The Dissociation Equilibria of Trioxochlorochromate(VI) and Chromic Acid

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

“…Similar condensation reactions occur between Cr(VI) and anions of other acids, e.g., HCl, ,, H 2 SO 4 , and H 3 PO 4 , and species such as CrO 3 Cl - , CrSO 7 2- , and HCrPO 7 2- are formed. ,,, …”

“…The principal equilibria in a Cr(VI) solution are 55 with K 12 ) (3.4-5.0) × 10 14 at 25 °C; 43,50 with K a2 ) (2.82-3.16) × 10 -7 at 25 °C; 39,50 and, in strongly acidic solutions, with K a1 ) 1.5 at 20 °C. 55,56 Also, higher polychromates can be formed at high Cr(VI) concentrations in very strongly acidic media: 49 Similar condensation reactions occur between Cr(VI) and anions of other acids, e.g., HCl, 37,38,50 H 2 SO 4 , 37 and H 3 PO 4 , 57 and species such as CrO 3 Cl -, CrSO 7 2-, and HCrPO 7 2are formed. 37,38,50,57 All the Cr(VI) species listed above absorb light in the visible and ultraviolet regions due to charge-transfer transitions from orbitals localized mainly on the ligand atoms to an orbital localized mainly on Cr.…”

“…55,56 Also, higher polychromates can be formed at high Cr(VI) concentrations in very strongly acidic media: 49 Similar condensation reactions occur between Cr(VI) and anions of other acids, e.g., HCl, 37,38,50 H 2 SO 4 , 37 and H 3 PO 4 , 57 and species such as CrO 3 Cl -, CrSO 7 2-, and HCrPO 7 2are formed. 37,38,50,57 All the Cr(VI) species listed above absorb light in the visible and ultraviolet regions due to charge-transfer transitions from orbitals localized mainly on the ligand atoms to an orbital localized mainly on Cr. 32 Figure 1 shows the spectra of 2.50 × 10 -4 M K 2 Cr 2 O 7 in different media.…”

“…[25][26][27][28][29] Hexavalent chromium appears to be an ideal candidate for direct spectrophotometric study without an indicator, since all the Cr-(VI) species absorb light in the UV and visible regions. 32 This method [33][34][35][36][37][38][39][40][41][42][43][44] and others [45][46][47][48][49][50][51] have been used to study acid-base equilibria of Cr(VI) at 20 °C or slightly elevated temperatures. However, the potentiometric study by Palmer and co-workers 50 is the only high-temperature study (to 175 °C) of Cr(VI) equilibria.…”

“…UV−vis spectroscopy is limited to equilibria involving species containing appropriate chromophores. , Recently, stable pH indicators have been developed for temperatures up to 400 °C. − Hexavalent chromium appears to be an ideal candidate for direct spectrophotometric study without an indicator, since all the Cr(VI) species absorb light in the UV and visible regions − and others − have been used to study acid−base equilibria of Cr(VI) at 20 °C or slightly elevated temperatures. However, the potentiometric study by Palmer and co-workers 50 is the only high-temperature study (to 175 °C) of Cr(VI) equilibria.…”