Alkenes

Question 1

What type of hydrocarbons are alkenes?

Answer 1

Unsaturated

c double c bonds

Due to the double bonds they have a high electron density making them reactive.

Question 2

What type of mechanism do alkenes undergo?

Answer 2

Addition reactions

Question 3

What attacks alkenes and why?

Answer 3

Electrophiles due to their double bonds which have high electron density

Question 4

What is an electrophile? + eggs

Answer 4

An electrophile is an electron pair acceptor.

-positive charged ions
NO2+

-polar molecules
h-br

Question 5

How to test for alkenes?

Answer 5

Using bromine water

results: colour change from brown/orange to colourless

this world as bromine is the electrophile and adds to the alkene forming a dibromoalkane

Question 6

What do alkenes produce when reacted with hydrogen halide?

Answer 6

Halogenoalkanes (addition reaction)

Question 7

2 different products are produced when reacting hydrogen halides with what?

Answer 7

unsymmetrical alkenes

Question 8

What determines the amount of 2 different products produced?

Answer 8

The amount of 2 products is determined by the stability of the carbocation intermediate.

The more alkyl groups bonded to the carbocation the more stable the intermediate is.

• This is because the alkyl groups push electrons towards the positive carbocation stabilising it. The more stable the carbocation the more likely it will form.

Question 9

Summarise stabilities of carbocations..

Answer 9

1 alkyl group–> least stability (primary carbocation)

2 alkyl group–> middle stability (secondary)

3 alkyl groups–> most stable (tertiary)

products of tertiary carbocation more likely to form.

Question 10

How do you determine the minor and major product?

Answer 10

Minor product– product made at a lower amount due to lower stability

Major product– product made at a high

Question 11

What do alkenes produce when reacted with sulphuric acid? +CONDITIONS

Answer 11

CONDITIONS:
Alkenes react with cold concentrated sulphuric acid

PRODUCE:
intermediate alkyl hydrogen sulfate

CONDITONS:
add cold water to warm ethyl hydrogen sulfate to form ethanol through hydrolysis

PRODUCTS:
Alcohol final product with sulphuric acid reformed as it is a catalyst

Question 12

Alkenes are monomers what can they join to form?

Answer 12

They can join to form addition polymers.

they can be:

1) Natural -> proteins and natural rubber
2) Synthetic-> poly(ethane) and poly(propene)

Question 13

Describe polyalkene properties..

Answer 13

• Most polyalkenes chains are non-polar so they only have van der waals forces between the chains.
• The longer the chain and the closer they are to each other the more van der waals forces you have.
• Polymer chains which are shorter and have a lot of branching tend to be more flexible and weaker.
• Polymers with no or very little branching and long tend to be more rigid and stronger.
• Some polyalkenes have halogens e.g) Chlorine (PVC - common name polyvinyl chloride). They can form stronger permanent dipole-dipole forces and so will different properties to other non-polar.

Question 14

Why are plasticisers used?

Answer 14

To add to polymers to change their properties.

Question 15

What do plasticisers do?

Answer 15

Plasticisers makes polymers more flexible. Plasticisers slide between the polymer chains pushing them apart.

This weakens the intermolecular forces between the chains. The chains can now slide over each other more and makes the polymer easier to bend.

Plasticisers are commonly used to change the properties of PVC - Poly(chloroethene)

PVC is made from long, closely packed polymer chains that are hard but brittle. Used in drain pipes.

Question 16

What happens to PVC when plasticiser is added?

Answer 16

PVC that has plasticiser added is more flexible. It is used for electrical cable insulation and clothing.