UV−Vis Spectroscopic Determination of the Dissociation Constant of Bichromate from 160 to 400 °C

Abstract

On the basis of direct measurements by UV-vis spectroscopy, the dissociation constant of bichromate was found to decrease with temperature from 160 to 400 °C. For fixed Cr(VI) and KOH concentrations, the molal concentration of HCrO 4initially increases with temperature but decreases again in the vicinity of water's critical point, where the density decreases substantially. The decrease in HCrO 4at high temperature and low density may be attributed to (K + )(CrO 4 2-) ion pairs, to a high degree of electrostriction about CrO 4 2-, which facilitates the reaction HCrO 4 -+ OH -) CrO 4 2-+ H 2 O, and to ion activity coefficients.

High‐throughput screening of pKa values of pharmaceuticals by pressure‐assisted capillary electrophoresis and mass spectrometry

“…The most common method for measuring pK a is titration using either potentiometric or UV spectral detection 3–6. However, certain drawbacks and limitations of these methods have been recognized, e.g., the potentiometric titration method requires 1–2 mg of pure substance and a high substance concentration of ca.…”

Bismuth Oxyhalide Induced Growth of Pt Nanoparticles within Mesoporous Alumina Films and their Use as Reusable Catalyst for Chromium(VI) Reduction

“…The reduction of Cr VI was monitored by recording UV–visible absorption spectra of the mixed solution at certain time intervals. The spectral evolution in the range of 240−500 nm is shown in Figure a, which can be ascribed to the ligand (oxygen) to metal (Cr VI ) charge transfer transition of Cr 2 O 7 2− . As previously reported, the reduction of Cr VI is highly dependent on the pH of the solution and the rate of reduction becomes slower with increase in pH of the solution.…”

Fabrication of Metal‐Nanoparticle‐Modified Semiconducting Copper– and Silver–TCNQ Materials as Substrates for the Reduction of Chromium(VI) Using Thiosulfate Ions at Ambient Temperature

“…Figure 4 A shows time‐dependent UV/Vis spectra for CuTCNQ/Pt with thiosulfate ions and Figure 4 B for CuTCNQ/Pt with formic acid. It is clear that the absorbance maximum at 350 nm owing to the ligand‐to‐metal charge transfer of dichromate ions14 decreases in intensity with time, thus indicating the reduction of Cr VI to Cr III . UV/Vis spectra were collected for all samples at 20 °C for 2 h and the absorbance at 350 nm for each time point was measured.…”