The Halogenation Test
Shows positive test for:
Unsaturated compounds (triglycerides in this experiment)
How to perform the test:
Five ml of methylene chloride is used to dissolve ~0.1 g of the sample to be tested. If solid material remains, grind it in a mortar and pestle and then filter to remove the solid from the test solution. If a liquid sample is insoluble, take the test solution from the methylene chloride layer. A 5% solution of bromine in methylene chloride (a dark brown solution) is added dropwise to 3 ml of the test solution.
A positive test is indicated by:
a colorless solution. The sample solution remains colorless if an unsaturated compound is present. It turns red/brown if only saturated compounds are present.
a negative test (left) and a positive test (right)
The degree of unsaturation of a compound can be determined by slowly adding bromine solution until the first red/brown color is observed. The more bromine solution required, the greater the unsaturation. In the experiment this is done by counting the drops required.