ironchloride

Iron chloride refers to two related inorganic compounds of iron and chlorine: iron(II) chloride (FeCl2) and iron(III) chloride (FeCl3). Collectively they are called iron chlorides and are used for their Lewis-acid behavior, redox properties, and chemical reactivity. The anhydrous salts are solids; FeCl2 is a white to pale green crystalline solid that is readily deliquescent in air, while FeCl3 is a dark brown to black hygroscopic solid that forms hydrates such as FeCl3·6H2O.

In water, these compounds behave differently. FeCl2 forms Fe2+ in solution and is easily oxidized to FeCl3 by air. FeCl3 hydrolyzes in water to give acidic solutions and species such as Fe(OH)3, releasing HCl according to the reaction FeCl3 + 3 H2O → Fe(OH)3 + 3 HCl. In concentrated chloride media, ferric chloride can form chloro complexes such as FeCl4−.

Production methods vary. FeCl3 is commonly prepared by direct chlorination of iron metal: 2 Fe + 3 Cl2 → 2 FeCl3. FeCl2 can be made by reacting iron with hydrochloric acid: Fe + 2 HCl → FeCl2 + H2, and it can be further oxidized to FeCl3 in the presence of chlorine or oxygen.

Uses are diverse. FeCl3 is widely used as a coagulant in water and wastewater treatment, as an etchant for copper in printed circuit boards, and as a Lewis acid catalyst in organic synthesis. FeCl2 serves as a reducing agent in organic reactions, in textile dyeing, and in electroplating and other metallurgical processes.

Safety considerations include its corrosivity and potential for skin and eye irritation. Both compounds should be handled with appropriate PPE and stored away from oxidizers.