(Iron(III) chloride, perchlorure de fer,
ou trichlorure de fer).
2 Fe (solid) + 3 Cl2
(gas) >>> 2 FeCl3
(anhydrous) : FeCl3
Molar mass FeCl3 = 162,2
(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
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) :
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.
Anhydrous iron(III) chloride may be prepared by union of the
Solutions of iron(III) chloride are produced industrially both
from iron and from ore, in a closed-loop process.
- Dissolving pure iron in a solution of iron(III) chloride
Fe(s) + 2 FeCl3(aq) >>> 3 FeCl2(aq)
- Dissolving iron ore in hydrochloric acid
Fe3O4(s) + 8 HCl(aq) >>> FeCl2(aq) + 2 FeCl3(aq) + 4
- Oxidation of iron (II) chloride with chlorine
2 FeCl2(aq) + Cl2(g) >>> 2 FeCl3(aq)
- Oxidation of iron (II) chloride with oxygen
FeCl2(aq) + ¼O2 + HCl >>> FeCl3(aq) +
Like many other hydrated metal chlorides, hydrated iron(III)
chloride can be converted to the anhydrous salt by refluxing with
Conversion of the hydrate to anhydrous iron(III) chloride is not
accomplished by heating, as HCl and iron oxychlorides are
It is available in various solid or liquid forms
(depending on the manufacturer):
- crystalline solid,
- approximately 40% solution of ferric chloride
Main properties :
Solide form (anhydrous)
Volumetric mass density
( 20 °C)
2804 kg/m³ (±7) -
1820 kg/m3 (hexahydrate)
Chloride (Cl), by weight
306 °C (579 K) - 37 °C
Dynamic Viscosity (at 20
12 cP (Pure water : 1.0020
Solubility in water (soft) depending
the temperature :
(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
Ferric chloride react with dissolved calcium
or 30°F as TAC
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.
Standard products used for the production of drinking
French Bulletin - Chlorure ferrique : NF EN 888.
- 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
- 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
- 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
Other uses :
- Used in anhydrous form as a drying reagent in certain
- 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
- 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
- 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.
- 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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