Ferric oxide, also called by its IUPAC name iron Trihydrate or iron(III) oxide, is an inorganic compound represented by the chemical formula Fe₂O₃ or Fe₂H₆O₃ ^{[1, 2]}. It is one of the most important oxides of iron, the other two being ferrosoferric oxide (Fe₃O₄) and ferrous oxide (FeO) respectively ^{[3, 4]}. It naturally occurs as the mineral hematite ^[1].

Ferric Oxide Identification
CAS Number	1309-37-1 [2]
PubChem CID	56841934 [2]
ChemSpider ID	452497 [1]
ChEBI	CHEBI:50819 [5]
EC Number	616-935-8 [2]
RTECS Number	NO7400000 [6]
InChI Key	YOBAEOGBNPPUQV-UHFFFAOYSA-N [2]

Hydrated Ferric Oxide

It is a reddish-brown gelatinous compound produced upon addition of alkali to solutions containing Fe(III) salts. It is also called hydrous ferric oxide and can be chemically represented either as Fe₂O₃.H₂O or Fe(O)OH ^[12]. Some common forms of the hydrated ferric oxide include red lepidocrocite that occurs externally in rusticles and orange goethite that occurs on the inside of rusticles.

How is Ferric Oxide prepared

Ferric oxide is synthesized in the laboratory through electrolysis of sodium bicarbonate solution, which acts as an inert electrolyte, and an iron anode. The electrolytic conversion of iron into hydrated iron (III) oxide is represented as:

4Fe + 3O₂ + 2H₂O → 4 FeO(OH)

The hydrated iron (III) oxide, thus produced, undergoes dehydration at around 200 °C to form ferric oxide ^[7].

2 FeO(OH) → Fe₂O₃ + H₂O

Chemical Reactions with Other Compounds

Oxidation of Ferrous Sulfate to Ferric Sulfate

It involves oxidation of ferrous disulfide (FeS₂) to ferrous sulfate (FeSO₄), which is further oxidized to ferric sulfate ^[13]:

1. FeS₂ + 7O+ H₂O → FeSO₄ + H₂SO₄
2. 2FeSO₄ + H₂SO₄ + O → Fe₂(SO₄)₃ + H₂O

Aluminum replaces Iron from Ferric Oxide

Aluminum and ferric oxide undergo a redox reaction by which the metal replaces iron to form aluminum oxide:

Fe₂O₃ + 2Al → Al₂O₃ + 2Fe

Properties and Characteristics of Ferric Oxide

General Properties
Molar Mass/Molecular Weight	159.68820 g/mol [1, 5]
Physical Properties
Color and Appearance	Reddish-brown powder [1, 8]
Melting Point	1538-1566 °C, 2800-2850 °F [8, 9]
Boiling Point	N/A [8]
Density	5.24 g cm-3 [8]
State of matter at room temperature (solid/liquid/gas)	Solid [1]
Solubility	Soluble in warm HCl, slightly soluble in H2SO4 [9]
Solubility in Water	Insoluble [9]
Magnetic Susceptibility (χ)	3.586 X 10-3 emu/Oe.g [10]
Heat Capacity	103.9 J/mol.K
Atomic Properties
Crystal Structure	Rhombohedral (α form), cubic (β and γ forms), orthorhombic (ε form) [11]

Uses

• In iron industries for producing steel and alloys ^[9].
• Ferric oxide powder, also called jeweler’s rouge, is used for polishing lenses and metallic jewelry ^[14].
• Its granular form is used as a filtration media for pulling out phosphates in saltwater aquariums ^[14].
• As FDA-approved Pigment Brown 6 and Pigment Red 101, for use in cosmetics ^[14].
• In biomedical applications, because its nanoparticles are non-toxic and biocompatible ^[14].

Is it Dangerous

Prolonged exposure to its fume or dust can result in pneumoconiosis with fever, chills, aches, shortness of breath, and cough ^[15]. Repeated contact with eyes can discolor it and cause permanent iron staining ^[15].

References
1. Iron(III) oxide – Chemspider.com
2. Ferric Oxide Red – Pubchem.ncbi.nlm.hih.gov
3. Magnetite (Fe₃O₄) – Pubchem.ncbi.nlm.nih.gov
4. Ferrous oxide – Pubchem.ncbi.nlm.nih.gov
5. CHEBI:50819 – ferric oxide – Ebi.ac.uk
6. Iron Oxide Dust and Fume (as Fe) – Cdc.gov
7. Kinetics and mechanism of the dehydration of γ-FeOOH – Researchgate.net
8. Iron(III) Oxide Particles – Americanelements.com
9. Ferric Oxide – Chemicalbook.com
10. Magnetic Properties of Materials – Sigmaaldrich.com
11. Iron(III) Oxide – Chem.libretexts.org
12. Iron Oxide (Fe₂O₃), Hydrate (Compound) – Pubchem.ncbi.nlm.nih.gov
13. The oxidation of ferrous sulfate to ferric sulfate by means of air – Archive.org
14. Uses of Iron Oxide – Zjunited.com
15. Hazardous Substance Fact Sheet Iron Oxide – Nj.gov