Specification Point 4.27:
Describe the reactions of Alkenes with Bromine to produce Dibromoalkanes
Reactions of Alkenes with Bromine
Alkenes: A homologous series of hydrocarbon compounds with double carbon bonds that has the general formula CnH2n.
Reaction between Alkenes and Bromine:
The reaction between bromine and alkenes is an example of a type of reaction called an addition reaction. This reaction is an addition reaction as the diatomic bromine atom has been added across the double bond of the ethene.
Example: Addition reaction of ethene and bromine
Ethene + Bromine → Dibromoethane
C2H4 Br2 C2H4Br2
Specification Point 4.28:
Describe how Bromine water can be used to distinguish between an Alkane and an Alkene
Alkanes: A homologous series of hydrocarbon compounds with only single carbon bonds that has the general formula CnH2n+2
Alkenes: A homologous series of hydrocarbon compounds with double carbon bonds that has the general formula CnH2n
Use of Bromine Water to distinguish between Alkane & Alkene
The presence of the C=C double bond allows alkenes to react in ways that alkanes cannot. This allows us to tell alkenes apart from alkanes using a simple chemical test:
The result of the test using bromine water with alkanes and alkenes
- Bromine water is an orange solution of bromine.
- When bromine water is shaken with an Alkane, it will remain as an orange solution as alkanes do not have double carbon bonds (C=C).
- But when bromine water is shaken with an alkene, the alkene will decolourise the bromine water and turn colourless as alkenes do have double carbon bonds (C=C).
- This reaction between alkenes and bromine is called an addition reaction.
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