Scribd
Upload
1K views3 pages

Iodometriy

Iodometric titration involves the oxidation and reduction of iodine. There are two types: iodimetry, the direct titration of iodine with a reducing agent, and iodometry, the indirect titration of iodine liberated by an oxidizing agent. Iodimetry is used to determine the concentration of a reducing agent by titrating it with standard iodine solution. Iodometry determines the concentration of an oxidizing agent by having it liberate iodine from potassium iodide, which is then titrated with sodium thiosulfate using starch indicator.

Uploaded by

Sarvesh Gaonkar
Copyright
© © All Rights Reserved
We take content rights seriously. If you suspect this is your content, claim it here.
Available Formats
Download as PDF, TXT or read online on Scribd
1K views3 pages

Iodometriy

Iodometric titration involves the oxidation and reduction of iodine. There are two types: iodimetry, the direct titration of iodine with a reducing agent, and iodometry, the indirect titration of iodine liberated by an oxidizing agent. Iodimetry is used to determine the concentration of a reducing agent by titrating it with standard iodine solution. Iodometry determines the concentration of an oxidizing agent by having it liberate iodine from potassium iodide, which is then titrated with sodium thiosulfate using starch indicator.

Uploaded by

Sarvesh Gaonkar
Copyright
© © All Rights Reserved
We take content rights seriously. If you suspect this is your content, claim it here.
Available Formats
Download as PDF, TXT or read online on Scribd
You are on page 1/ 3

Iodometric Titration

Oxidation and reduction processes involving iodine are called Iodometric


titration.
Iodomertic titration are of two types:
i. Iodimetry (Direct Titration)
ii. Iodometry (Indirect Titration)

Iodimetry

Iodimetry refers to direct iodometric titration with standard solution of


iodine and suitable reducing agent.
The basic principle of iodimety is to determine the concentration of reducing
agent.

Step I: Preparation of Standard iodine solution.

Iodine is less soluble in water; hence iodine solution is prepared by


dissolving iodine in a solution of KI (excess).

Ionic equation:

Step II: The tri-iodide solution is titrated with sodium thiosulphate solution.

Starch is used as indicator.


Iodometry

Iodometry deals with indirect iodometric titration of iodine liberated in


chemical reaction.
The basic principle of iodometry is to determine the concentration of an
oxidizing agent in solution.
In this titration oxidising agent (Cr2O72-,MnO42-,Cu2+, H2O2 ,etc) liberate
iodine from iodide (KI).
The liberated iodine is titrated against standard solution of reducing agent
(Na2S2O3) from burette.

Considering example of dichromate:

Step I: Iodometry involved reaction between the oxidizing agent, (K2Cr2O7) and KI
(excess) thus the iodine is quickly liberated.

Ionic equation:

Step II: The liberated iodine (in step I) is titrated with standard sodium thiosulphate
solution.

Ionic equation:

Starch is used as indicator.


Choice of Indicator

Starch is used as indicator in iodometry titration.


Starch reacts with iodine in the presence of iodide to form an intensly blue-
coloured complex, which is visible at very low concentration of iodine.
The colour sensitivity decreases with increasing temperature of the solution.
The starch is not added at the beginning of the titration when the iodine
concentration is high.
It is added just before the end point when the dilute iodine color becomes
pale yellow.
Because most Iodometry are performed in strongly acid medium and the
starch has a tendency to hydrolyze in acid solution.
Advantage: The great merit of starch is that it is inexpensive.
Disadvantages of starch indicator:
i) Insolubility in cold water.
ii) Instability of suspension in water.
iii) It gives a water-insoluble complex with iodine, the formation of which
precludes the addition of the indicator early in the titration.
Carbon tetrachloride has been used in certain reaction instead of starch
solution.
The reddish-violet colour of iodine in carbon-tetrachloride is visible in very
low concentration of iodine.

You might also like