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Please be aware that this old REACH registration data factsheet is no longer maintained; it remains frozen as of 19th May 2023.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

Link to relevant study record(s)

Description of key information

According to REACH Annex XI Section 2, study is not relevant for a water based multi constituent substance containing inorganic dissociated and ionised compounds.

Key value for chemical safety assessment

Additional information

Table 1. Dissociation constants of constituents.

Ion  pKa
CO32-  10.33
HCO3-  6.35
 S2-  11.96
 HS-  7.04

Sodium hydroxide dissociates completely.


UNEP OECD (2002), SIDS Initial Assessment Report for SIAM 15: Sodium carbonate, available in:


UNEP OECD (2002), SIDS Initial Assessment Report for SIAM 14: Sodium hydroxide, available in:

WHO (1981) IPCS International Programme on Chemical Safety, Environmental Health Criteria 1:, Hydrogen sulfide, available in: