Échelle d'acidité dans l'hydrogénodifluorure de potassium (KHF2) fondu à 250°C: Détermination électrochimique |
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| Authors: | J Devynck B Trémillon M Sloim H Ménard |
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| Institution: | 1. Laboratoire d''Electrochimie Analytique et Appliquée (associé au C.N.R.S.)., Ecole Nationale Supérieure de Chimie de Paris, Université Pierre et Marie Curie, France;2. Laboratoire de Chimie Analytique, Institut National des Sciences et Techniques Nucléaires, Saclay (France) |
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| Abstract: | In molten potassium hydrogenodifluoride (KHF2) fully ionized into K+ and HF2?, at 250°C, the HF2? ion is slightly dissociated according to the equilibrium: HF2?HF+F?. This is a solvent acid base equilibrium, HF being the strongest acid and F? the strongest base in this system. By means of a voltammetric study we showed that the hydrogen electrode may be used as an acidity indicator electrode in the whole acidity range of the melt. By analysis of the equilibrium potential variation in acidic and in basic media, the HF2? dissociation constant (melt autoprotolysis constant): KD = {HF} {F?} was determined The experimental value: KD=10?2.05 mol2 kg?2 is compared with a calculated one, issued from thermodynamic data. Results obtained with other electrodes (LaF3 monocrystal electrode and copper electrode) were discussed and compared with those obtained with the hydrogen electrode. |
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