Aim: Determination of iodine value of an oil sample

Principal: Iodine value is define as the number of g. of halogen as iodine, that is absorbed by 100 g, of fat/oil. It is a measure of the degree of unsaturation of the sample. The fat oil is treated with an excess of wij’s solution (Iodine monochloride – oxidizing agent). Which contain Iodine monochloride. It reacts with the unsaturated part of the fat/oil. Iodine is than liberated from the unreacted wij’s solution by the reaction with KI. The amount of Iodine is liberated is then determine by titrating with standard Na2S2O3 solution.

Procedure: weight out accurately between 0.4 to 0.8 g. of fat/oil, in a conical flask. Dissolve the fat in 10 ml CCl4 and add 25 ml of wij’s solution. Simultaneously prepare a blank sample as above without the oil sample, mix well and allow the samples to stand in the dark. For about 30 min. at the end of this time add to each flask 20 ml 15% KI solution and 100 ml distilled water. Titrate the liberated Iodine with 0.1 N Na2S2O3 solution to a pale yellow color add then 2 to 3 ml starch solution and titrate  with Na2S2O3 solution till the solution is colorless.

Result: The Iodine value of given fat/oil sample is; ______

Calculation:

Calculation the Iodine value of the fat/oil given that the difference between the volume of Na2S2O3 solution used in the blank and in the test sample gives the amount equivalent to the Iodine absorbed by the fat/oil.

  • Weigh of fat/oil taken: ___________
  • Blank reading of Na2S2O3 (B): _________
  • Test solution reading of Na2S2O3 (T): _________
  • Iodine value of = \frac{(B - T)\times N\times 126.9 \times 100}{1000\times W}

T = ml of the Na2S2O3 solution required for oil sample

B = ml of Na2S2O3 solution required during blank titration

N= normality of Na2S2O3 solution

W= weight of an oil sample in g.