Activity coefficient of sulfuric acid measured using infrared titration

The titration of sulphuric acid by infrared spectroscopy using the attenuat ed total reflection (ATR) technique was made in the 0 to 14 pH range for so lutions ranging from 1.89 to 0.01 M. The subtraction of the water spectrum was made using acidic, neutral, and basic waters which exhibit different sp ectra. The results gave the spectra of mixtures of the HSO4- and SO42- ioni c species in solutions. For each concentration, factor analysis (FA) sorted the spectra of the pure ionic species and gave through the multiplying fac tors (MF) the distribution of the species as a function of pH. This distrib ution is the same as that obtained from the equilibrium equations. The IR m easurements gave directly the ratios of the activity coefficients of HSO4- and SO42- ions. This ratio varies with the total concentration of both ions but is independent of the relative concentration. The fitting of the exper imental and theoretical volumetric titration curves in the high and low pH regions gave the mean activity coefficients of the other species present in the solutions. The values obtained are comparable to those obtained by ele ctrochemical measurements. These results show that it is possible to use IR spectroscopy to study aqueous solutions of inorganic acids from low to hig h concentrations.