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.