- Iron(III) chloride (FeCl₃), also known as ferric chloride, is a highly corrosive and deliquescent inorganic compound consisting of iron in the +3 oxidation state and chloride ions.
- In its anhydrous form, it appears as dark brown to black crystals that sublimate at high temperatures. When exposed to moisture, FeCl₃ readily hydrolyzes, releasing hydrogen chloride gas and forming yellow to orange aqueous solutions that are acidic and often used in a variety of industrial and laboratory processes. The hexahydrate form (FeCl₃·6H₂O) is orange-brown and more stable in humid conditions.
- FeCl₃ is a highly soluble salt and forms complex ions in aqueous solution, such as [Fe(H₂O)₆]³⁺, which may further hydrolyze to produce acidic, yellow to brownish solutions depending on concentration and pH. Its hydrolysis produces iron(III) hydroxide (Fe(OH)₃) and HCl, which contribute to its corrosiveness. FeCl₃ exhibits paramagnetic behavior, consistent with its d⁵ electron configuration, and plays a central role in coordination chemistry due to its ability to accept ligands through Lewis acid interactions.
- Industrially, iron(III) chloride is widely used as a coagulant and flocculant in water and wastewater treatment, where it facilitates the removal of suspended solids, phosphates, and heavy metals. In the electronics industry, it is a key component of etching solutions for copper-based circuit boards. In chemical synthesis, FeCl₃ functions as a Lewis acid catalyst in Friedel–Crafts alkylation and acylation reactions, as well as in oxidative coupling and chlorination processes. Its role as an oxidizing agent makes it valuable in organic and inorganic reactions alike.
- Ferric chloride is commonly produced by chlorinating iron metal or iron(II) chloride at elevated temperatures:
- 2Fe + 3Cl₂ → 2FeCl₃
- It may also be generated by the reaction of iron(III) oxide with hydrochloric acid. In any form, FeCl₃ must be stored in airtight containers to avoid hydrolysis and corrosion of metal surfaces nearby, as the hydrochloric acid vapor can be quite aggressive.
- Despite its widespread utility, FeCl₃ is hazardous. It is highly corrosive, particularly to skin, eyes, and mucous membranes. Contact can cause severe burns, and inhalation of vapors or dust can damage the respiratory tract. Prolonged exposure to its fumes may also corrode metal structures. It is also toxic to aquatic life, so proper containment and neutralization are essential during disposal or spillage.
