CH14 Alkenes

Question 1

What is an alkene

Answer 1

Unsaturated hydrocarbons with a C=C double bond

Question 2

What is an alkene

Answer 2

Unsaturated hydrocarbons with a C=C double bond

Question 3

General formula

Answer 3

CnH2n

Question 4

Why is there no rotation about the C=C

Answer 4

Due to the pi orbital - electron density above and below the single bond holding C atoms in place

Question 5

Are they more or less reactive than alkanes - why

Answer 5

More reactive - high electron density of double bond and pi-bond is slightly easier to break

Question 6

What intermolecular forces of attraction do they have

Answer 6

Only van der Waals due to non-polar bonds

Question 7

Are they soluble in water - why

Answer 7

Non, non-polar bonds

Question 8

Name and describe 3 kinds of isomerism

Answer 8

Chain isomers (branched chains)
Position isomers (C=C on different C atoms)
Geometric E-Z isomers (Z - 2 highest atomic number chains are on the same side. E - they are on opposite sides)

Question 9

What is an electrophile

Answer 9

Electron deficient atoms/ions which accept a pair of electrons

Question 10

Most stable kind of carbocation intermediate - why

Answer 10

Alkyl groups have a positive inductive effect - the most stable carbocation is the one bonded to the most other carbon atoms

Question 11

Major products will be formed from which kinds of carbocations

Answer 11

Tertiary (most stable available)

Question 12

Conditions needed for the electrophilic addition of H2O to an alkene

Answer 12

Acid catalyst (phosphoric acid)

Question 13

Products for this reaction

Answer 13

Alcohol

Question 14

Conditions needed for the electrophilic addition of a hydrogen halide to an alkene

Answer 14

Room temperature

Question 15

Conditions needed for the electrophilic addition of a halogen molecule to an alkane

Answer 15

Room temperature and organic solvent

Question 16

How does a molecule with a non-polar bond react as if it is an electrophile

Answer 16

C=C with a high electron density induces a temporary dipole on the halogen molecule

Question 17

How would you turn sulfuric acid and ethene into an alcohol - how does this show that sulfuric acid catalyses the addition of water to an alkene

Answer 17

Add water

H2SO4 reforms, showing it catalyses the hydration of alkenes

Question 18

What is an addition polymer

Answer 18

Many monomers bonded together via rearrangement of bonds without the loss of any atom or molecule

Question 19

What are monomers - what form do they usually take

Answer 19

Molecules which combine to form a polymer

Usually have a C=C bond which breaks to leave a repeating pattern

Question 20

3 uses of poly(chloroethene)/PVC

Answer 20

Drainpipes
Vinyl
Aprons

Question 21

2 examples of plasticisers

Answer 21

esters

phthalates

Question 22

What are plasticisers

Answer 22

Small molecules that get between polymer chains to force them apart and allow them to slide over one another

Question 23

How do physical properties of PVC change due to a plasticisers

Answer 23

PVC with a plasticiser becomes flexible, used for aprons

Without a plasticiser, PVC is rigid and used for drainpipes

Question 24

Why do things containing mainly C-C and C-H bonds not decompose easily

Answer 24

Bonds are non-polar so are not attacked by enzymes

Question 25

Why is a lack of biodegradability a problem

Answer 25

Disposal is very problematic

Question 26

What is mechanical recycling

Answer 26

Where plastics are separated into different types, washed, ground down, melted and re-moulded

Question 27

What is mechanical recycling used for

Answer 27

Soft drinks bottles –> fleeces

Question 28

What is feedstock recycling

Answer 28

Plastics heated to a temperature which break polymer bonds, leaving original monomers that can be made into new plastics

Question 29

What is feedstock recycling used for

Answer 29

Making totally new plastics