass	118.941 g/mol
Appearance	pink solid
Density	4.13 g/cm3
Melting point	427 °C, 700 K, 801 °F
Solubility in water	0.000142 g/100 mL (20 °C)
Solubility product (Ksp)	1.0·10−10
Solubility	soluble in acid negligible in alcohol, methyl acetate insoluble in ethanol
Refractive index (nD)	1.855
Structure
Crystal structure	Rhombohedral (anhydrous) Trigonal (hexahydrate)
Thermochemistry
Std enthalpy of formation ΔfHo298	−722.6 kJ/mol
Standard molar entropy So298	79.9 J/mol·K
Hazards
NFPA 704	0 2 0
Except where noted otherwise, data are given for materials in their standard state (at 25 °C, 100 kPa)

Preparation and structure

Structure of solid cobalt(II) carbonate shown with space-filling ions. Color code: red = O, green = Co, blck = C

Cobalt(II) carbonate is made by mixing liquid cobalt(II) sulfate with sodium bicarbonate:

CoSO
4 + 2 NaHCO
3 → CoCO
3 + Na
2SO
4 + H
2O + CO
2

This reaction is used to remove cobalt from a liquid made from its heated ores.

CoCO₃ has a structure like calcite. The cobalt atoms are arranged in a shape called octahedral.

Reactions

Like most carbonates of transition metals, cobalt carbonate does not dissolve in water, but reacts easily with mineral acids:

CoCO
3 + 2 HCl + H
2O → [Co(H
2O)
6]Cl
2 + CO
2

It is used to make many cobalt coordination complexes. One notable complex made from cobalt(II) carbonate is tris(acetylacetonato)cobalt(III), made by reacting with acetylacetone and hydrogen peroxide.

When cobalt carbonate is heated, it behaves like most carbonates during calcining, but the product becomes partly oxidized.

6 CoCO
3 + O
2 → 2 Co
3O
4 + 6 CO
2

The Co
3O
4 can change back and forth into CoO at high temperatures.

Uses

Cobalt carbonate is used to make other cobalt compounds, including carbonyls and salts. It is added to dietary supplements because the body needs small amounts of cobalt. It is also used to make blue paint for pottery, especially in Delftware.

Related compounds

There are at least two known cobalt(II) carbonate-hydroxides, Co
2(CO
3)(OH)
2 and Co
6(CO
3)
2(OH)
8 · H₂O.

Spherocobaltite is a somewhat rare natural form of cobalt carbonate. Good samples are found in the Republic of Congo. "Cobaltocalcite" is a type of calcite that contains cobalt. It looks very similar to spherocobaltite.

Sodium tris(carbonato)cobalt(III) is a chemical made of cobalt in the +3 oxidation state. It has three carbonate groups attached to the cobalt. This compound is an example of a cobalt(III) coordination complex, where cobalt is connected to other molecules called ligands.

Safety

Scientists have rarely seen how toxic cobalt carbonate is. Animals, including humans, need small amounts of cobalt, which is part of vitamin B12.