Analytical Sciences

Evaluation of the Stability of Iron(II) Solutions by Precise Coulometric Titration with Electrogenerated Cerium(IV)

Toshiaki ASAKAI and Akiharu HIOKI

National Metrology Institute of Japan (NMIJ), National Institute of Advanced Industrial Science and Technology (AIST), Tsukuba Central 3, 1-1-1 Umezono, Tsukuba, Ibaraki 305-8563, Japan

An iron(II) solution is often used as a reducing agent in titrimetry and standardized with cerium(IV) or potassium dichromate. Such an iron(II) standard solution is needed for not only titrimetric analyses, but also instrumental ones. Iron(II) is unstable even in a highly acidic solution, mainly due to air-oxidation; therefore, its standardization is required before use. In the present study, the concentration of an iron(II) solution was accurately determined by coulometric titration with electrogenerated cerium(IV), and also by gravimetric titration with a standard potassium dichromate; new useful information concerning the stability of iron(II) solutions in aqueous sulfuric acid was obtained. The current efficiency of the coulometric titration with electrogenerated cerium(IV) was not very high; however, it was found that the titration efficiency was sufficient to assay an iron(II) solution.

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