Journal of Solution Chemistry

, Volume 17, Issue 10, pp 987–997

Dissociation constants of phosphoric acid at 25°C and the ion pairing of sodium with orthophosphate ligands at 25°C

  • Dennis R. Migneault
  • R. Ken Forcé


The first and second acidity constants of phosphoric acid were determined in a 0.70 ionic strength solution of both a sodium and a potassium ion background salt at 25°C. These experimentally determined constants were compared to literature values as well as values calculated from a theoretical model. Assuming negligible ion pairing of the phosphate ligand with the potassium ions, the stability constants of the NaHPO4- and NaH2PO40 complexes were determined to be 1.3±0.3 and 0.49±0.07 (mol-L−1), respectively. These constants were used to model the speciation of orthophosphate in a background of a sodium salt from pH 3 to 10.

Key words

Sodium phosphate phosphoric acid dissociation constants marine systems 


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Copyright information

© Plenum Publishing Corporation 1988

Authors and Affiliations

  • Dennis R. Migneault
    • 1
  • R. Ken Forcé
    • 2
  1. 1.The Connecticut Agriculture Experiment StationNew Haven
  2. 2.Department of ChemistryUniversity of Rhode IslandKingston

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