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.
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):
Main properties :
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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.
Other uses :
Safety.
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).