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Physical & Chemical properties

Dissociation constant

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Description of key information

The dissociation constant of arsenic acid was considered to be pKa 1= 2.22, pKa 2 = 6.98 and pKa 3 = 11.53. 

Key value for chemical safety assessment

Additional information

Several sources provide pKa values for arsenic acid. Using a weight of evidence, the key value for the dissociation constant of arsenic acid on the different equilibrium in water was concluded using ATSDR (2007) report:

H3AsO4 <-> H+ + H2AsO4-           pKa 1 = 2.22

H2AsO4- <-> H+ + HAsO42-       pKa 2 = 6.98

HAsO42- <-> H+ + AsO43-            pKa 3 = 11.53