What is the test for unsaturation in alkenes?

The test for unsaturation in alkenes is the bromine water test.

The bromine water test is a simple and effective method to identify the presence of unsaturation, specifically double or triple bonds, in alkenes. Alkenes are hydrocarbons that contain at least one carbon-carbon double bond, which is the site of unsaturation.

In the bromine water test, a few drops of bromine water are added to the alkene. Bromine water is a solution of bromine in water, which has a characteristic orange-brown colour. If the alkene is unsaturated, it will react with the bromine water in a process called addition reaction. The double bond of the alkene breaks, and the bromine atoms add across the carbon atoms that were previously double-bonded. This reaction decolourises the bromine water, turning it from orange-brown to colourless.

The decolourisation of bromine water is a positive test for unsaturation. It indicates that the alkene has at least one carbon-carbon double bond. If the bromine water remains orange-brown, it means that the alkene is saturated, i.e., it does not have any double or triple bonds.

This test is not only useful in identifying alkenes but also in distinguishing them from alkanes, which are saturated hydrocarbons. Alkanes do not react with bromine water under normal conditions, so the solution remains orange-brown.

Remember, safety is paramount when conducting this test. Bromine is a toxic and corrosive substance, so it should be handled with care. Always wear protective clothing, including gloves and safety goggles, when performing the bromine water test.