Ion conductance and association studies of KI and some reference electrolytes KBPh₄, Ph₄AsI and <i>n-</i>Bu₄NI in acetonitrile, N,N-dimethyl formamide and their isodielectric binary mixtures at 298.15K^†

Abstract

The equivalent conductances (Λ) of some potential electrolytes e.g. KI, KBPh₄, Ph₄AsI and <i>n- </i>Bu₄NI where Ph = phenyl and <i>n-</i>Bu= <i>n-</i>butyl<i>, </i> have been measured in acetonitrile (ACN), N,N-dimethylformamide (DMF) and their iso-dielectric binary mixtures at 298.15K. The equivalent conductance at infinite dilution (Λ_o) and ion-association constant (<i>K</i>_A) for each of the solvent-electrolyte pairs have been evaluated from the data by computation using extended Fuoss-Hsia equation for the associated electrolytes, using a least .squares program. Λ₀ values are then dissected into ionic contributions λ₀ (i) by using two propositions:(1) reference electrolyte assumption: λ₀(Ph₄As⁺)=λ₀(Ph₄B^-) = 1/2 Λ₀(Ph₄AsBPh₄) and (2) Krumgalz's assumption: <i>₀(<i>n-</i>Bu₄N⁺) <i>η</i>₀ = 0.213 for all the solvents. The results obtained from the two methods are found to be in good agreement with each other. In order to understand the change of the association constants with solvent composition the transfer free energies (<img src='/image/spc_char/delta.gif' border=0><i>G</i><img src='http://www.niscair.res.in/jinfo/equation30.gif' border=0>) of the ion-association complex are evaluated from the <img src='/image/spc_char/delta.gif' border=0><i>G</i><img src='http://www.niscair.res.in/jinfo/equation30.gif' border=0> values of the constituting ions as obtained from the literature. The overall ion-association processes are explained not only in terms of the stability of the constituting ions but also due to that of the association complex in the physico-chemical framework of the solvent-system concerned