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Dissociation constant

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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: