Iodine atometry

The iodine atometry is a measurement analytical method used for the quantitative determination of oxidizable substances. Iodate salts are used as oxidizing agents for this purpose . The method is related to bromatometry , in which bromate ions are used, and differs from iodometry .

principle

Ideally, the oxidation step of iodine atometry is based on the following reaction , in which iodate ions (IO ₃ ^- ) are reduced to iodide ions :

${\displaystyle \mathrm {IO_{3}^{-}\ +\ 6\ H_{3}O^{+}\ +\ 6\ e^{-}\longrightarrow \ I^{-}\ +\ 9\ H_{2}O} }$

The reduction to iodide is not always quantitative, however, which is why the reaction must be controlled by changing the reaction conditions so that a defined reaction takes place.

One way to do this is by using the Andrews method . According to this protocol, a hydrochloric acid sample solution is used. Under these conditions, added iodate is reduced to elemental iodine according to the following equation :

${\displaystyle \mathrm {2\ IO_{3}^{-}\ +\ 12\ H_{3}O^{+}\ +\ 10\ e^{-}\longrightarrow \ I_{2}\ +\ 18\ H_{2}O} }$

Iodine in turn disproportionate in water according to:

${\displaystyle \mathrm {3\ I_{2}\leftrightharpoons \ I_{3}^{+}\ +\ I_{3}^{-}} }$

Here the existing formal I ⁺ - ions forming with chloride ions , which in the hydrochloric acid solution are provided, iodine monochloride (ICl), which probably with additional chloride ions to the anion [ICl ₂ ] ^- reacting:

${\displaystyle \mathrm {I^{+}\ +\ Cl^{-}\longrightarrow \ ICl\ {\xrightarrow {Cl^{-}}}\ \ [ICl_{2}]^{-}} }$

The titration is carried out in two phases, whereby carbon tetrachloride or chloroform can be used as the organic phase . This changes color during the titration. The titration is finished when the organic phase is completely discolored again.

swell

• G.-O. Müller: Quantitative-inorganic internship . 7th edition, pp. 98-99, Verlag Harri Deutsch, Frankfurt / Main 1992, ISBN 3-8171-1211-4 .