The Determination of Fluoride-Ion Activities in Moderately Concentrated Aqueous Hydrogen-Fluoride

Abstract

A lead-lead chlorofluoride electrode has been used to determine fluoride ion activities, a_F-, in 0-6 M aqueous HF. Our data show that a_F- increases, passes through a maximum and then decreases with increasing HF concentration. The conductivities of concentrated HF- water mixtures have also been measured. Both the conductometric and potentiometric data are used in the development of a quantitative model of the equilibria existing between fluoride ions and HF molecules in the solutions studied. The data support the view that the ions (HF)₂F^-, (HF)₃F^- and (HF)₄F^- are important species in moderately concentrated aqueous HF.