Infrared titration of aqueous sulfuric acid

This paper presents the infrared (IR) titration of aqueous sulfuric acid solutions (0.50 M) obtained by the attenuated total reflection (ATR) sampling technique. After subtracting the water spectra, the spectra of the ionic species of H2SO4 in the 0-14 pH range were separated by factor analysis (FA) which also gave their abundance. The results were in agreement with the theoretical calculation of the distribution of the species. Three sulfate species were found: HSO4-, SO42-, and HSO4-/HCl. The latter stands for the bisulfate-hydronium complex formed by the addition of HCl to obtain measurements in the 0-0.47 pH range. For 0.50 M sulfuric acid, the comparison between the experimentally IR-determined quantities and the theoretical values gave a mean activity coefficient of 0.12 +/- 0.04, a value comparable to that from electrochemical measurements. Three types of water were quantitatively determined in the solutions: acidic water, basic water, and neutral water. The latter is always present while the two others are present in the low and high pH range, respectively. Another type of water strongly associated with the sulfates is also present. Moreover, knowledge of the behavior of the different types of water as the titration proceeded permitted us to give the details of the neutralization reactions of aqueous sulfuric acid by sodium hydroxide.