This is THE classic test for unsaturation — you MUST know this!
What you do:
Add a few drops of bromine water (orange/brown solution) to your sample
Add a few drops of bromine water (orange/brown solution) to your sample
With alkenes:
Bromine water turns colourless (decolourised)
Addition reaction: C=C + Br₂ → C-CBr-CBr (dibromoalkane)
Bromine water turns colourless (decolourised)
Addition reaction: C=C + Br₂ → C-CBr-CBr (dibromoalkane)
With alkanes:
Bromine water stays orange (no reaction)
Alkanes don't have C=C bonds to react with
Bromine water stays orange (no reaction)
Alkanes don't have C=C bonds to react with
Safety: Bromine water is toxic and can cause burns. Always use in a fume cupboard and wear eye protection.
This required practical covers Testing for Alkenes: The Bromine Water Test within Alkenes for GCSE Chemistry. Revise Alkenes in Organic Chemistry for GCSE Chemistry with 20 exam-style questions and 15 flashcards. This is a high-frequency topic, so it is worth revising until the explanation feels precise and repeatable. It is section 5 of 14 in this topic. Revise both the method and the reason for each step, because practical questions often test understanding rather than pure recall.
Practice questions for Alkenes
What is the general formula for alkenes?
Explain what is meant by the term 'unsaturated' when applied to alkenes.
Quick recall flashcards
What are alkenes?
Unsaturated hydrocarbons containing a C=C double bond
How are alkenes produced?
By cracking long-chain alkanes from crude oil