What happens when bromine water is added to an alkane?

• A. The colour changes from brown to colourless.
• B. The colour changes to green.
• C. No colour change is seen.
• D. A precipitate forms.

Answer: (C)

Bromine water tests for unsaturation. Bromine adds across double bonds in alkenes, which makes the orange-brown solution fade to colorless. Alkanes are saturated and have only single bonds, so there’s no double bond for bromine to add to under normal conditions; nothing is consumed and the solution stays brown. Only if you provide UV light to drive radical halogenation would bromine react with an alkane, but without that, no color change is seen.