What is a common test for the presence of an alkene?

The presence of an alkene can be tested using bromine water, which is a common and effective method. When bromine water is added to an alkene, a color change occurs. The reddish-brown color of bromine water will turn colorless as the bromine reacts with the alkene. This reaction occurs because alkenes contain a carbon-carbon double bond that reacts with bromine through an addition reaction, ultimately forming a dibromo product.

This test is specific and reliable for identifying alkenes in organic chemistry. In contrast, adding water, reacting with iodine, or heating with sulfuric acid are not specific tests for the presence of alkenes and do not provide the clear visual indication that the bromine water test does. For example, water may not react or indicate the presence of an alkene as clearly, and iodine or sulfuric acid reactions may involve different types of reactions or products that do not specifically confirm the presence of an alkene. Thus, using bromine water provides a straightforward visual confirmation of an alkene's presence.