Abstract
Potentiometry of electrochemical cells equipped with ionic liquid salt bridge (ILSB) has been studied and applied for determination of the solubility in water of a sparingly soluble ionic liquid (IL) employed for the ILSB consisting of B + and A − , and also the mean activity coefficient of the chloride salt of the IL-constituting cation, BCl. In the case of an electrochemical cell with ILSB made of BA sandwiched by two electrolyte solutions, one containing only hydrophilic ions and the other containing BCl, the cell voltage, E cell , involves the term of the solubility of the IL, enabling the potentiometric determination of the solubility of BA in water based on the Debye-Hückel limiting law. Experimentally, from measured E cell values the solubility of tributyl(2-methoxyethyl) phosphonium bis(pentafluoroethanesulfonyl) amide ([TBMOEP + ][C 2 C 2 N − ]) is determined to be 0.15 mmol dm −3 at 25 °C. The value obtained is of thermodynamic nature because it does not involve the activity coefficient terms. An estimated value of the mean activity coefficient of tributyl(2-methoxyethyl) phosphonium chloride (TBMOEPCl) in aqueous 0.0093 M TBMOEPCl, 0.88 ± 0.01 at 25 °C, agrees with 0.87 ± 0.02 in aqueous 0.01 M TBMOEPCl obtained by the cell in which the ILSB is sandwiched by two aqueous TBMOEPCl solutions, suggesting the consistency in the present potentiometric approach.
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