Cobalt(II) hydroxide

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Cobalt(II) hydroxide
Red cobalt hydroxide.JPG
Red cobalt(II) hydroxide
Blue cobalt hydroxide.JPG
Blue cobalt(II) hydroxide
IUPAC name
Cobalt(II) hydroxide
Other names
Cobaltous hydroxide, cobalt hydroxide, cobaltous hydrate
3D model (Jmol)
ECHA InfoCard 100.040.136
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)[1]
3.20 mg/L
Solubility soluble in acids, ammonia; insoluble in dilute alkalis
79.0 J·mol−1·K−1[2]
-539.7 kJ·mol−1
Safety data sheet Oxford University
Harmful Xn
R-phrases R20 R21 R22 R36 R37 R38 R43
S-phrases S24 S26 S36 S37 S39[3]
NFPA 704
Flammability code 0: Will not burn. E.g., water Health code 1: Exposure would cause irritation but only minor residual injury. E.g., turpentine Reactivity code 2: Undergoes violent chemical change at elevated temperatures and pressures, reacts violently with water, or may form explosive mixtures with water. E.g., phosphorus Special hazards (white): no codeNFPA 704 four-colored diamond
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.[1][4] It has the brucite or cadmium iodide crystal structure.[5]


Cobalt(II) hydroxide is most commonly used 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]


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]

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]

Cobalt hydroxide nanotubes. Scale bars: (a,b) 500 nm, inset 200  nm; (c,e) 50 nm; (d) 100  nm.[8]


  1. ^ a b c d Patnaik, Pradyot (2003). Handbook of Inorganic Chemical Compounds. McGraw-Hill Professional. p. 243. ISBN 0-07-049439-8. Retrieved 2009-03-27. 
  2. ^ Lide, David R. (1998). Handbook of Chemistry and Physics (87 ed.). Boca Raton, FL: CRC Press. p. 513. ISBN 0-8493-0594-2. 
  3. ^ "Safety (MSDS) data for cobalt (II) hydroxide". Oxford University. Retrieved 2009-03-27. 
  4. ^ Lide, David R. (1998). Handbook of Chemistry and Physics (87 ed.). Boca Raton, FL: CRC Press. p. 454. ISBN 0-8493-0594-2. 
  5. ^ a b Wiberg, Nils; Wiberg, Egon; Holleman, A. F. (2001). Inorganic Chemistry. Academic Press. pp. 1478–1479. ISBN 0-12-352651-5. Retrieved 2009-03-27. 
  6. ^ Jayashree, R. S.; Kamath, P. Vishnu (1999). "Electrochemical synthesis of a-cobalt hydroxide". Journal of Materials Chemistry. 9 (4): 961–963. doi:10.1039/A807000H. 
  7. ^ Xu, Z. P.; Zeng, H. C. (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. 
  8. ^ Ni, Bing; Liu, Huiling; Wang, Peng-Peng; He, Jie; Wang, Xun (2015). "General synthesis of inorganic single-walled nanotubes". Nature Communications. 6: 8756. doi:10.1038/ncomms9756. PMC 4640082Freely accessible. PMID 26510862.