Iodine value is the number of iodine in gram that is consumed by 100gm of substance under observation.

Iodine numbers are often used to determine the amount of unsaturation in fatty acid.

(unsaturation in form of double bonds, which react with iodine compounds)

Higher the iodine number more C=C bonds are present in the fat.

View full video👇

Methods of Analysis

•Wij’s method:

•place an accurately weighed quantity of the substance under examination in a dry 250ml iodine flask and dissolve it in 10ml of fat solvent(1:1::pet. Ether:ethanol)

•Add 25 ml of ICl solution(Wij’s solution) to it.

•Stopper the flask , shake well and place it in a darkened area for 30min along with blank i.e. flask having all reagent except the oil/fat.

•Add 10ml of 10%KI Solution to the test & blank solution and immediately titrate it against 0.1N sodium thiosulphate until a pale straw colour is observed.

•Than Add about 1ml starch indicator into the flask, a purple colour is observed.Continue the titration until the color of the solution in the flask turns colourless.

Chemical Equations

•iodine monochloride reacts with the unsaturated bonds to produce a di-halogenated single bond.

iodine value

•when reaction is completed , potassium iodide is added to react with remaining ICl which cause molecular iodine to liberate.

iodine value

•The liberated molecular iodine is then titrated with a standard solution of 0..1N sodium thiosulphate.

iodine value

Calculations:

iodine value calculation

•Eq. Wt of iodine=127

•Volume of sodium thiosulphate used =B-A

•B=Volume of sodium thiosulphate used by Blank

•A=Volume of sodium thiosulphate used by Test

•Normality of sodium thiosulphate =0.1N

•Hanus Method:

•Weigh accurately the quantity of the substance under examination as per given table.

iodine value table

•Place sample in 250ml iodine flask which has been rinsed with glacial acetic acid.

•Add 15ml of chloroform and dissolve. Add 25ml iodine monobromide slowly from burette.

•Insert the stopper allow to stand in dark for 30min.

•Shake frequently and add 10ml of 10% KI solution and titrate with 0.1M sodium thiosulphate until a pale straw colour is observed.

•Than Add about 1ml starch indicator into the flask, a purple colour is observed.Continue the titration until the color of the solution in the flask turns colourless.

Note:Calculations are same as in Wij’s method.

•The approximate weight in gm of the substance to be taken may be calculated by dividing highest expected iodine value by 12.7.

•If more than half the available halogens absorbed,test must be repeated with smaller quantity.