Cobalt(II) hydroxide

Cobalt(II) hydroxide
IUPAC name Cobalt(II) hydroxide
Other names Cobaltous hydroxide, cobalt hydroxide, cobaltous hydrate
Identifiers
CAS number	21041-93-0 Y
PubChem	10129900
ChemSpider	8305419 Y
Jmol-3D images	Image 1
SMILES [Co+2].[OH-].[OH-]
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
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	3.20 mg/L
Solubility product, Ksp	1.0×10−15
Solubility	soluble in acids, ammonia; insoluble in dilute alkalis
Structure
Coordination geometry	rhombohedral
Thermochemistry
Std 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]
NFPA 704	0 1 2
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 hydroxide (verify) (what is: Y/N?) 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]

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^[1].

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.^[1] The thermal decomposition product in air above 300 °C is Co₃O₄.^[6][7][8]

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-[5].

References

1. ^ ^{a b c d} Patnaik, Pradyot (2003). Handbook of Inorganic Chemical Compounds. McGraw-Hill Professional. p. 243. ISBN 0070494398. http://books.google.com/?id=Xqj-TTzkvTEC&pg=PA243. Retrieved 2009-03-27. 
2. ^ Lide, David R. (1998). Handbook of Chemistry and Physics (87 ed.). Boca Raton, FL: CRC Press. p. 513. ISBN 0849305942. 
3. ^ "Safety (MSDS) data for cobalt (II) hydroxide". Oxford University. http://msds.chem.ox.ac.uk/CO/cobalt_II_hydroxide.html. Retrieved 2009-03-27. 
4. ^ Lide, David R. (1998). Handbook of Chemistry and Physics (87 ed.). Boca Raton, FL: CRC Press. p. 454. ISBN 0849305942. 
5. ^ ^{a b} Wiberg, Nils; Wiberg, Egon; Holleman, A. F. (2001). Inorganic Chemistry. Academic Press. pp. 1478–1479. ISBN 0123526515. http://books.google.com/?id=LxhQPdMRfVIC&pg=PA1478. Retrieved 2009-03-27. 
6. ^ R. S. Jayashree and P. Vishnu Kamath (1999). "Electrochemical synthesis of a-cobalt hydroxide". Journal of Materials Chemistry 9: 961–963. doi:10.1039/A807000H. 
7. ^ Synthesis of Co3O4 during thermolysis of cobalt hydroxide and binary hydroxides, L.A. Paikina, S.M. Rakhovskaya, L.A. Vereshchagina, Neorganicheskie Materialy. Vol. 19, no. 9, pp. 1508–11. 1983
8. ^ Z. P. Xu and H. C. Zeng (1998). "Thermal evolution of cobalt hydroxides: a comparative study of their various structural phases". Journal of Materials Chemistry 8 (11): 2499–2506. doi:10.1039/A804767G.