Densities and compressibilities of aqueous sodium carbonate and bicarbonate from 0 to 45°C

The densities and the sound speeds of aqueous NaHCO₃ and Na₂CO₃ solutions were measured from 0.05 to 1.0m and from 0 to 45°C. These data were fitted to functions of molality and temperature and were used to calculate the apparent molal volumes V_? and compressibilites κ_φ of these solutions. Polynomial expression for V_? and κ_φ as functions of molality and temperature have been determined. The partial molal volumes and compressibilities of these solutions and literature data have been used to determine the volume ΔV and compressibility Δκ changes for the ionization of carbonic acid in aqueous solutions. These values of ΔV and Δκ have been used to estimate the effect of pressure on the ionization constants for carbonic acid from 0 to 45°C. The calculated pressure coefficients are in good agreement with the measured values.