The apparent molal volume Vβ and adiabatic compressibility κβ of H3PO4, NaH2PO 4, Na2HPO4, and Na3PO4 have been determined from density and sound speed measurements in 0.725 m NaCl solutions at 25 °C. The partial molal volumes V̄i* and compressibilities κ̄i* have been determined by extrapolating the values of Vβ and κβ to infinite dilution in the NaCl media. The results have been compared to earlier measurements made on a number of electrolytes in NaCl media. The phosphate results showed correlations between the values of V̄i* and κ̄i* as found for other electrolytes. The values for the volume ΔVi and compressibility Δκ i changes for the dissociation of H3PO4 in 0.725 m NaCl have been calculated from the measurements. The calculated values of ΔVi and compressibility Δκi have been used to estimate the effect of pressure KP/K0 on the dissociation of H3PO4 in the oceans using RT ln[K P/K0] = -ΔViP + 0. 5ΔκiP2, where P is the applied pressure in bars. The results are in reasonable agreement with directly measured values.
ASJC Scopus subject areas
- Physical and Theoretical Chemistry
- Surfaces, Coatings and Films
- Materials Chemistry