Hydrocarbons :Alkenes 4.23-4.28
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4.23 What functional group do alkenes belong to?
Alkenes belong to the -ene functional group Alkenes always have a double bond C = C
4.24 What is the general formula for alkenes?
CnH2n
4.25 Why are alkenes classified as unsaturated hydrocarbons?
They are classified as unsaturated as because alkenes contain double or triple bonds. They can also make more bonds when the double bond opens up
4.27 Describe the reaction of an alkene with bromine:
• Alkene + bromine –> dibromoalkane • This is an addition reaction • This is as the double bond of the alkene opens up, creating a single bond. • The halogen can then be added to one of the carbon atoms. • Turning the bromine water from orange to colourless as all bromine is used up to from dibromoalkane
4.28 How can bromine water be used to to distinguish between an alkane and an alkene?
• When you shake an alkene with orange bromine water, the solution becomes colourless - this is as the bromine molecules, which are orange, are reacting with the alkene to make dibromoalkane, which is colourless. • Alkanes don’t react with bromine water as they don’t have a double bond - so if you add an alkane to bromine water, the solution stays orange.