Application of Differential Electrolytic Potentiometry to the Titration of Iodate Ion with Ferrous Ion in Different Acid Solutions

Physical Chemistry Laboratory, Department of Chemistry, Patna University, Patna 800 005 Manuscript received 7 September 1976, revised 17 October 1977, accepted 16 January 1978 Differential electrolytic potentiometry of the reaction between potassium iodate in hydrochloric, sulphuric and phosphoric acid solutions and ferrous ion is reported in this communieation. Accurate titratious are possible Ia the three acid solutions of moderate concentrations, but the mechanism of reduction of IO3 - by Fe2+ appear to be different in each. In hydrochloric acid solutious, the differential titration curves show one single peak corresponding to the formation of ICl3. In sulphuric and phosphoric acid solutions the number of peaks in the titration curve increase to two and three respectively, indicating intermediate formation of I2+ species in both, which is subsequently reduced to iodine. In phosphoric acid, iodine is further reduced and the third peak indicates the reduction of iodate ion ultimately to iodide ion. An additional peak appears when the titrations in sulphuric and phosphoric acid solutions are carried out in presence of potassium chloride. This peak at 4 moles of titrant corresponds to the formation of ICI during the course of reduction. Optimum conditions for the titrations are discussed