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EC number: 232-140-5
CAS number: 7789-00-6
The substance forms reversible equilibria and the proportion of the species present depends on various environmental factors. An overview of the expected behaviour of the substance in sterile aqueous media is provided in the EU RAR, furthermore the speciation of the substance is affected by various other reducing or oxidising species present:
are no proprietary studies investigating the hydrolysis of the substance
in aqueous media. The substance of interest is an inorganic element and
sufficient information on the speciation of the substance under various
environmental conditions is available in the EU RAR for chromium (VI)
compounds (2005): further details are provided below.
equilibria for chromium (VI)
(VI) is a strong oxidising agent and as a result only exists as
oxygenated species in the environment. For the dichromates, the actual
species present in solution depends on the pH according to the following
+ HCrO4- pKa1
= -0.6; 0.74; 0.86
+ CrO42- pKa2
= 5.9; 6.49; 6.51
these equilibria alone, at very low pH (e.g. near 0) the dominant
species in solution would be the fully protonated form (H2CrO4).
At pHs between 0 around 6-6.5, the dominant chromate species in solution
would be HCrO4-, and at pHs above around 6-6.5 the
main chromate species in solution would be CrO42-.
addition to the above equilibria, the chromate ion is in equilibrium
with the dichromate ion according to the following equilibria:
addition, there are the following base-hydrolysis equilibria:
the available information indicates that at very low pH values (1) the
main species in solution is H2CrO4, at higher pHs
between around 2 and 6, HCrO4- and Cr2O72-will
both be present in equilibrium, and at higher pHs (>7) the main species
present will be CrO42-. Thus at environmental pHs
the species found in solution will be a mixture of Cr2O72-,
HCrO4- and CrO42-,
irrespective of the form in which the chromium (VI) enters solution.
equilibria for chromium (III)
predominant forms of chromium (III) present in solution are Cr3+
at very low pH, then with increasing pH, Cr(OH)2+, Cr(OH)2+,
Cr(OH)3 and finally Cr(OH)4- at very high pH. The
species Cr(OH)2+ is thought to occur only over a
very narrow pH range (approximately pH 6.27-6.84).
solution, the equilibrium between chromium (III) ions and chromium
hydroxide lays well over to the side of the relatively insoluble
hydroxide at pH>5 according to the following equilibrium:
(s) + 3H+ Keq
means that at pHs >5 chromium (III) can be expected to precipitate out
of solution as the insoluble hydroxide, often in conjunction with iron.
However, complexation of chromium (III) ions with organic matter (such
as citric acid, diethylenetriaminepentaacetic acid (DTPA), fulvic acid)
can result in increased solubilisation of chromium (III) at higher pHs.
Information on Registered Substances comes from registration dossiers which have been assigned a registration number. The assignment of a registration number does however not guarantee that the information in the dossier is correct or that the dossier is compliant with Regulation (EC) No 1907/2006 (the REACH Regulation). This information has not been reviewed or verified by the Agency or any other authority. The content is subject to change without prior notice.Reproduction or further distribution of this information may be subject to copyright protection. Use of the information without obtaining the permission from the owner(s) of the respective information might violate the rights of the owner.
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