Unit 3: Section 3 - Alkenes and Alcohols

Question 1

What is an alkene?

Answer 1

Unsaturated hydrocarbons with a C=C double bond

Question 2

What is the general formula of an alkene?

Answer 2

CnH2n

Question 3

Why is there no rotation about the C=C double bond?

Answer 3

Due to the π orbital - electron density above and below the single bond, which holds the carbon atoms in place

Question 4

Are alkenes more or less reactive than alkanes? Why?

Answer 4

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

Question 5

What intermolecular forces of attraction do alkenes have?

Answer 5

Only Van der Waals due to non-polar bonds

Question 6

Are alkenes soluble in water? Why?

Answer 6

No, non-polar bonds (van der Waals’ < hydrogen bonding)

Question 7

Name and describe the 3 kinds of isomers alkenes can have

Answer 7

• Chain isomers (branched chains)
• Position isomers (C=C on different carbon atoms)
• Geometric E-Z isomers (Z is when 2 highest atomic number chains are on the same side of the double bond; E is when they’re on opposite sides)

Question 8

What is the equation for the complete combustion of pent-2-ene?

Answer 8

CH3CH=CHCH2CH3 + 71/2O2 -> 5CO2 + 5H2O

Question 9

What is an electrophile?

Answer 9

Electron deficient atoms/ions which accept a pair of electrons

Question 10

What is the most stable type of carbocation intermediate? Why?

Answer 10

Alkyl groups have a posivite inductive effect, so the most stable carbonation 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 (or the most stable available)

Question 12

What conditions are needed for the electrophilic addition of H2O to an alkene? What is the product?

Answer 12

Acid catalyst, usually phosphoric acid
Alcohol

Question 13

What conditions are needed for the electrophilic addition of a hydrogen halide to an alkene?

Answer 13

Room temperature

Question 14

What conditions are needed for the electrophilic addition of a halogen molecule to an alkene?

Answer 14

Room temperature and organic solvent

Question 15

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

Answer 15

C=C double bond with a high electron density induces a temporary dipole in the halogen molecule -> δ+ atom attracted to double bond

Question 16

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

Answer 16

Add water
H2SO4 reforms, showing it catlayses the hydration of alkenes

Question 17

What is an addition polymer?

Answer 17

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

Question 18

What are monomers? What form do they usually take?

Answer 18

Molecules which combine to form a polymer
Usually have a C=C bond which breaks to leave a repeating pattern

Question 19

Give 3 uses of poly(chloroethene) / PVC?

Answer 19

Drainpipes
Vinyl
Aprons

Question 20

Give 2 examples of plasticisers

Answer 20

Esters
Phthalates

Question 21

What are plasticisers?

Answer 21

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

Question 22

How do the physical properties of PVC change due to a plasticiser? What applications does this lead to?

Answer 22

PVC with a plasticiser become flexible, used for aprons
Without a plasticiser, PVC is rigid, used for drainpipes

Question 23

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

Answer 23

Bonds are non-polar so are not attacked by enzymes

Question 24

Why is a lack of biodegradability in compounds with C-C or C-H bonds a problem?

Answer 24

Disposal is very problematic

Question 25

What is mechanical recycling

Answer 25

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

Question 26

What is mechanical recycling used for?

Answer 26

Soft drinks bottles -> fleeces

Question 27

What is feedback recycling?

Answer 27

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

Question 30

What is a problem with recycling?

Answer 30

Each time thermosoftening plastics are melted and remoulded, their properties degrade, so they can only be remoulded a limited number of times