Some Observations on the Chemical Behavior of Iodine at Low Concentrations

Abstract

An investigation has been made of the chemical forms assumed by I¹³¹ initially in the form of iodide ion at low concentration (the order of 10⁻⁷M) when it is oxidized under various conditions. Oxidation at room temperature in 1f sulfuric acid solution by dichromate ion or cerium(IV) results in the formation of I₂ and three additional, unidentified, chemical fractions which are not readily exchangeable with I⁻, I₂, or IO₃⁻. Two of the unidentified fractions are extracted from aqueous sulfuric acid solution by organic solvents, one fraction being converted by aqueous sodium hydroxide to water‐soluble forms exchangeable with I₂. At least some of the unidentified fractions probably are the products of reactions between trace impurities, molecular or colloidal, and iodine in an oxidized reactive form such as HIO. These unidentified fractions are quite inert toward oxidation and reduction. When iodide ion at low concentration is treated with a hot sulfuric acid solution of cerium(IV), the principal product is IO₃⁻, or a species readily exchangeable with IO₃⁻. The IO₃⁻ formed in this way is readily reduced at room temperature to I⁻ by a sulfuric acid solution of iron (II).