Structure and dissociation of the hydrogen sulphate ion in aqueous solution over a broad temperature range: A Raman study

Raman spectra of aqueous ammonium hydrogen sulphate solutions were measured over a temperature range from 0 to 330 degrees C at the liquid-vapour saturation curve. The hydrogen sulphate ion is virtually the dominant species above 250 degrees C, whereas at 0 degrees C the sulphate is the dominant species. Above ca. 250 degrees C and at dilute solutions the OSO3 unit of the HSO4- anion has C-3 nu symmetry. In concentrated H4HSO4 solutions and in the melt (m.p. 149 degrees C) nu(3)SO(3) (HSO4-) shows noncoincidence of the isotropic and anisotropic Raman frequencies (intermolecular coupling), indicating a formation of H bonded dimers or higher associates. Quantitative Raman measurements over the temperature range from 0 to 330 degrees C using S values (relative scattering coefficients) for sulphate and hydrogen sulphate gave the dissociation quotient for the second dissociation step of sulphuric acid. Log K-2 and Delta H-0 values were derived at I=0 in the temperature range from 0 to 330 degrees C.