Which statement is true about the bromine water test for alkenes?

Which statement is true about the bromine water test for alkenes?

• A. It decolorizes bromine water when a carbon-carbon double bond is present
• B. It only tests for halide ions
• C. It detects carbonyl groups
• D. It tests for aromatic rings

Answer: (A)

The test hinges on detecting unsaturation in a molecule. Bromine water, which contains Br2, reacts with a carbon–carbon double bond through electrophilic addition. The bromine adds across the double bond, forming a dibromo compound and, in the process, the orange-brown color of Br2 is consumed. That loss of color (decolorization) signals that a carbon–carbon double bond is present. This test specifically indicates the presence of alkenes and isn’t a general test for halide ions, carbonyl groups, or aromatic rings. Halide ion tests rely on different reactions (like silver nitrate for halide ions), carbonyl groups are detected with other reagents (such as Tollens or Fehling), and aromatic rings have their own characteristic tests.

The test hinges on detecting unsaturation in a molecule. Bromine water, which contains Br2, reacts with a carbon–carbon double bond through electrophilic addition. The bromine adds across the double bond, forming a dibromo compound and, in the process, the orange-brown color of Br2 is consumed. That loss of color (decolorization) signals that a carbon–carbon double bond is present.

This test specifically indicates the presence of alkenes and isn’t a general test for halide ions, carbonyl groups, or aromatic rings. Halide ion tests rely on different reactions (like silver nitrate for halide ions), carbonyl groups are detected with other reagents (such as Tollens or Fehling), and aromatic rings have their own characteristic tests.