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 re dox reactions such as chromium(VI) and iron(III) with cobalt(II). In t he 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)/F e(II) systems. Two large potential breaks are thus observed at equival ence points when the titration of 5 x 10(-4) mol dm(-3) chromium(VI) a nd 1 x 10(-3) mol dm(-3) iron(III) with cobalt(II) is carried out in t he presence of 8 x 10(-2) mol dm(-3) phen at pH 1, while in the absenc e of this ligand no potential break can be observed at equivalence poi nts. By using these redox reactions, we propose successive potentiomet ric titrations of chromium(VI) and iron (III) with cobalt(II) in a sin gle titration. The proposed method is successfully applied to the dete rmination of chromium and iron in high carbon ferrochromium.