Physico-chemical studies with aqueous fluoride solutions

Summary

The decomposition potentials of HF, LiF, NaF, KF, NH₄F, KHF₂, AgF, CdF₂ and SbF₃, and the cathode and anode discharge potentials of NH₄F, KHF₂, AgF, CdF₂ and SbF₃, in aqueous solution, have been determined at 25°C. at various concentrations using polished platinum electrodes. The current-voltage curves for LiF, NaF, KF, NH₄F and KHF₂ have an initial break at about 1·55±0·05 volts for each concentration, and another break at a higher potential which varies with the nature of the metallic ion, and also with the concentration of the fluoride solution. The curve for SbF₃ also has two breaks, each of which, however, varies with concentration. The curves for HF, CdF₂ and AgF have only one break each. Of the currentcathode potential and current-anode potential curves obtained, only the current-cathode potential curves for NH₄F, KHF₂ and SbF₃ have two breaks corresponding to the respective breaks in the decomposition current-voltage curves; the other curves have only one break each. These results have been discussed in detail and the inference is drawn that even alkali fluorides may have a true decomposition potential in aqueous solution.