Thermodynamic properties of aqueous solutions with citrate ions. Compressibility studies in aqueous solutions of citric acid

• Over a wide range of concentrations and temperatures sound velocities were measured in aqueous solutions of citric acid.
• Compressibility properties of citric acid solutions are thermodynamically characterized.
• Changes in the structure of water when citric acid is dissolved are discussed.

Sound velocities in aqueous solutions of citric acid were measured from 15 °C to 50 °C in 5 °C intervals, within the 0.1 mol · kg−1 to 5.0 mol · kg−1 concentration range. These sound velocities served to evaluate the isentropic and isothermal compressibilities, the apparent molar compressibilities, the isochoric thermal pressure coefficients, changes of the cubic expansion coefficients with pressure at constant temperature, the changes of heat capacities with volume and hydration numbers of citric acid in aqueous solutions.