Iron Chlorides

compounds of divalent and trivalent iron with chlorine, FeCl₂ and FeCl₃, respectively; chloride salts. Both salts form crystal hydrates. Ferrous chloride (FeCl₂) is obtained by dissolving iron in hydrochloric acid (particularly during the pickling of steel goods). Bluish green crystals of FeCl₂.6H₂O precipitate out of the solution.

Ferric chloride (FeCl₃) consists of strongly hygroscopic violet crystals with a melting point of 309°C. It forms as a result of heating iron with chlorine or passing chlorine into FeCl₂ solution. Under ordinary conditions it exists as FeCl₃.6H₂O—hygroscopic yellow crystals that are readily soluble in water (91.9 g of anhydrous salt are dissolved in 100 g of water at 20°C). Ferric chloride is used as a mordant in dyeing cloth, a coagulant in water purification, a catalyst in organic synthesis, and so forth.