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Please be aware that this old REACH registration data factsheet is no longer maintained; it remains frozen as of 19th May 2023.

The new ECHA CHEM database has been released by ECHA, and it now contains all REACH registration data. There are more details on the transition of ECHA's published data to ECHA CHEM here.

Diss Factsheets

Administrative data

dissociation constant
Data waiving:
study scientifically not necessary / other information available
Justification for data waiving:
the study does not need to be conducted because the substance is hydrolytically unstable (half-life less than 12 hours)
the study does not need to be conducted because the substance has no ionic structure
Justification for type of information:
In accordance with Section I of REACH Annex XI, the dissociation constant (required in Section 7.16) does not need to be measured as the registration substance itself does not have ionisable structural features.
The substance will totally dissociate into ions, and form different species, the pKa of the parent substance cannot be determined, and this study is not scientifically necessary:

Based on the basic knowledge of soluble aluminium slats, including aluminium sulphate, the form of the element in water varies from mononuclear to polynuclear hydroxo complex depending on the pH of solution:
Al3+→ [Al(OH) ]2+ → [Al(OH)2]+ → Al(OH)3(↓) → [Al(OH)4]- → [Al2O(OH)6]2-
pH < 4   →                 →                 →                 →                     → pH > 10
Due to physical-chemical properties (see section 4.8 water solubility), the substance dissolving in water results a strong acidic solution. Using the flask method , the water solubility of 202030/A at 20°C was ≥ 1000 g/l. The pH of the aqueous sample was 2.4. As a consequence in this aqueous solution, the Aluminium compound exists mainly as Aluminium ion and complexes of aluminium species [e. g. Al(OH)4-, the predominant species at higher pH], which are not expected to dissociate under naturally relevant pH (4-9) conditions.
In addition, in aqueous solution Al3+ does not occur as the free ion but is surrounded by six molecules of water to form (Al(H2O)6)3+. As pH increases, protons are removed from the co-ordinated waters to give various hydrolysis products. Progressive hydrolysis leads to the formation of aluminium hydroxide. Concentrated commercial products are stable over months and years. When applied AS hydrolyses within minutes to Al(OH)3.
Based on the study of hydrolysis of aluminium salts (see section 5.1.2 Hydrolysis), the process of polymeric aluminium species formation and decomposition was demonstrated.
Therefore the study of dissociation constant does not need to be conducted.

Data source

Materials and methods

Results and discussion

Applicant's summary and conclusion