Raman spectroscopic investigations of the CrO 4 2− /Cr 2 O 7 2− equilibrium in aqueous solution

With the intention of doing a study of the CrO   4 2− /Cr 2 O   7 2−equilibrium in aqueous solution, we have carefully re‐examined the Raman spectra of CrO   4 2− , Cr 2 O   7 2−and ClCrO   3 − . Diluting stepwise an aqueous solution of CrO   4 2−ion we have showed the non‐existence of the HCrO   4 −species which was previously considered to exist in such systems. By studying the effect of pH on the Raman spectra we calculated the constant for the equilibrium: 2 CrO   4 2−+ 2H + ⇌ Cr 2 O   7 2−+ H 2 O to be log β 22 =13.77±0.02 (20°C and KNO 3 0.8 M). Using this value of the constant, we were able to establish the distribution diagram of the CrO   4 2−and Cr 2 O   7 2−species versus pH.