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Alkenes
AQA A Level Chemistry
| Question | Answer |
|---|---|
| What is an alkene? | A hydrocarbon with a carbon-carbon double bond |
| Why are alkenes described as unsaturated? | They have a carbon-carbon double bond |
| Describe the electron density of the double bond | It is a region of high electron density |
| Draw the shape of the carbon-carbon double bond orbitals | Draw |
| What type of isomerism can alkenes exhibit? | Stereoisomerism (E-Z or cis-trans) |
| What physical feature of alkenes causes their stereoisomerism? | That the double bond cannot rotate |
| What two type of reactions do alkenes typically undergo? | Electrophilic addition or polymerisation |
| Which three reagents do alkenes typically react with? | HBr, H₂SO₄ and Br₂ |
| What type of reagents do alkenes react with? | Electrophiles |
| What are the products of an electrophilic addition reaction with Br₂? | A dibromoalkane |
| Draw a reaction mechanism for a given alkene with Br₂ | Draw |
| Why is bromine water used as a test for alkenes? | The Br₂ reacts with the alkene so its reddish-brown colour is decolourised |
| What are the products of an addition reaction with HBr? | A bromoalkane |
| What is a carbocation intermediate? | An intermediate molecule in a reaction which has a positive charge on a carbon atom |
| Describe the variation in stabilities of the different orders of carbocation | Tertiary > secondary > primary |
| How does stability of carbocations effect the products of an addition reaction with HBr? | More stable carbocation is formed resulting in a major and minor product |
| Draw a mechanism for an addition reaction of an alkene and HBr. Draw and label the major and minor products. | Draw |
| What is the product of a reaction with an alkene and concentrated H₂SO₄? | An alcohol |
| Draw a mechanism for the reaction between a given alkene and concentrated sulphuric acid | Draw |
| Why can sulphuric acid be considered a catalyst in hydration of alkenes? | It is regenerated by the end of the reaction. |
| What are addition polymers formed from? | Alkenes and substituted alkenes |
| How are addition polymers named? | Poly(name of original alkene) |
| What are the chemical properties of addition polymers? | Generally unreactive |
| Why are addition polymers unreactive? | Strong C-C and C-H bonds |
| What is PVC? | Poly(chloroethene) |
| What is a plasticiser? | A small molecule that can get inbetween polymer chains resulting in them being able to slide over one another more easily |
Created by:
JBearfield
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