VOLUMETRIC PROPERTIES OF, AND ION-PAIRING IN, AQUEOUS-SOLUTIONS OF ALKALI-METAL SULFATES UNDER SUPERAMBIENT CONDITIONS

Apparent molar volumes for Na2SO4(aq) and K2SO4(aq) have been obtained from our recent densitometric measurements and selected experimental data from literature at temperatures up to 573 K and pressures up to 3 0 MPa. The Fitter ion-interaction model was used to correlate the data in order to obtain recommended values as a function of temperature, p ressure and concentration and to yield partial molar volumes at infini te dilution. By comparison with the volumetric data of other strong el ectrolytes, and consistent with their reported ion-association constan ts, the present data indicate that ion-pairing is significant for Na2S O4(aq) and K2SO4(aq) at higher temperatures. A semiquantitative treatm ent is presented which enables the partial molar volumes of 1:2 (and 2 :1) electrolytes to be corrected for the effects of ion-pairing.