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Iodometry

Iodometry is a quantitative analytical technique used to determine the concentration of oxidizing agents through indirect titration of iodine produced from the reaction of the analyte with iodide ions. The method involves titrating the liberated iodine with sodium thiosulfate, with the endpoint indicated by a starch indicator. While widely used for applications such as chlorine content determination and hydrogen peroxide analysis, iodometry has limitations including sensitivity to light and temperature, interference from reducing agents, and pH sensitivity.

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134 views2 pages

Iodometry

Iodometry is a quantitative analytical technique used to determine the concentration of oxidizing agents through indirect titration of iodine produced from the reaction of the analyte with iodide ions. The method involves titrating the liberated iodine with sodium thiosulfate, with the endpoint indicated by a starch indicator. While widely used for applications such as chlorine content determination and hydrogen peroxide analysis, iodometry has limitations including sensitivity to light and temperature, interference from reducing agents, and pH sensitivity.

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IODOMETRY

Iodometry, also known as iodometric titration, is a quantitative analytical technique used to


determine the concentration of oxidizing agents in a solution. This method involves the
indirect titration of iodine liberated by the reaction between the analyte and an excess of
iodide ions. The endpoint of the titration is typically indicated by a color change facilitated by
a starch indicator.

Principle:

The principle of iodometry is based on redox reactions where an oxidizing agent reacts with
iodide ions (I⁻) to produce iodine (I₂). The liberated iodine is then titrated with a reducing
agent, usually sodium thiosulfate (Na₂S₂O₃), which reduces the iodine back to iodide ions.
The amount of sodium thiosulfate used corresponds to the concentration of the oxidizing
agent in the sample. The reactions involved are:

1. Oxidation Reaction:

Oxidizing agent+2I−→I2

2. Titration Reaction:

I2+2Na2S2O3→2NaI+Na2S4O6

Procedure:

A general procedure for iodometric titration includes the following steps:

1. Preparation of the Sample:


o Dissolve the sample containing the oxidizing agent in a suitable solvent,
typically water.
o Adjust the pH to slightly acidic conditions to facilitate the reaction.
2. Addition of Potassium Iodide (KI):
o Add an excess of KI to the sample solution.
o The oxidizing agent oxidizes iodide ions to liberate iodine, imparting a
brownish-yellow color to the solution.
3. Titration with Sodium Thiosulfate:
o Titrate the liberated iodine with a standardized sodium thiosulfate solution.
o As sodium thiosulfate reduces iodine to iodide, the solution's color fades.
4. Endpoint Detection with Starch Indicator:
o Near the endpoint, add a starch solution as an indicator.
o The starch forms a blue complex with iodine.
o Continue titration until the blue color disappears, indicating the endpoint.
5. Calculation:
o Calculate the concentration of the oxidizing agent based on the volume of
sodium thiosulfate solution used.
Applications:

Iodometry is widely used in various fields for the analysis of oxidizing agents. Some notable
applications include:

 Determination of Chlorine Content: Used to measure the concentration of chlorine


in water treatment facilities and swimming pools.
 Analysis of Hydrogen Peroxide: Employed to determine the concentration of
hydrogen peroxide in disinfectants and bleaching agents.
 Estimation of Copper(II) Ions: Utilized in the quantitative analysis of copper in
metallurgical processes and alloy compositions.

Demerits:

While iodometry is a valuable analytical technique, it has certain limitations:

 Sensitivity to Light and Temperature: Iodine is volatile and can evaporate, leading
to inaccuracies. Exposure to strong light and elevated temperatures can exacerbate
this issue.
 Interference from Reducing Agents: The presence of reducing agents in the sample
can react with the liberated iodine, causing errors in the titration results.
 pH Sensitivity: The reactions involved are pH-dependent. Incorrect pH levels can
lead to incomplete reactions or side reactions, affecting the accuracy of the analysis.

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