Alkenes can be identified in the laboratory through a straightforward chemical procedure known as the bromine water test. This test exploits the reaction between alkenes and bromine water, which is a dilute solution of bromine. Alkenes are hydrocarbons characterized by the presence of a carbon-carbon double bond, which is highly reactive and readily breaks to form new bonds with other atoms or molecules.

When bromine water is introduced to an alkene, the bromine reacts with the carbon-carbon double bond. This results in the breaking of the double bond and the attachment of bromine atoms to the carbon atoms. This type of reaction is classified as an addition reaction. As a result of this reaction, the bromine water, which starts off as orange, becomes colourless, indicating a positive test for the presence of an alkene.

To perform the test, a small quantity of the substance being examined is combined with bromine water in a test tube. The test tube is then shaken or stirred to ensure thorough mixing of the substance and the bromine water. If the substance is indeed an alkene, the bromine water will rapidly lose its orange hue and turn colourless. Conversely, if the substance is not an alkene, the bromine water will retain its orange colour.

It is essential to recognize that this test is not exclusive to alkenes. Other compounds, such as alkynes and phenols, can also react with bromine water, leading to a loss of its colour. Therefore, while the bromine water test is useful, it should be complemented with additional tests to accurately confirm the presence of an alkene.