What is the test for alkenes using bromine water?

The test for alkenes using bromine water involves adding bromine water to a substance and observing a colour change.

In more detail, the bromine water test is a simple chemical test used to determine whether a substance contains an alkene functional group. Alkenes are a type of hydrocarbon that contain a carbon-carbon double bond. This double bond is what makes alkenes reactive and allows them to undergo addition reactions, such as the reaction with bromine water.

To perform the test, you would add bromine water, which is a yellow-orange solution, to the substance you are testing. If the substance contains an alkene, the bromine will react with it and the solution will decolourise, turning from yellow-orange to colourless. This is because the bromine is added across the double bond, forming a colourless dibromo compound.

If the bromine water remains yellow-orange, this indicates that the substance does not contain an alkene. This is because substances that do not contain a carbon-carbon double bond, such as alkanes, do not react with bromine water in the same way.

It's important to remember that while this test can indicate the presence of an alkene, it is not definitive proof. Other substances can also decolourise bromine water, so further tests may be needed to confirm the presence of an alkene. However, for GCSE level chemistry, the bromine water test is a useful and straightforward way to identify potential alkenes.