Iodometry, also known as iodometric titration, is a volumetric chemical analysis method based on a redox titration in which the presence or disappearance of elementary iodine is used to determine the endpoint of the titration. It is a type of titration in which the Iodide solution is titrated with an oxidizing agent. The oxidation of iodide to iodine is the basis of iodometry.
End point of iodometric titration:
A starch solution is used as an indicator in an iodometric titration as it can absorb the I2 that is released. This absorption causes the color to change from deep blue to pale yellow when the solution is titrated with a standardized thiosulfate solution. This indicates the endpoint of the iodometric titration.
It is a technique for determining the amount of oxidizing chemicals in a solution. The concentration of the oxidizing agent is measured by titration of iodine with thiosulfate in which starch is used as an indicator. The detection of the endpoint is based on the formation of the blue starch complex.
The following is the chemical reaction:
I2+Na2S2O3→2NaI+Na2S2O4
The reduction of iodine shows by this principle.
Due to thiosulphate decomposition, iodometric titrations are performed in a weak-acidic medium. Because iodine disproportionates at basic pH, iodimetric titrations are carried out in neutral or moderately alkaline (pH 8.0) or weakly acidic solutions.
Frequently Asked Question (FAQ):
Why the endpoint in iodometric titration is colorless?
Starch is a branched molecule in which iodine (I2) is trapped; therefore, gives it a blue color. However, at the end of the titration, when all of the iodine (I2) has transformed into iodide (I-) ions (after the thiosulphate ion has reduced it), there is no more iodine (I2) to be trapped in starch, so the blue color fades.
Is starch solution an indicator?
To detect the presence of iodine, a starch solution is commonly used as an indicator. A deep-blue starch–iodine complex is formed when starch and iodine are present together.
Why iodometric titrations are done in dark?
Because light accelerates a side reaction in which atmospheric oxygen oxidizes iodide ions to iodine, the reaction mixture should be kept in the dark before titration.
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