Saturation
From ZuluNotes - Free Leaving Cert Notes
In organic chemistry, a saturated compound is one with no double or triple bonds. In saturated hydrocarbons, every carbon atom is attached to two hydrogen atoms, (except those at the ends of the chain). With hydrocarbons, alkanes are saturated, and alkenes and alkynes are unsaturated. The term unsaturated is used when any carbon structure contains double or occasionally triple bonds. Alkynes, with their triple bond, are more reactive in hydrogenation reactions[1]
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Vegetable fats and oils
You may have heard of polyunsaturates in relation to margarine. Unsaturated vegetable fats and oils can be transformed (through hydrogenation) into fats and oils of higher melting point. The hydrogenation process involves "sparging" the oil with hydrogen in the presence of a catalyst, typically nickel. As each double-bond is broken, two hydrogen atoms each form single bonds with the two carbon atoms. The elimination of double-bonds by adding hydrogen atoms is called saturation; as the degree of saturation increases, the oil becomes increasingly like a fat. Margarine is seen as a mid-point between fats (saturated) and oils (unsaturated).[2]
Testing
A substance can be tested for unsaturation by two means: The addition of bromine and addition of acidified KMnO4.
Bromine
If a solution of bromine water is added to an unsaturated compound, the yellow/red colour becomes clear. This colour change is the standard test for testing for the presence of alkenes and alkynes.
Acidified Potassium Permanganate
Acidified Potassium Permanganate can also be used to test for unsaturation. If a very dilute sample is added to an unsaturated substance, the purple colour will turn colourless.
