On the Suitability and Validity of “Reference Electrolyte” Method for the Determination of Single Ion Thermodynamic Properties in Solutions

Abstract

Abstract Much advocated and supposed to be best method for the determination of the Gibbs energies of single ions in any solvent or Gibbs energies of transfer of single ions between two solvents (true for other thermodynamic properties as well) is based on thermodynamics of “reference electrolyte” TATB (tetraphenylarsoniumtetraphenylborate). TATB, composed of isoelectrical counter ions (TA+-tetraphenylarsonium ion Ph4As+ and TB – -tetraphenylborate BPh4 – ) with large hydrophobic groups of equal radii, has been assumed to have identical Gibbs energies of solvation in any solvent and hence can be split equally to get i) Gibbs energies of single ions in any solvent and ii) Gibbs energies of transfer of single ions between two solvents. However, all the extrathermodynamic methods including “reference electrolyte” method for the determination of single ion thermodynamic values, based on Born or modified Born equations and ionic additivity principles are defective and invalid from theoretical and practical points of view. All the single ion values in the literature are thus unreliable. Moreover, different theoretical and experimental facts make “Ph4AsBPh4” unsuitable for equal division of the Gibbs energies (in a solvent) or Gibbs energies of transfer (between two solvents) of the reference electrolyte into single ion values as reference standard to give single ion values of other ions. Single ion thermodynamic values in any solvent or between two solvents are illusive and only the electrical components of the single ions can be determined but not without limitations.