The ionization of perchloric and hydrofluoric acids in aqueous solution

Cyclical bifurcated hydrogen bonded structures are proposed for aqueous solutions of hydrofluoric acid and for the bifluoride ion which are consistent with the spectral data. The structure proposed for HF is also applicable to solutions in organic solvents. Raman spectra of tetramethylguanidinium perchlorate suggest that the corresponding Raman spectra of perchloric acid solutions may not be interpreted in terms of a completely dissociated acid. Other evidence including activity coefficient, heat capacity and partial molal volume data suggest that there is some association in relatively dilute perchloric acid solutions between the perchlorate ion and the hydrated proton. This association decreases in concentrated aqueous solutions.     

Excess enthalpy and entropy of aqueous tetramethylguanidinium methanesulfonate and trifluoromethanesulfonate solutions

Relative apparent molal heat contents, φ_L, are reported for the tetramethylguanidinium salts of methanesulfonic (MS) and trifluoromethanesulfonic (TFMS) acids. Relative partial molal heat contents, L?₂, are calculated and combined with previously reported activity coefficient data, to yield excess entropies. It is found that the values of L?₂ make the principal contribution to the excess entropies of Me₄GuMS solutions while the excess free energies, as calculated from activity coefficients, make the greatest contribution to the excess entropies of Me₄GuTFMS solutions.