Bromine water

A bottle of bromine water showing corrosive hazard

This is an aqueous solution of liquid bromine. It is corrosive and gives off a harmful vapour, so should be handled with care. It is usually used to test for unsaturation. If an alkene is shaken with bromine water there is a colour change from orange to colourless. This reaction occurs readily at room temperature. It is an addition reaction in which the bromine adds across the double bond to form a 1,2-dibromoalkane. For example, with the cyclohexene used in the video 1,2-dibromocyclohexane is formed:

Video - testing for alkenes, the reaction of bromine water and cyclohexene