A Potentiometric Study of the Reduction by Ferrous Ions of Potassium Iodate in Phosphoric, Sulphuric and Hydrochloric Acid Solutions

Physical Chemistry Laboratory, Department of Chemistry, Patna University, Patna 800005 Manuscript received 5 September 1974; accepted 21 February 1975 Potassium iodate can be accurately titrated potentiometrically with ferrous ion in phosphoric and sulphuric acid solutions over a wide range (8 N to 30 N) of sufficiently high concentration, the reduction proceeding directly to iodine. Titration is also possible in hydrochloric acid solutions, bat the mechanism of the reduction process is no longer given by the equation IO3-+ 5Fe2++ 6H+ = \(\frac{\mathrm 1}{\mathrm 2}I\)2+3H2O+5Fe3+ Two inflexions in the titration curve correspond to the initial reduction of iodic acid almost quantitatively to ICI8, and it subsequent reduction to ICI. The second inflexion at about 3.5 moles however, is not sharp and appears before the required amount of 4 moles of titrant has been added