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Dissociation constant

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Description of key information

Dissociation constant (EDTMP-xCaNa): EDTMP acid has four phosphonate groups, so eight ionisable protons from the substance acid form.

Key value for chemical safety assessment

Additional information

The dissociation constant of EDTMP-xCaNa is read across from its parent acid. Eight dissociation constants as listed below were obtained for the acid using an appropriate estimation method. The result is considered reliable and selected as key study.

pKa1 = 1.3
pKa2 = 2.7
pKa3 = 4.2
pKa4 = 5.7
pKa5 = 5.9
pKa6 = 7.3

pKa7 = 8.8

pKa8 = >10

Also, in a secondary source to which no reliability could be assigned, EDTMP-H has eight dissociation constants as listed below:





An approximate experimental determination, using stoichiometric titration and pH determination of aqueous solutions, has been conducted. This is considered to provide suitable and practical information, which is fit for purpose in the context of REACH chemical safety assessment. This data is reported in section 4.20.