Article · Wikipedia archive · Last revised May 19, 2026

Cobalt(III) oxide

Cobalt(III) oxide is the inorganic compound with the formula of Co2O3. Although only two oxides of cobalt are well characterized, CoO and Co3O4, procedures claiming to give Co2O3 have been described. The treatment of Co(II) salts such as cobalt(II) sulfate with an aqueous solution of sodium hypochlorite (also known as bleach) gives a black solid:2CoSO4 + 4NaOH + NaOCl → Co2O3 + 2Na2SO4 + NaCl

Last revised
May 19, 2026
Read time
≈ 2 min
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Citations
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Source
Wikipedia ↗
Cobalt(III) oxide1
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Names
IUPAC name
cobalt(III) oxide, dicobalt trioxide
Other names
cobaltic oxide, cobalt sesquioxide
Identifiers
3D model (JSmol)
ChemSpider
ECHA InfoCard 100.013.779
EC Number
  • 215-156-7
RTECS number
  • GG2900000
  • InChI=1S/2Co.3O
    Key: UPWOEMHINGJHOB-UHFFFAOYSA-N
  • O=[Co]O[Co]=O
Properties
Co2O3
Molar mass 165.8646 g/mol
Appearance red powder
Density 5.18 g/cm3 2
Melting point 8953 °C (1,643 °F; 1,168 K)
negligible
+4560.0·10−6 cm3/mol
Structure
Corundum, hR30
R3c, No. 167
Thermochemistry
−577 kJ/mol
Hazards
Occupational safety and health (OHS/OSH):
Main hazards
 toxic
GHS labelling:
GHS07: Exclamation markGHS08: Health hazard
Warning
H302, H317, H351, H410
P280
NFPA 704 (fire diamond)
NFPA 704 four-colored diamondHealth 3: Short exposure could cause serious temporary or residual injury. E.g. chlorine gasFlammability 0: Will not burn. E.g. waterInstability 0: Normally stable, even under fire exposure conditions, and is not reactive with water. E.g. liquid nitrogenSpecial hazard OX: Oxidizer. E.g. potassium perchlorate
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3
0
0
OX
Except where otherwise noted, data are given for materials in their standard state (at 25 °C [77 °F], 100 kPa).
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Cobalt(III) oxide is the inorganic compound with the formula of Co2O3. Although only two oxides of cobalt are well characterized, CoO and Co3O4,4 procedures claiming to give Co2O3 have been described. The treatment of Co(II) salts such as cobalt(II) sulfate with an aqueous solution of sodium hypochlorite (also known as bleach) gives a black solid:56

2CoSO4 + 4NaOH + NaOCl → Co2O3 + 2Na2SO4 + NaCl

Some formulations of the catalyst hopcalite contain "Co2O3".

Some studies have been unable to synthesize the compound, and report that it is theoretically unstable.7

It is soluble in cold diluted sulfuric acid and produces Co2[SO4]3, which is blue in aqueous solution.

Co2O3 + 3H2SO4 → Co2[SO4]3 + 3H2O

Cobalt(III) ion is a strong oxidizer in acidic solution, its standard electrode potential is +1.84V in this situation.8

See also

See also

References

References

  1. Sigma-Aldrich product page
  2. Lide, David R., ed. (2006). CRC Handbook of Chemistry and Physics (87th ed.). Boca Raton, Florida: CRC Press. ISBN 0-8493-0487-3.
  3. "1308-04-9 CAS MSDS (COBALT(III) OXIDE BLACK) Melting Point Boiling Point Density CAS Chemical Properties".
  4. Greenwood, Norman N.; Earnshaw, Alan (1997). Chemistry of the Elements (2nd ed.). Butterworth-Heinemann. doi:10.1016/C2009-0-30414-6. ISBN 978-0-08-037941-8.
  5. Handbook of Preparative Inorganic Chemistry, 2nd Ed. Edited by G. Brauer, Academic Press, 1963, NY. p. 1675.
  6. Hüttner, Erwin (1901-05-02). "Beiträge zur Kenntnis der Oxyde des Kobalts". Zeitschrift für anorganische Chemie (in German). 27 (1). Wiley: 81–124. doi:10.1002/zaac.19010270113. ISSN 0863-1778.
  7. Shanbhag, Pavitra N.; Biswas, Raju K.; Pati, Swapan K.; Sundaresan, Athinarayanan; Rao, Chinthamani Nagesa Ramachandra (2020-11-02). "Elusive Co2O3: A Combined Experimental and Theoretical Study". ACS Omega. 5 (45). American Chemical Society (ACS): 29009–29016. doi:10.1021/acsomega.0c03397. ISSN 2470-1343. PMC 7675568. PMID 33225132.
  8. Guoqing, Wu (2003). 无机化学 (Inorganic Chemistry) (4th ed.). People's Republic of China: 高等教育出版社 (Higher Education Press). p. 781. ISBN 9787040115833.