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Please be aware that this old REACH registration data factsheet is no longer maintained; it remains frozen as of 19th May 2023.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

This property is important for ionisable organic substances, since it indicates which chemical species will be present at a particular pH (e.g. in fresh or marine waters, or in the gut). The fate (e.g. water solubility, adsorption and bioconcentration potential) and toxicity of the ionised form of a substance may be markedly different from the corresponding neutral molecule. (Guidance on information requirements and chemical safety assessment - Chapter R.7a: Endpoint specific guidance).
According to ECHA Guidance on information requirements and chemical safety assessment the dissociation constant is irrelevant if the substance cannot dissociate due to a lack of relevant functional groups. According to Column 2 of REACH Annex IX (standard information requirements for substances manufactured or imported in quantities of 100 tonnes per year or more) of Regulation (EC) No 1907/2006, a study on dissociation does not need to be conducted if it is scientifically not possible to perform the test.
Sulphuric acid, compound with graphite is an inorganic solid, consisting of natural graphite and variable amounts of intercalated sulphuric acid. Graphite, being the main constituent of the substance, is naturally-occurring, insoluble in water and does not contain functional groups that dissociate. The incorporated sulphuric acid is partially leached out by water and dissociates into the environmentally ubiquitous sulphate (SO42-) and hydronium (H3O+) ions.
According to the SIDS Initial Assessment Report for sulphuric acid the pKa constant was determined to 1.92.
Due to the inherent properties of graphite, determination of the dissociation constant of sulphuric acid, compound with graphite is technically not feasible and therefore testing is not required under Regulation (EC) No 1907/2006 (REACH).

Key value for chemical safety assessment

Additional information