Precise coulometric titration of cerium(IV) as an oxidising agent with electrogenerated iron(II) and reliability in cerium(IV) standardisation with sodium thiosulfate

摘要

Cerium(IV) is a useful strong oxidising agent and is often standardised against thiosulfate. In the standardisation, triiodide liberated by Ce(IV) in an acidic potassium iodide solution can be titrated with thiosulfate to determine the concentration of Ce(IV). The accuracy of the standardisation has not been established because the iodine liberation process is not well-understood. In the present study, to evaluate the iodine liberation process, Ce(IV) was assayed through two different methods: precise coulometric titration with electrogenerated ferrous ions and gravimetric titration with thiosulfate independently determined by precise coulometric titration with electrogenerated iodine. The reliability of Ce(IV) standardisation with thiosulfate is discussed on an absolute basis by coulometric titrations of both Ce(IV) and thiosulfate solutions. Finally, the accurate determination of Ce(IV) was achieved by both methods. Information on the stability of Ce(IV) solutions is also presented.