Iodometrie

Iodometrie is a form of redox titration where iodine is used as a titrant or is liberated as part of the reaction. It is a quantitative analytical method employed in chemistry to determine the concentration of specific substances. The principle relies on the reaction between iodine and a reducing agent, or conversely, the reaction of an oxidizing agent with iodide ions to produce iodine.

There are two main types of iodometry: direct iodometry and indirect iodometry. In direct iodometry, iodine is directly used as the titrant. A common example is the titration of a reducing agent, such as thiosulfate ions, with a standard iodine solution. The endpoint is typically detected using starch as an indicator, which forms a deep blue complex with iodine. As the thiosulfate is added, it reduces the iodine, and at the endpoint, the blue color disappears.

Indirect iodometry, also known as iodimetric titration, involves the liberation of iodine from iodide ions by an oxidizing agent. The oxidizing agent to be determined reacts with an excess of iodide ions to produce iodine. This liberated iodine is then titrated with a standard solution of a reducing agent, usually sodium thiosulfate. This method is useful for determining oxidizing agents that react too slowly with starch or that cannot be directly titrated with iodine. Examples include the determination of copper(II) ions or oxidizing halogens. Iodometry is widely used in various fields, including environmental analysis, food chemistry, and pharmaceutical quality control.