10.8 : 酸化還元滴定: ヨウ素還元滴定法とヨウ素酸化滴定法

Iodometry and iodimetry are titrimetric methods used to analyze the amount of oxidizing or reducing agents present in a sample, respectively.

In iodometric titrations, the oxidizing analyte solution is typically acidified and treated with an excess of iodide ions, producing an equivalent amount of iodine in equilibrium with triiodide. The liberated iodine is then titrated against a standardized reducing agent.

A freshly prepared starch solution is added near the endpoint, forming an intensely dark blue starch–iodine complex. The titration then continues until the blue color disappears.

The stoichiometric relationship via iodine between the oxidizing analyte and reducing titrant enables the determination of the concentration of the analyte.

In contrast, iodimetric titrations involve direct titration of a reducing analyte in the presence of starch against a standard iodine solution until the solution turns dark blue, showing that all the analyte is oxidized and the starch–iodine complex is forming.

Knowing the reaction stoichiometry and volume of titrant consumed, the concentration of the analyte can be determined.