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]

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

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