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Chromium (III) Oxide

Chromium (iii) oxide, commonly called chromia and referred to as oxo(oxochromiooxy)chromium in IUPAC nomenclature, is an inorganic compound containing chromium and oxygen represented by the chemical formula Cr2O3 [1]. It naturally occurs as the mineral eskolaite and is a highly insoluble compound with high thermal stability, having the properties of both an acid and a base [2, 3, 4].

Chromium (III) Oxide Identification

CAS Number 1308-38-9 [1]
PubChem CID 517277 [1]
ChemSpider ID 451305 [5]
UN Number 3077 [1]
EC Number 215-160-9 [1]
RTECS Number GB6475000 [1]
InChI Key QDOXWKRWXJOMAK-UHFFFAOYSA-N [1]

Chromium (III) Oxide Formula

How is Chromium (III) Oxide Prepared

It is produced through the reduction of sodium dichromate using sulfur at high temperatures indicated by the redox reaction [6]:

Na2Cr2O7 + S → Na2SO4 + Cr2O3

Ammonium dichromate, on heating, decomposes into chromium (iii) oxide, water, and nitrogen [7]:

(NH4)2Cr2O7 → Cr2O3 + N2 + 4H2O

Chromium (iii) carbonate is heated to form chromium (iii) oxide and carbon dioxide:

Cr2(CO3)3 → Cr2O3 + 3CO2

Reaction with Other Compounds

Chromium (III) Oxide with Hydrochloric Acid

It reacts with dilute hydrochloric acid to form chromium (iii) chloride and water [8]:

Cr2O3 + 6HCl → 2CrCl3 + 3H2O

Chromium (III) Oxide with Hydrogen Sulfide

When chromium (iii) oxide reacts with gaseous hydrogen sulfide, it yields chromium (iii) sulfide and water:

Cr2O3 + 3H2S → Cr2S3 + 3H2O

Properties and Characteristics of Chromium (III) Oxide

General Properties

Molar Mass/Molecular Weight 151.989 g/mol [1, 3]

Physical Properties

Color and Appearance Dry, light or dark green, fine crystalline powder [1, 3]
Melting Point 2,435 °C, 4,415 °F [1]
Boiling Point 4,000 °C, 7,230 °F [1]
Density 5.22 g cm-3 [1, 3]
State of matter at room temperature Solid [1, 3]
Solubility Insoluble in acetone and alcohol, very slightly soluble in alkalies and acids [1]
Solubility in Water Practically insoluble, 2.96 µg/L (20 °C, pH 8), 3.13 µg/L (20 °C, pH 6) [1]
Magnetic Susceptibility (χ)  1960.0 X 10-6 cm3/mol

Atomic Properties

Crystal Structure Hexagonal

Chromium (III) Oxide

Uses

  • Because of its stability, chromium (iii) oxide is used as the green pigment in inks, glasses, and paints and as a colorant for ceramics, as well as producing a faint green tinge in glazes [8].
  • It serves as an abrasive for polishing or stropping the edges of razors, knives, and surfaces of optical devices [9].

Is It Safe

Exposure to chromium (iii) oxide through mouth and skin can cause acute toxicity [1]. It may cause an allergic skin reaction and serious eye damage [1]. It can also cause reproductive toxicity and is harmful to the unborn child [1].

References

  1. Chromium(III) Oxide – Pubchem.ncbi.nlm.nih.gov
  2. Chromium Oxide Powder (Cr2O3) – Reade.com
  3. Chromium(III) Oxide – Americanelements.com
  4. Chemistry of Chromium – Chem.libretexts.org
  5. Chromium(III) Oxide – Chemspider.com
  6. Chemical Equations – Chemequations.com
  7. Stoichiometry of Ammonium Dichromate Decomposition – Dartmouth.edu
  8. Chromium Oxide – Chromestarchemicals.com
  9. 5 Interesting Facts About Green Chrome Oxide – Basstechintl.com

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