Haloselenate(IV) formation and selenous acid dissociation equilibria in hydrochloric and hydrofluoric acids

Abstract

Raman spectroscopy has shown that the initial stages of haloselenate(IV) formation equilibria are the same in HF and HC1 solutions.[Formula: see text]The constants K4 and K5, evaluated by quantitative Raman measurements, for HCl solutions are 0.015 (± 0.001) L2 mol−2 and 0.9 (± 0.1) × 10−5 L2 mol−2, respectively. These constants yield the minimum average deviation in normalized molar scattering intensity for the species formed in three regions of the spectra, 690 and 890 cm−1 (SeO stretching) and 100–450 cm−1 (deformation and SeCl stretching). Before the onset of haloselenate(IV) formation, changes in the SeO stretching band intensities with HX concentration occur due to repression of ionic dissociation of selenious acid[Formula: see text]Quantitative Raman measurements yield K1 = 9.8 (± 0.3) × 10−3 mol L−1. Reasons for the high value of this constant, compared to reported values, are discussed.