Definition and Uses: Iron (III) chloride, also called ferric chloride, is an industrial-scale metal. The chemical formula of the compound is FeCl 3. The color of iron (III) chloride crystals depends on the viewing angle, with reflected light the crystals appear dark green, but with transmitted light they appear purple-red. Anhydrous iron (III) chloride is soluble in moist air, forming mists of hydrated hydrogen chloride. Rarely, some fumaroles are observed in their natural state, mainly known as the mineral molysite.
When dissolved in water, iron (III) chloride undergoes hydrolysis and gives off heat in an exothermic reaction. The resulting brown, acidic and corrosive solution is used as a coagulant in wastewater treatment and drinking water production, and as an etchant for copper-based metals in printed circuit boards. Anhydrous iron (III) chloride is a fairly strong Lewis acid and is used as a catalyst in organic synthesis.