Determination of Iodine Value of Fatty Acid by Extraction and Titration

The iodine value of a substance is defined as the weight of iodine absorbed by 100 parts by weight of the substance. The method determines the Iodine Value for soap and soap noodles.

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Separating flask



Methyl Orange Solution (0.05% w/v).

Ethyl ether.

Sodium Chloride Solution-saturated.


Sulphuric acid.

Carbon Tetra-Chloride, A.R grade.

Wij's Iodine Monochloride Solution Preparation 

Dissolve 10 ml of Iodine Monochloride in about 800 ml of Glacial Acetic Acid and shake vigorously. 

Store in a glass stoppered bottle in a cool place, protected from light. 

Pipette 5 ml of this, add 10 ml Potassium Iodide solution (10% w/v), and titrate with 0.1 (N) Sodium Thiosulphate solution using starch solution as indicator. 

Adjust the volume of this solution till it is 0.2 (N) Starch solution.

10% w/v Potassium Iodide solution.

Sodium Thiosulphate, 0.1(N).

Iodine Value of Fatty Acid by Extraction

The Procedure of Iodine Value

Fatty acid extraction from soap and soap noodles

4.1 Dissolve 5 gm of the grated sample in 100 ml of distilled water by warming it in a 250 ml conical flask in a water bath.

4.2 Add 2 to 3 drops of methyl orange solution (0.05% w/v in alcohol)

4.3 Add dilute Sulphuric Acid (1:1) till the color changes to pink.

4.4 Insert a small funnel into the neck of the flask, and heat the flask to a temperature not exceeding 60 °C until the fatty acids separate as a clear layer.

4.5 Add 50 ml of saturated sodium chloride solution and cool.

4.6 Transfer the contents to a separating funnel, draw off the aqueous acid layer into a second separating funnel, and shake it with three 50 ml portions of ethyl ether.

4.7 Dissolve the fatty acids in the ether used for washing the aqueous liquid and extract with 10 ml portions of water until the extracts are no longer acidic to methyl orange indicator.

4.8 Take out an ether layer in a beaker containing anhydrous sodium sulfate.

4.9 Filter it through a No. 1 Whatman filter paper into a tared beaker.

4.10 Distil off the ether slowly on a steam bath, and to the residue, add 5 ml of acetone.

4.11 Warm the beaker in the steam bath at about 90 °C for 10 minutes. Allow to cool the baker and weigh.

4.12 Return the flask to the water bath for another 10 minutes, allow to cool, and reweigh.

4.13 Repeat the process until the difference between two consecutive weights is less than 0.005 g.

4.14 Transfer about 0.3 gm (W, accurately weighed) of the fatty acids obtained in case of total fatty matter content determination in a dry 250 ml Iodine flask.

4.15 Dissolve in 25 ml Carbon Tetrachloride, warming if necessary to effect solution.

4.16 Transfer 25 ml of Carbon tetrachloride to a second dry 250 ml Iodine flask.

4.17 Pipette 25 ml of Wij's Iodine monochloride solution into each flask, insert the stoppers, previously moistened with Potassium Iodide solution (10% w/v KI), swirl for intimate mixing and allow to stand in a dark place for 30 minutes at 15 to 25 °C.

4.18 Place 15 ml of Potassium Iodide solution in the cup tops, carefully remove the stoppers, and rinse the stoppers and the sides of the flask with 100 ml of water in each case.

4.19 Shake and titrate the contents of each flask with 0.1(N) Sodium Thiosulphate, using starch mucilage added towards the end of the titration, as an indicator.


                                                            1.269 x (V1 - V2)

Iodine value of the fatty matter = ---------------------


V1= Volume of 0.1(N) Sodium thiosulphate required for Blank in ml.

V2= Volume of 0.1(N) Sodium thiosulphate required for Sample in ml.

W = Weight of the sample taken in gm.

Potassium Antimonate Solution Preparation Procedure 


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