IUPAC name: Iron thichloride
Other names: Ferric chloride, Ferric perchloride
CAS number: 7705-08-0
Ferric chloride is an aqueous solution having a red-brown colour and a characteristic smell.
Ferric chloride is made by the exothermic reaction between ferric oxide and hydrochloric acid: Fe2O3 + 6 HCl → 3 H2O + 2 FeCl3
Ferric chloride is one of the main reagents utilised in water treatment, both in the production of drinking water and in the purification of wastewater. These processes take advantage of the formation of insoluble salts, for example ferric phosphate to remove phosphorous (mainly in the treatment of municipal wastewater), and of the direct formation of ferric hydroxide. Ferric hydroxide, being virtually insoluble at a pH above 6.5, precipitates in the form of bulky flocks that incorporate the finely dispersed particles (silt, for example) and allow their physical separation through simple settling and filtration processes. Ferric chloride facilitates the precipitation of heavy metals and organic compounds; moreover, it reacts with the sulphides present in the sewage, efficiently suppressing unpleasant odours. It is utilised in organic chemistry in the polymerisation of thiophene, both as a catalyst and as an oxidant.