THE CR2O72--CRO42--HCRO4- SYSTEM REVISITED

The electronic spectra of aqueous Cr-VI solutions in the pH range 3-11 have four isosbestic points, located at 246, 293, 338 and 441 nm. The se positions are independent of the total concentration of Cr-VI. The existence of the isosbestic points indicates that only two species are present, namely CrO42- and Cr2O72-, and that HCrO4- is spectrophotome trically undetectable. This conclusion is further supported by factor analysis, which gives the number of linearly independent species in so lution to be two, and also by the method of spectral displacement. At the isosbestic points absorbance is linear in total Cr-VI concentratio n. In this sense Beer's law is valid, and the results can be used for analytical purposes. Copyright (C) 1996 Elsevier Science Ltd