Ferric chloride

Ferric chloride (Iron(III) chloride, perchlorure de fer, ou trichlorure de fer).
Molecular formula (anhydrous) : FeCl₃
Molar mass FeCl₃ = 162,2 g·mol^-1
(Cl = 66,57 %, Fe= 34,43 %)

Anhydrous iron(III) chloride is deliquescent, forming hydrated hydrogen chloride mists in moist air. It is rarely observed in its natural form, mineral molysite, known mainly from some fumaroles. Odor : slight HCl (hydrochloric acid).
The colour of iron(III) chloride crystals depends on the viewing angle: by reflected light the crystals appear dark green, but by transmitted light they appear purple-red.
Hexahydrated FeCl₃ , 6H₂O (M=270.3 g·mol^-1) : yellow.
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 flocculant in drinking water production and sewage treatment, and as an etchant for copper-based metals in printed circuit boards. Anhydrous iron(III) chloride is a fairly strong Lewis acid, and it is used as a catalyst in organic synthesis.

Preparation.
Anhydrous iron(III) chloride may be prepared by union of the elements:

Solutions of iron(III) chloride are produced industrially both from iron and from ore, in a closed-loop process.

1. Dissolving pure iron in a solution of iron(III) chloride
   Fe(s) + 2 FeCl3(aq) >>> 3 FeCl2(aq)
2. Dissolving iron ore in hydrochloric acid
   Fe3O4(s) + 8 HCl(aq) >>> FeCl2(aq) + 2 FeCl3(aq) + 4 H2O
3. Oxidation of iron (II) chloride with chlorine
   2 FeCl2(aq) + Cl2(g) >>> 2 FeCl3(aq)
4. Oxidation of iron (II) chloride with oxygen
   FeCl2(aq) + ¼O2 + HCl >>> FeCl3(aq) + ½H2O

Like many other hydrated metal chlorides, hydrated iron(III) chloride can be converted to the anhydrous salt by refluxing with thionyl chloride.
Conversion of the hydrate to anhydrous iron(III) chloride is not accomplished by heating, as HCl and iron oxychlorides are produced.

It is available in various solid or liquid forms (depending on the manufacturer):

• crystalline solid,
• approximately 40% solution of ferric chloride concentration.

Main properties :

	Solide form (anhydrous)	Solution
% FeCL3	98	40 (about)
% Fe	33.8	13.9
Volumetric mass density ( 20 °C)	2804 kg/m³ (±7) - 1820 kg/m3 (hexahydrate)	1400 kg/m³
Chloride (Cl), by weight	66.2	26.2 %
pH	-	<1
Melting point	306 °C (579 K) - 37 °C (hexahydrate)	-
Solidification point	-	-50 °C
Dynamic Viscosity (at 20 °C)	-	12 cP (Pure water : 1.0020 cP)

Solubility in water (soft) depending the temperature :

Temperature (°C)	Max. Solubilité(g/L)
0	744
20	920

(g/L = g as FeCl₃ per liter)

Chemical action in the water.
The chemical action of the coagulant causes:

• a decrease in the Total Alkalinity (TAC)
• an increase in free CO2
• the addition of Cl-chloride.

A formulation for water treatment.
Ferric chloride react with dissolved calcium bicarbonate.
.....2 FeCl₃.......+ ........3 Ca[HCO₃]₂ ...........>>>.... 2 Fe[OH]₃ .... + ...6CO₂......+........3CaCl2
(2x162,2)=324,4...........(3x162)=486 or 30°F as TAC . ................(2x106,85)=213,7............(6x44)=264.........(3x2x35,5 de Cl)=213

Per 1 mg/L FeCl₃ added there (30/324,4)= 0.092 °F lower Alkalinity (TAC), and is formed (264/324,4)= 0.814 mg of free CO2, and is also formed (213,7/324,4) = 0.659 mg of ferric hydroxide (as insoluble flocs), and(213/324,4)=0.657 mg of dissolved chloride.

Standardization.
Standard products used for the production of drinking water: Official French Bulletin - Chlorure ferrique : NF EN 888.

Uses.

• as water purification
• used in water and wastewater treatment to precipitate phosphate as iron(III) phosphate, and also suspended solids, colloids, and COD
• used to fight against odor problems and for packaging sludge filter press
• as a leaching agent in chloride hydrometallurgy, for example in the production of Si from FeSi. (Silgrain process)
• Another important application of iron(III) chloride is etching copper in two-step redox reaction to copper(I) chloride and then to copper(II) chloride in the production of printed circuit boards
• as catalyst for the reaction of ethylene with chlorine, forming ethylene dichloride (1,2-dichloroethane), an important commodity chemical, which is mainly used for the industrial production of vinyl chloride, the monomer for making PVC
• In the laboratory iron(III) chloride is commonly employed as a Lewis acid for catalysing reactions such as chlorination of aromatic compounds and Friedel-Crafts reaction of aromatics. It is less powerful than aluminium chloride, but in some cases this mildness leads to higher yields, for example in the alkylation of benzene

Other uses :

• Used in anhydrous form as a drying reagent in certain reactions
• Used to detect the presence of phenol compounds in organic synthesis e.g.: examining purity of synthesised Aspirin
• Used by American coin collectors to identify the dates of Buffalo nickels that are so badly worn that the date is no longer visible
• Used by knife craftsmen and sword smiths to stain blades, as to give a contrasting effect to the metal, and to view metal layering or imperfections
• Used to etch the widmanstatten pattern in iron meteorites
• Necessary for the etching of photogravure plates for printing photographic and fine art images in intaglio and for etching rotogravure cylinders used in the printing industry
• Used in veterinary practice to treat overcropping of an animal's claws, particularly when the overcropping results in bleeding
• Reacts with cyclopentadienylmagnesium bromide in one preparation of ferrocene, a metal-sandwich complex
• Sometimes used in a technique of Raku ware firing, the iron coloring a pottery piece shades of pink, brown, and orange
• Used to test the pitting and crevice corrosion resistance of stainless steels and other alloys
• Used in conjunction with NaI in acetonitrile to mildly reduce organic azides to primary amines
• Used in an animal thrombosis model.

Safety.

• Iron(III) chloride is toxic, highly corrosive and acidic. The anhydrous material is a powerful dehydrating agent.
• Although reports of poisoning in humans are rare, ingestion of ferric chloride can result in serious morbidity and mortality. Inappropriate labeling and storage lead to accidental swallowing or misdiagnosis. Early diagnosis is important, especially in seriously poisoned patients.

Effects on the environment.
Ferric chloride may decrease the pH of stream, thus representing a potential threat to aquatic fauna and flora (stream, river, groundwater).

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