The solubility of Cr2O3(s) in (1
and 6) mol
kg–1 sodium hydroxide solutions has been investigated
at 25 °C. Even after 75 days of solid/solution contact the apparent
solubility continued to increase slowly. Analysis of the solution
phase by UV–vis spectrophotometry revealed that all of the
dissolved chromium was present as Cr(VI), in the form of CrO4
2–(aq); no Cr(III) could be detected. Consistent
with this finding, Cr(III) dissolved in 6 mol kg–1 NaOH was found to be oxidized to CrO4
2–(aq) over of period of days. No significant changes to the solid
phase, Cr2O3(cr), were found, either by X-ray
diffraction or by X-ray photoelectron spectroscopy, as a result of
its contact with NaOH(aq). Both CrO4
2– and Cr(III) were found to be unreactive toward a range of organic
and inorganic compounds in 6 mol kg–1 NaOH over
many days at ambient temperatures. However, CrO4
2– catalyzed the decomposition of L-ascorbate, and
was rapidly reduced by elemental Zn to Cr(III) in NaOH(aq).
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