Hexachlorotellurate(IV) hydrolysis equilibria in hydrochloric acid. Measurement by Raman and 125Te NMR spectroscopy and a reconsideration of earlier spectrophotometric results

Abstract

Solutions of TeO2 (0.001 M) in HCl over a range of concentrations are shown to contain TeCl2(OH)2 in addition to TeCl62−and TeCl4(OH)−. The hydrolysis constants for TeCl62− and TeCl4(OH)− have been determined from a reconsideration of earlier UV-visible spectrophotometric results (1)[Formula: see text]The hydrolysis constants have also been determined by quantitative Raman spectroscopy (K1 = 2.21 (± 0.16) × 104 M3; K2 = 442 ± 57 M3). The agreement between K2 determined by the two methods is good but K1 from spectrophotometry is much larger than that from Raman studies. This disagreement is attributed to ion-pairing which will be significant at the concentration at which the Raman measurements were made (c(TeO2) = 0.50 M). The hydrolysis constant for TeCl62− was also determined from the 125Te NMR spectra of TeO2/HCl solutions, which consisted of one signal, indicating rapid Te exchange between all species. The hydrolysis constant, determined in this way (K1 = 1.92 (± 0.07) × 104 M3) was also low compared to that determined from spectrophotometry. Key words: solution, equilibria, tellurium, hydrochloric acid, Raman spectroscopy, 125Te NMR spectroscopy, UV–visible spectrophotometry.