Successive potentiometric titration of chromium(VI) and iron(III) with cobalt(II) in the presence of 1,10-phenanthroline

Studies are made on the effect of 1,10-phenanthroline (phen) on the redox reactions such as chromium(VI) and iron(III) with cobalt(II). In the presence of phen, the conditional redox potential of the Co(III)/Co(II) system is lower than that of the Cr(VI)/Cr(III) and the Fe(III)/Fe(II) systems. Two large potential breaks are thus observed at equivalence points when the titration of 5 x 10(-4) mol dm(-3) chromium(VI) and 1 x 10(-3) mol dm(-3) iron(III) with cobalt(II) is carried out in the presence of 8 x 10(-2) mol dm(-3) phen at pH 1, while in the absence of this ligand no potential break can be observed at equivalence points. By using these redox reactions, we propose successive potentiometric titrations of chromium(VI) and iron (III) with cobalt(II) in a single titration. The proposed method is successfully applied to the determination of chromium and iron in high carbon ferrochromium.