'Primary' hydration numbers of the hydrohalic acids and equilibrium constants of their resolvation using the emf method

The expression for the standard electromotive force, ^sE_N⁰, of the cell H₂|HX, H₂O + R|AgX,Ag as a function of the mole fraction N_R of the cosolvent R at low N_R values is used to determine the 'primary' hydration number, v, and the equilibrium constants for the resolvation of the ions of the hydrohalic acid HX. This method yields (at N_R → 0) v = 2 and practically no resolvation of the hydrogen ion for all HX (X = Cl, Br and I) and all the solvents examined. For monohydric alkanols and ether-alcohols the chloride anion is also not resolvated. For other cosolvents and for bromide and iodide anions, the equilibrium constants for the resolvation are determined and rationalized in terms of the species formed.