The effect of pressure on the dissociation constant of hydrofluoric acid and the association constant of the NaF ion pair at 25°C |
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Authors: | A. V. Usha Gordon Atkinson |
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Affiliation: | (1) Saudi Aramco, Dhaharan, Saudi Arabia;(2) Department of Chemistry, University of Oklahoma, 73019 Norman, OK |
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Abstract: | The effect of pressure on the dissociation constant of hydrofluoric acid was determined by using the indicator technique at 25°C at an ionic strength of 0.1m over a pressure range of 1 to 2000 atm. A value of 3.14 for pKa* at I =0 was obtained by extrapolation to zero ionic strength at 1 atm. The pressure dependence yielded a partial molar volume change of –9.6 cm3-mol–1 and a compressibility change of — 35×10–3 cm3-mol–1 –atm–1 for the dissociation. The dependence of ionic strength on the association constant KA* of NaF was studied at 25°C and 1 atm. Extrapolation to I=0 yielded a pKA* of –0.78. The pressure dependence of KA* gave a change of volume of 3.26 cm3-mol–1 and a change in compressibility of 6×10–3 cm3-mol–1-atm–1 for the formation of the ion pair. |
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Keywords: | Acid-base indicator association constant sodium fluoride ion pair partial molal volume and compressibility change |
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