First Dissociation Constant of Phosphoric Acid at a Number of Temperatures

Department of Chemistry, Science College, Patna University, Patna-800 005

Manuscript received 21 February 1981, accepted 11 March 1982

Tile pK₁ values of H₃PO₄ from 273.15 to 323.15 K have been recalculated from Nims as well as Bates data with the laelp of modified Davies equation. The difference in the pK₁ values has been largely reconciled. At 308.15 K, pK₁ has also been measured using Na-salt instead of K-salt. There is almost no difference in the values of pK₁ found. Bates had come to the conclusion that cells similar to Nims, where m_KH2PO4 : m_HCl lie between 1 and 3, or when pH is <3.0, do not give accurate pK₁ values. Using modified Davies equation, cells with pH values <3.0 gave reliable pK₁ values.