POTENTIOMETRIC AND SPECTROPHOTOMETRIC STUDY OF THE ACID-BASE EQUILIBRIA OF CR(VI) AT 25-DEGREES-C AND DIFFERENT IONIC STRENGTHS OF AQUEOUS KNO3

The hydrolysis of the chromate ion has been studied using a potentiome tric-spectrophotometric automated titration system, titrating basic K2 CrO4-KNO3 solutions with previously standarized HNO3-KNO3 solutions. T he temperature was kept constant at 25-degrees-C and the ionic strengt hs were 0.5, 1.0 and 2.0 mol-dm-3. The resulting titration curves can be interpreted in terms of two equilibria involving the formation of H CrO4-(aq) and Cr2O72-(aq). A spectrophotometric batch study was also c arried out in order to obtain the thermodynamic constant for the HCrO4 -(aq) formation as well as the spectrophotometric parameters at low io nic strengths. The proposed stoichiometric constants for the two react ions and the molar absorptivities for the three species at different w avelengths and ionic strengths are also given.