Answer
Decolourisation of Bromine Water
Bromine water is decolourised by compounds that undergo either:
- Electrophilic addition to a C=C double bond, or
- Electrophilic substitution on an activated aromatic ring
Phenol and Aniline:
These compounds have activated aromatic rings (due to –OH or –NH₂ groups), making them reactive toward Br₂ via electrophilic substitution.
➤ Result: Bromine water is decolourised.
These compounds have activated aromatic rings (due to –OH or –NH₂ groups), making them reactive toward Br₂ via electrophilic substitution.
➤ Result: Bromine water is decolourised.
Styrene (vinylbenzene):
Contains a vinyl C=C bond that reacts with Br₂ via electrophilic addition.
➤ Result: Bromine water is decolourised.
Contains a vinyl C=C bond that reacts with Br₂ via electrophilic addition.
➤ Result: Bromine water is decolourised.
Cyclohexane:
A saturated hydrocarbon without unsaturation or aromatic ring activation.
➤ Result: Bromine water is not decolourised.
A saturated hydrocarbon without unsaturation or aromatic ring activation.
➤ Result: Bromine water is not decolourised.
Conclusion: Only compounds with a C=C double bond or an activated aromatic ring can decolourise bromine water through chemical reaction.