Iodometry and Iodimetry

Iodometry: The process of determination of any oxidant (element, compound or ion) by the titration of the liberated iodine in the reaction of that oxidant with an iodide salt with standard sodium thiosulphate solution is called iodometry. In this process generally the amount of an oxidizing agent like Cu²⁺, Cr₂O₇^2-, MnO₄^2-  ion is determined. As for example, to determine Cu²⁺  ion, it reacts with KI solution and liberates equivalent amount of iodine.

     2CuSO₄  +  4KI                      =   Cu₂I₂         +   2K₂SO₄    +   3I₂

Then the liberated iodine is determined by titration with standard thiosulphate solution:

     2Na₂S₂O₃  +  I₂                      =   Na₂S₄O₆       +   2NaI

Here, 2 mole Na₂S₂O₃ solution Ξ  1 mole I₂ solution Ξ  2 mole CuSO₄  solution.

Therefore, 1 mole Na₂S₂O₃ solution Ξ  1 mole CuSO₄  solution

Iodimetry: The process of determination of any reductant by the redox titration with standard iodine solution is called iodimetry. In this process, standard iodine solution is used to determine the concentration of reducing agent. For example, during the titration of  sodium thiosulphate solution with standard iodine solution, the reaction occurred is as follows:

     2Na₂S₂O₃  +  I₂         =   Na₂S₄O₆       +   2NaI

Here, 2 mole Na₂S₂O₃  solution Ξ  1 mole I₂  solution,

In iodimetry, a species is directly titrated with an iodine solution, but in iodometry a species is titrated with an iodide solution and then the released iodine is titrated with thiosulphate. Iodometry can be used to quantify oxidizing agents, whereas iodimetry can be used to quantify reducing agents.