Abstract
The volumetric behavior of NaF(aq) and KF(aq) has been studied as a function of temperature up to 627 K and pressures up to 30 MPa using a vibrating-tube flow densitometer. The measured densities were used to derive apparent molar volumes VΦ at concentrations up to 0.9 mol-kg-1 for NaF and up to 3 mol-kg-1 for KF. Standard partial molar volumes V2o[(NaF)-and V2o((KF) were obtained by extrapolating VΦ values to infinite dilution using the Pitzer equation truncated at the second virial coefficient. Comparison with related 1:1 and 1:2 electrolytes allows examination of the extent to which the concentration and temperature dependence of the volumes is linked with the size and charge of ions. A semiquantitative estimate of association based on the close similarity of fluorides and hydroxides is made to evaluate the effect of ion-pairing on the volumetric behavior of the fluorides.
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