Cobalt(II) hydroxide

Cobalt(II) hydroxide

200px Red cobalt(II) hydroxide
200px Blue cobalt(II) hydroxide
Names
IUPAC name Cobalt(II) hydroxide
Other names Cobaltous hydroxide, cobalt hydroxide, cobaltous hydrate
Identifiers
CAS Number	21041-93-0 Y
ChemSpider	8305419 Y
Jmol 3D model	Interactive image
PubChem	10129900
InChI InChI=1S/Co.2H2O/h;2*1H2/q+2;;/p-2 Y Key: ASKVAEGIVYSGNY-UHFFFAOYSA-L Y InChI=1/Co.2H2O/h;2*1H2/q+2;;/p-2 Key: ASKVAEGIVYSGNY-NUQVWONBAS
SMILES [Co+2].[OH-].[OH-]
Properties
Chemical formula	Co(OH)2
Molar mass	92.948 g/mol
Appearance	rose-red powder or bluish-green powder
Density	3.597 g/cm3
Melting point	168 °C (334 °F; 441 K) (decomposes)
Solubility in water	3.20 mg/L
Solubility product (Ksp)	1.0×10−15
Solubility	soluble in acids, ammonia; insoluble in dilute alkalis
Structure
Coordination geometry	rhombohedral
Thermochemistry
Std molar entropy (So298)	79.0 J·mol−1·K−1
Std enthalpy of formation (ΔfHo298)	-539.7 kJ·mol−1
Vapor pressure	{{{value}}}
Related compounds
Other anions	Cobalt(II) chloride Cobalt(II) bromide Cobalt(II) iodide
Other cations	Iron(II) hydroxide Nickel(II) hydroxide Copper(II) hydroxide
Except where otherwise noted, data are given for materials in their standard state (at 25 °C [77 °F], 100 kPa).
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Infobox references

Cobalt(II) hydroxide or cobaltous hydroxide is the chemical compound composed of cobalt and the hydroxide ion with the formula Co(OH)₂. It occurs in two forms, either as a rose-red powder, which is the more stable of the two forms, or as bluish-green powder. It has the brucite or cadmium iodide crystal structure.

Uses

It finds use as a drying agent for paints, varnishes and inks, in the preparation of other cobalt compounds, as a catalyst and in the manufacture of battery electrodes.

Reactions

Cobalt(II) hydroxide is precipitated when an alkaline hydroxide is added to an aqueous solution of Co²⁺ ions:

CoCl₂ (aq) + 2 NaOH → Co(OH)₂ (s) + 2 NaCl

Cobalt(II) hydroxide decomposes to cobalt(II) oxide at 168 °C under vacuum and is oxidized by air to form cobalt(III) hydroxide, Co(OH)₃. The thermal decomposition product in air above 300 °C is Co₃O₄.

Like iron(II) hydroxide, cobalt(II) hydroxide is primarily a basic hydroxide, although it does form the weakly acidic reddish hexaaquacobalt(II) ion, [Co(H₂O)₆]²⁺, in acidic aqueous solutions. In strong bases, cobalt(II) hydroxide accepts additional hydroxide ions to form dark blue cobaltates(II) [Co(OH)₄]²⁻ and [Co(OH)₆]⁴⁻.

File:Cobalt hydroxide nanotubes.jpg

Cobalt hydroxide nanotubes. Scale bars: (a,b) 500 nm, inset 200  nm; (c,e) 50 nm; (d) 100  nm.