Alkenes

Question 1

What are alkenes?

Answer 1

Unsaturated hydrocarbons

Question 2

Why are alkenes more reactive than alkanes? (2)

Answer 2

Because they are unsaturated there is scope to add atoms onto the molecule on either end of the double bond to make it saturated

Because the double bond has a high electron density it makes alkenes susceptible to reactions with molecules which have positive or delta positive charges

Question 3

What are E isomers?

Answer 3

Molecules where the highest priority groups are on opposite sides

Question 4

What are Z isomers?

Answer 4

Molecules where the highest priority groups are on the same side

Question 5

Why do alkenes only have van der waals? (1)

Answer 5

Because they have no polar bond

Question 6

Why are alkenes rarely used as fuels? (1)

Answer 6

Because the double bond between carbon atoms means it is likely incomplete combustion will occur, releasing less energy and more CO(g) or C(s)

Question 7

Why do alkenes undergo electrophilic addition reactions? (1)

Answer 7

Because alkenes are unsaturated so other atoms can be added to saturate the double bond

Question 8

What is a carbocation intermediate? (2)

Answer 8

Ions which have a positive charge on a carbon atom

Only exist for a very short amount of time before reacting further

Question 9

What is the positive inductive effect? (1)

Answer 9

The ability of an alkyl group to release electron density through a covalent bond

Question 10

Why is 2-bromopropane the major product? (3)

Answer 10

Because it is produced via a secondary carbocation.
This is more stable than a primary carbocation
Due to the positive inductive effect

Question 11

What is the test used for presence of alkenes? (2)

Answer 11

Test: bromine water
Observation: decolourises from orange to colourless when added to an alkene

Question 12

What are addition polymers? (1)

Answer 12

A long chain formed from many monomers and no other product is formed

Question 13

Why are plasticisers used in polymers? (1)

Answer 13

Make polymers less rigid so more flexible

Question 14

What is the major problem with plastics? (1)

Answer 14

They are non biodegradable
(non-polar carbon chain so carbon-carbon bonds cannot be hydrolysed)

Question 15

Describe mechanical recycling (4)

Answer 15

Plastics are sorted into their different types
And washed
They are ground into pellets
The pellets are melted down and remoulded into new objects

Question 16

Describe feedstock recycling (3)

Answer 16

Plastics are sorted into their different types
They are heated to a temperature which breaks their polymer bonds
These are then re-polymerised to form new plastics

Question 17

What is the issue with the two recycling methods?

Answer 17

Plastic can only be melted and remoulded a finite number of times before their structural integrity starts to fail, at which point they need to be disposed of

Question 18

What are the uses of polychloroethene?

Answer 18

Aprons
‘Vinyl’ records
Water pipes

Question 19

Why can alkenes be attacked by electrophiles? (2)

Answer 19

The C=C double bond is an area of high electron density
Electrophiles are therefore attracted to the double bond

Question 20

Reagent and condition for electrophilic addition reaction to form hydrogensulfate

Answer 20

H2SO4
High temperature
High pressure