Theory of potentiometric rotating disc electrode technique for investigating iodate-iodide kinetics

Abstract

The iodate-iodide reaction in 1 M aqueous perchloric acid medium was investigated by the galvanostatic rotating disc electrode technique at 25 +± 0.5°C. The ionic strength of the solutions was maintained at unity. The potential-current curves were characterized by: (a) In the absence of iodate, the I2 + 2e- .2I- redox system was confirmed to be transport controlled and reversible in a concentration range of iodine 2.65 - 1.05 mM and rotation speeds 27 - 144 rpm. (b) In the presence of iodate, the electrode potentials depended upon the concentrations of the iodine and iodide species in the thin layer immediately adjacent to the platinum electrode surface. The reaction was confirmed to be a heterogeneous process in a concentration range of iodine 0.3 - 1.0 mM and iodate 5 - 30 mM. The reaction orders with respect to iodide and iodate have been confirmed to be 1.5 and 1 respectively.