Cobalt(II) hydroxide
IUPAC name	Cobalt(II) hydroxide
Other names	Cobaltous hydroxide, cobalt hydroxide, cobaltous hydrate
Identifiers
CAS number	21041-93-0 Y
PubChem	3014696
Properties
Molecular 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 (decomp)[1]
Solubility in water	3.2 g/100mL
Solubility product, Ksp	1.0 x 10-15
Solubility	soluble in acids, ammonia; insoluble in dilute alkalis
Structure
Coordination geometry	rhombohedral
Thermochemistry
Std enthalpy of formation ΔfHo298	-539.7 kJ•mol-1
Standard molar entropy So298	79.0 J•mol-1•K-1[2]
Hazards
MSDS	Oxford University
EU classification	Harmful (H)
R-phrases	R20 R21 R22 R36 R37 R38 R43
S-phrases	S24 S26 S36 S37 S39[3]
Related compounds
Other anions	Cobalt(II) chloride Cobalt(II) bromide Cobalt(II) iodide
Other cations	Iron(II) hydroxide Nickel(II) hydroxide Copper(II) hydroxide
Y (what is this?)  (verify) Except where noted otherwise, data are given for materials in their standard state (at 25 °C, 100 kPa)
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^[1][4]. It has the brucite or cadmium iodide crystal structure^[5].

[edit] Uses

It finds use as a drying agent for paints, varnishes, and inks, in the preparation of other cobalt compounds, as a catalyst, or in the manufacture of battery electrodes^[1].

[edit] Reactions

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

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

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^[1], cobalt(III) oxide hydrate, Co₂O₃·xH₂O, and cobalt(IV) oxide hydrate, CoO₂·xH₂O.

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 colbaltates(II) [Co(OH)₄]^2- and [Co(OH)₆]^4-[5].

[edit] References

v • d • e   Cobalt compounds CoBr2 · Co(CN)2 · CoCO3 · CoCl2 · Co(ClO3)2 · CoF2 · CoF3 · CoI2 · Co(NO3)2 · CoO · Co(OH)2 · CoS · CoSO4 · Co2O3 · Co3O4