The Effect of Pressure on the Ionization of Water at Various Temperatures from Molal-Volume Data

The apparent molal volumes of dilute (0.002 to 1.0 m) aqueous HCl and NaOH solutions have been determined at 0, 25, and 50 degrees C and NaCl solutions at 50 degrees C The partial molal volumes ((V) over bar) of HCl, NaOH, and NaCl solutions have been determined from these apparent molal volumes and other reliable data from the literature. The partial-molal-volume changes (Delta(V) over bar (1)) for the ionization of water, H(2)O -> H(+) + OH(-), have been determined from 0 to 50 degrees C and 0 to 1 m ionic strength from the partial molal volumes of HCl, NaOH, NaCl, and H(2)O. The partial molal compressibilities ((K) over bar for HCl, NaOH, NaCl, and H(2)O have been estimated from data in the literature and used to determine the partial molal compressibility changes (Delta(K) over bar (1)) for the ionization of water from 0 to 50 degrees C and 0 to 1 m ionic strength. The effect of pressure on the ionization constant of water has been estimated from partial-molat-volume and compressibility changes using the relation RT ln(K(P)/K) = -Delta(V) over bar (P - 1) + 1/2 Delta(K) over bar (P - 1)(2) from 0 to 50 degrees C and 0 to 2000 bars. The results agree very well with the directly measured values.