Bromine water is a well-known test for unsaturation in organic compounds. The substances that can decolourise bromine water are primarily alkenes and alkynes, as well as other compounds that contain double or triple bonds.
When these unsaturated compounds are added to bromine water, a chemical reaction occurs where the bromine reacts with the double or triple bonds in the molecules. This reaction results in the formation of a colorless dibromo compound, effectively removing the characteristic orange-brown color of bromine water.
Some common examples of substances that can decolourise bromine water include:
- Ethene (ethylene)
- Propene
- Butyne
- Unsaturated fatty acids
In contrast, saturated compounds, such as alkanes, do not undergo this reaction and therefore do not decolourise bromine water. This property serves as a useful indicator in organic chemistry for identifying the presence of unsaturated compounds.