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Please be aware that this old REACH registration data factsheet is no longer maintained; it remains frozen as of 19th May 2023.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

Physical & Chemical properties

Dissociation constant

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Administrative data

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Description of key information

The substance is a UVCB, dissociation constant is not applicable for a UVCB. Its representative component Ammonium sulfate has three dissociation constants at 25°C:
[sulfuric acid /hydrogen sulfate]: -3
[hydrogen sulfate /sulfate]: 1.92
[ammonium /ammonia]: 9.21
In aqueous solution, ammonium sulfate is completely dissociated into the ammonium ion (NH4+) and the sulfate anion (SO42-). Ammonia may however become a relevant form at basic environmental pH (8 to 9).

Key value for chemical safety assessment

Additional information

ECHA’s webinar “How to bring your registration dossier in compliance with REACH - Tips and Hints - Part 5 - Dissociation constant” (12 February 2014), indicates that “For complex mixtures (e.g. UVCBs*) estimation of the representative constituent’s pKa values, if appropriate, should be considered.” Indeed, the pKa of a component is a chemical constant (at a given temperature) which is independent of the other components present in the substance.

The dissociation constants of the representative constituent of the UVCB, ammonium sulfate, are known from peer-reviewed literature: OECD SIDS Initial Assessment Report - AMMONIUM SULFATE CAS N°: 7783-20-2, October 2004. These data respect all three conditions of Annex XI, § 1.1.1 (Use of existing data):

1) They are relevant for the registered substance since, as justified above, the pKa of Ammonium sulfate stays the same when this component is inside a UVCB; pKa value is not used in classification criteria; no exposure/risk assessment is required for the UVCB.

2+3) The data have been considered valid and sufficiently documented by the OECD SIDS experts (Advisory Committee on Existing Chemicals of the Association of German Chemists) who peer-reviewed it.

Therefore, the data on Ammonium sulfate adequately fill the data requirement on the UVCB.