C1.5 Other useful substances from crude oil

Question 1

What is cracking?

Answer 1

The thermal decomposition (breaking down by heat) of longer hydrocarbons chains into smaller more useful ones

Question 2

Explain the process of cracking.

Answer 2

• The long chain fraction is heated and vapourised
• Vapours pass over a powdered (usually aluminum oxide) catalyst at a temperature of 400 - 700c degrees
• The long chain molecules will split apart on the surface of the catalyst

Question 3

What are the products of cracking?

Answer 3

• Alkenes

- Shorter alkane chains

Question 4

What are alkenes?

Answer 4

Unsaturated hydrocarbons

Question 5

What is the formula for alkenes?

Answer 5

Cn H2n

Question 6

How do alkenes react with bromine water and why?

Answer 6

• They turn it from orange to colourless

- The double C=C bond opens up and bonds with the bromine

Question 7

Why are alkenes unsaturated?

Answer 7

They can make more bonds as the carbon double bond can open up and bond with other atoms

Question 8

What are some products of cracking useful for?

Answer 8

• Fuels e.g petrol for cars and paraffin for jet fuel

- Chemicals for making plastics e.g ethene

Question 9

How is ethanol produced from ethene?

Answer 9

Ethene is hydrated with steam in the presence of a catalyst

ethene + water —-> ethanol

Question 10

What is the advantage of hydrating ethene to make ethanol?

Answer 10

• Cheap
• Few steps
• Not much is wasted

Question 11

What is the disadvantage of hydrating ethene to make ethanol?

Answer 11

Ethene is produced from crude oil which is non-renewable

Question 12

How is ethanol made by fermentation?

Answer 12

• Sugar is converted into ethanol using yeast

sugar ===> carbon dioxide + ethanol

Question 13

What are the advantages of fermentation?

Answer 13

• Lower temperature needed than for hydrating ethene
• Fewer resources needed
• Sugar is renewable
• Sugar can be grown in poor countries

Question 14

What are the disadvantages of fermentation?

Answer 14

• Ethanol from this process isn’t very concentrated and needs to be distilled and purified
• There are more steps involved

Question 15

What is polymerisation?

Answer 15

Joining together small alkene molecules (monomers) to form large alkene molecules (polymers) by opening up their double bonds

Question 16

What are a polymer’s physical properties affected by?

Answer 16

• The temperature of polymerisation

- The pressure of polymerisation

Question 17

What conditions is a flexible, low density poly(ethene) made in?

Answer 17

• 200c degrees

- 2000 atmospheres

Question 18

What conditions is a rigid, dense poly(ethene) made in?

Answer 18

• 60c degrees
• A few atmospheres
• With a catalyst

Question 19

Describe six uses for polymers

Answer 19

• Plastic bags : low density poly(ethene)
• Waterproof coatings for fabrics
• Dental polymers are used in resin tooth fillings
• Hydrogels used for nappies (they absorb water)
• Wound dressing: hydrogels keep wounds moist
• Shape memory polymers : mattresses - they get softer when they get warmer

Question 20

Define ‘biodegradable’

Answer 20

Able to be broken down by microbes

Question 21

What material have some new biodegradable plastics been made from?

Answer 21

Cornstarch

Question 22

What is the disadvantage of recycling polymers?

Answer 22

There are many steps : collection, transportation, washing, separation and melting which uses up energy and therefore fossil fuels and can be expensive

Question 23

What are the disadvantages to using polymers?

Answer 23

• They are products of crude oil, using up crude oil reserves
• This may make them more expensive in the future
• Causes waste and landfill sites