Determination of ratios of sulfate to bisulfate ions in aqueous solutions by Raman spectroscopy

Raman spectra are presented for aqueous ammonium bisulfate and zinc sulfate-sulfuric acid solutions over a wide range of concentration and from 20 to 85°C. The heights of the 980 cm^–1 (primarily SO₄^–2) and 1053 cm^–1 (primarily HSO₄^–) bands are correlated with the pH of the solutions. The ratio of the species SO₄^–2 and HSO₄^– can be obtained from the ratio of scattering intensities at 980 and 1053 cm^–1. The H obtained from plots of the log of the concentration products versus 1/T is –37±5 kJ-mol^–1 for ammonium bisulfate solutions and –48±4kJ-mol^–1 for the ZnSO₄-H₂SO₄ solutions. This compares to –22 kJ-mol^–1 for the H of bisulfate ion dissociation as obtained from thermodynamic equilibrium constants.