Measurement of the apparent dissociation constants of hydrofluoric acid in concentrated electrolyte environments and their relationship to the thermodynamic value

The notable presence of fluoride in African rift valley salt lakes has important hydrochemical and mineralogical implications. We have studied the fluoride equilibria to determine apparent Ka values for HF by the method of Vanderborgh over an extended range of ionic strengths covering the lake-like electrolyte environments of interest in a target lake, The apparent pKa values of 2.990, 2.929, 2.820 and 2.739 were obtained for ionic strengths of 0.266, 0.584, 1.024 a;ld 1.419 respectively. When extrapolated to infinite dilution (zero ionic strength), these yield the thermodynamic Ka value of 7.07x10(-4) which is in good agreement with other literature values.

G MHINZI ,D MOSHA ,Q QULWI ,