Determination of Iodine Value With Wij's Solution

Determination of iodine value in Oils, Fats, and Wax by Wij's Solution method. This method applies to all types of oils and wax. 

 APPARATUS

a). Glass stoppered Iodine flasks, 500ml.

b). Glass stoppered Volumetric flasks.

c). Pipette, 20ml.

d). Two Pipettes, 25ml.

e). Filter Paper, Whatman No.41H, or equivalent.

REAGENTS FOR IODINE VALUE

a). Wij’s Solution, Reagent Grade.

b). Carbon tetrachloride (CCl4) or Chloroform (CHCl3)

c). Potassium Iodide (KI), reagent grade.

d). 0.1N Sodium thiosulphate(Na2S2O3.5H2O)

e). Starch Solution as an Indicator.

The Procedure of Iodine Value 

In this method, Wij’s reagent is first prepared by dissolving 8.5gms of iodine and 7.5gms of iodine monochloride in warm glacial acetic acid and then making up to 1000cc, in cold water.

a). Weigh accurately 0.1gm (if unsaturation is high) to 0.5gm (if unsaturation is low) of the sample in a 250ml glass stoppered flask.

b). Dissolve the sample in 10ml of chloroform(CHCl3) or carbon tetrachloride(CCl4) warming slightly if necessary.

c). Cool the solution well if warmed, and then again add a similar volume of 10ml of chloroform(CHCl3) or carbon tetrachloride(CCl4) to another flask containing no sample(Blank).

d). Now add 25ml of Wij’s solution into the flask containing the sample and an equal volume (25ml)into the blank.

e). Shake each flask vigorously and allow it to stand in the dark for half an hour. Now the solutions in each flask are diluted with 50-100ml of water and 15cc of 10% KI solution is added to the solution in each flask.

f). The stopper and sides of the beaker are rinsed with water.

g). Now titrate the solutions, with standard 0.1N Sodium Thiosulphate solution (Standardized with standard K2Cr2O7 solution).

h). Starch solution is added when the yellow colour nearly disappears with the addition of the sulfate.

i). Titrate the solution up to the endpoint, when the blue colour formed by the addition of starch is suddenly discharged.

CALCULATION

Iodine value formula

\[Iodine Value (IV) = (B - S) * N * 12.692 / (Weight)\]

                                   

Where

B=ml of thiosulphate required by blank

S= ml of thiosulphate required by the sample

N=Normality of thiosulphate

What is called iodine value?

The iodine value is a measure of the unsaturation or amount of unsaturated fatty acids present in fats and oils. It is expressed as the number of grams of iodine that react with 100 gm of the sample.