Bromine Water Experiment

Identify data, plan and perform a first-hand investigation to compare the reactivities of appropriate alkenes with the corresponding alkanes in bromine water



  • Bromine water has a distinctive brown colour.
  • Saturated: Containing only single carbon-to-carbon bonds.
  • Unsaturated: Containing at least one double carbon-to-carbon bond.
  • Alkenes react spontaneously with bromine water due to their unsaturated nature.
    • The reaction between an alkene and bromine involves the breaking open of the alkene’s double bond and the inclusion of bromine in its structure (an addition reaction).
    • This results in the production of an alkane with two bromine functional groups.
    • Therefore, when alkenes come into contact with bromine water, they cause it to decolourise.
  • Alkanes do not react with spontaneously bromine water due to their saturated nature.
    • Bromine is non-polar and therefore dissolves more readily in a non-polar alkane than in polar water.
    • Therefore, when alkanes come into contact with bromine water, they cause it to decolourise, while they adopt the colour.
    • If placed in ultraviolet light, a substitution reaction may occur between an alkane and bromine water.
    • This results in the production of hydrogen bromide and an alkane with a single bromine functional group.
    • Therefore, when alkanes come into contact with bromine water and are exposed to ultraviolet light, both substances decolourise.
  • Cyclohexane and cyclohexene can be used to demonstrate these reactions.

Reaction of cyclohexene and bromine water




Structure of cyclohexene

Easychem - Bromine Water Experiment


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