AQA GCSE Science A

C 1.5 Useful substances from oil

Name: ..Date: .

C1.5 Other useful substances from crude oil Fractions from the distillation of crude oil can be broken down (cracked) to make smaller molecules including unsaturated hydrocarbons such as ethene. Unsaturated hydrocarbons can be used to make polymers and ethene can be used to make ethanol. Ethanol can also be made by fermentation. Key words

Hydrocarbons

Cracked

Molecules

Vapours

Catalyst

Thermal decomposition

Alkanes

Alkenes

Double bond

Cracking

Polymers

Monomers

Biodegradable

Microbes

Hydration

Catalyst

Fermentation

Chemicals

Ethene

Propene

Bromine water

Poly(ethane)

Poly(propene)

C1.5.1 Obtaining useful substances from crude oil a) Hydrocarbons can be cracked to produce smaller, more useful molecules. This process involves heating the hydrocarbons to vaporise them. The vapours are either passed over a hot catalyst or mixed with steam and heated to a very high temperature so that thermal decomposition reactions then occur. b) The products of cracking include alkanes and unsaturated hydrocarbons called alkenes. Alkenes have the general formula CnH2n c) Unsaturated hydrocarbon molecules can be represented in the following forms:

The = represents a double bond. d) Alkenes react with bromine water, turning it from orange to colourless.

e) Some of the products of cracking are useful as fuels.

The longer chain hydrocarbons are not as useful as fuels because they dont ignite easily. However, they can be broken down into shorter chain hydrocarbons which are more useful. This process is called cracking.

Cracking involves heating the hydrocarbons and passing the vapours produced over a hot catalyst.

Some of the products of cracking are used as fuels, but others are used to make plastics.

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C1.5.2 Polymers a) Alkenes can be used to make polymers such as poly(ethene) and poly(propene). In these reactions, many small molecules (monomers) join together to form very large molecules (polymers). For example: Candidates should be able to recognise the molecules involved in these reactions in the forms shown in the subject content. They should be able to represent the formation of a polymer from a given alkene monomer. b) Polymers have many useful applications and new uses are being developed, for example:

new packaging materials,

waterproof coatings for fabrics,

dental polymers, wound dressings,

hydrogels,

smart materials (including shape memory polymers). Candidates should consider the ways in which new materials are being developed and used, but will not need to recall the names of specific examples. c) Many polymers are not biodegradable, so they are not broken down by microbes and this can lead to problems with waste disposal. Knowledge of specific named examples is not required, but candidates should be aware of the problems that are caused by landfill sites and by litter. d) Plastic bags are being made from polymers and cornstarch so that they break down more easily. Biodegradable plastics made from cornstarch have been developed.

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C1.5.3 Ethanol a) Ethanol can be produced by hydration of ethene with steam in the presence of a catalyst.

ethene + steam ethanol

C2H4 + H2O C2H5OH

An ethanol plant.

b) Ethanol can also be produced by fermentation with yeast, using renewable resources. This can be represented by:

sugar carbon dioxide + ethanol

C6H12O6 2CO2 + 2C2H5OH Using ethane to make ethanol needs non-renewable crude oil as its raw material, whereas fermentation uses renewable plant material.

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GCSE Exam questions

Q1. The equation below shows the cracking of a hydrocarbon compound into two different compounds, A and B.

(a) State two differences between the structures of compounds A and B.

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(b) Why is compound A useful in industry?

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Q2. The diagram shows an apparatus that can be used to carry out cracking reactions in a laboratory.

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(a) Why is aluminium oxide or broken porcelain used?

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(b) Paraffin contains decane. The cracking of decane can be represented by the equation below. A decane molecule is split into two smaller molecules.

Complete the equation by adding the formula of the other product.

C10H22 (l) .................... (l) + C2H4 (g) decane

(1)

(c) Would you expect C2H4 molecules to collect at position A or B shown on the diagram?

Position ............................

Explain your answer.

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(d) Cracking reactions involve thermal decomposition.

What is meant by thermal decomposition?

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(e) Explain, as fully as you can, why cracking is used in the oil industry.

To gain full marks in this question you should write your ideas in good English. Put them into a sensible order and use the correct scientific words.

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(f) The cracking reaction produces a mixture of products. The mixture contains hydrocarbons with different boiling points.

Suggest a method of separating this mixture.

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(Total 9 marks)

Q3 Modem window frames are often made from uPVC which contains the plastic poly(chloroethene).

Replace your old wooden windows with our super high quality uPVC

windows!

(a) State why plastic window frames need no painting or maintenance.

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(b) Poly(chloroethene) is a polymer formed by the addition polymerisation of chloroethene.

(i) Chloroethene is an unsaturated molecule. Why is this molecule said to be unsaturated?

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(ii) Complete the diagram to represent how poly(chloroethene) is formed from chloroethene.

(3)

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(iii) Explain what is meant by the term polymerisation.

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(iv) Why is this an addition polymerisation?

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(Total 8 marks)

Q4. Known crude oil reserves are being used up rapidly. Crude oil is used to produce many useful fuels, such as petrol. One way to conserve crude oil reserves would be to increase the production of bio-fuels.

(a) Ethanol can be produced for use as a bio-fuel. Cars can be powered by ethanol or ethanolpetrol mixtures.

Sugar cane can be fermented to give a mixture of water (boiling point 100 C) and ethanol (boiling point 78 C).

(i) How can ethanol be separated from water?

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(ii) Ethanol, C2H5OH, burns to release heat energy.

Complete the balanced symbol equation by writing in the formulae of the two products.

C2H5OH + 3O2 2......... + 3......... (2)

(b) The cost of producing a bio-fuel, such as ethanol, by fermentation, is at least three times higher than the production cost of petrol. It costs less to produce ethanol from alkanes. In the production, the vapour of an alkane is passed over a hot catalyst.

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Ethene is then converted into ethanol.

(i) What has happened to the hexane to produce ethene?

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(ii) Complete the structural formula for ethene, C2H4.

C C (1)

(iii) Name the compound that is added to ethene to produce ethanol, C2H5OH.

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(c) As explained in parts (a) and (b), ethanol can be made using either sugar or alkanes as the starting material.

Evaluate the advantages and disadvantages of using these two starting materials to produce ethanol.

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(Total 10 marks)

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Q5. Polymers are used to make many materials that people need.

(a) Plastic bags are used to carry, protect and store food. Plastic bags are made from polymers.

(i) Ethene is the small molecule (the monomer) used to make the polymer for this plastic bag.

Name the polymer that is made from ethene.

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(ii) Use the correct word from the box to complete the sentence about ethene.

condensing corroding cracking

Ethene is made by breaking down large hydrocarbon molecules into smaller

hydrocarbon molecules by a process called ..................................................... (1)

(iii) The hydrocarbon ethene has the formula C2H4

Complete the sentence about ethene.

Ethene is a hydrocarbon made up of carbon and .......................................... atoms. (1)

(b) The hydrocarbons used to make ethene come from crude oil. The properties of hydrocarbons are linked to the number of carbon atoms in their molecules.

Number of carbon atoms 5 6 7 8 9

Boiling point in C 36 69 99 125 151

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(i) Use the data in the table to complete the bar chart.

(2)

(ii) What happens to the boiling point of a hydrocarbon as the number of carbon atoms increases?

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(iii) All the hydrocarbons in the table are found in petrol. Petrol is one of the fractions separated from crude oil.

Describe how the fractions are separated from crude oil.

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(c) Most plastic bags that are made of hydrocarbons are not biodegradable.

Used plastic bags can be:

dumped into large holes, which is called landfill

burned to give out heat energy, which would produce large amounts of gases.

Would burning used plastic bags be better for the environment than dumping them in landfill?

Explain your answer.

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Q6. Tablet containers are often made from two different polymers.

(a) Ethene, C2H4, and propene, C3H6, can be made from crude oil.

(i) Complete the following sentence.

Ethene and propene are called hydrocarbons because they are made up of carbon

and ..................................................... atoms only. (1)

(ii) Ethene molecules are used to form poly(ethene) molecules.

Complete the diagram to show the poly(ethene) molecule.

Ethene molecules Poly(ethene) molecule

(2)

(b) The tablet containers could be disposed of in a landfill site or could be recycled.

(i) Suggest two reasons why disposing of the tablet containers in a landfill site could cause problems.

1 .......................................................................................................................

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2 .......................................................................................................................

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(ii) Suggest one reason why recycling the tablet containers would be difficult.

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Q7. The hydrocarbons in crude oil can be separated into useful fractions.

Fraction Boiling point

in C

Carbon chain length

Relative % in crude oil

Relative % demand

Naphtha 20180 59 10 20

Gasoline (petrol) 20200 510 10 20

Kerosene (paraffin) 180260 1016 15 23

Diesel 260340 1420 20 25

Fuel oil 370600 2070 45 12

(a) Why does gasoline (petrol) have a lower boiling point than fuel oil?

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(b) Suggest why gasoline (petrol) costs more than fuel oil.

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(c) Describe how fuel oil can be changed into gasoline (petrol).

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Q8. Plastics are used to make many everyday items, such as the body of the kettle.

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(a) Complete the sentences by drawing a ring around the correct words.

(i) The plastic is made from many small molecules called

catalysts

monomers

polymers

(1)

(ii) Propene is produced by cracking some of the fractions that are

separated from

crude oil

limestone

metal ores

(1)

(b) After a few years the kettle no longer worked.

Some parts of the kettle are made of plastic. Some parts of the kettle are made of stainless steel. The owner of the kettle disposed of it in a landfill site.

Consider these statements.

Suggest three reasons why the kettle should not be disposed of in a landfill site.

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(Total 5 marks)

Q9. (a) PEX is a material that is used as an alternative to copper for hot water pipes.

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PEX is made from poly(ethene).

(i) Describe how ethene forms poly(ethene).

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(ii) PEX is a shape memory polymer. What property does a shape memory polymer have?

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(iii) The simplified structures of poly(ethene) and PEX are shown.

Poly(ethene) PEX

Poly(ethene) is a thermoplastic that softens easily when heated.

Suggest and explain how the structure of PEX changes this property.

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(b) Copper was considered to be the most suitable material to use for hot water pipes.

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PEX is now used as an alternative material for hot water pipes.

Copper is extracted from its ore by a series of processes. 1 The low-grade ore is powdered and concentrated. 2 Smelting is carried out in an oxygen flash furnace. This furnace is heated to

1100 C using a hydrocarbon fuel. The copper ore is blown into the furnace with air, producing impure, molten copper.

3 Oxygen is blown into the impure, molten copper to remove any sulfur. The copper is cast into rectangular slabs.

4 The final purification of copper is done by electrolysis.

PEX is made from crude oil by a series of processes. 1 Fractional distillation 2 Cracking 3 Polymerisation 4 Conversion of poly(ethene) into PEX

Suggest the possible environmental advantages of using PEX instead of copper for hot water pipes.

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Q10. Crude oil is used to make useful substances such as alkenes and plastics.

(a) The alkene shown is ethene.

(i) Tick ( ) the correct formula for ethene.

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Formula ( )

CH4

C2H4

C2H6

(1)

(ii) Tick ( ) the name of the plastic formed when many ethene molecules join together.

Name of plastic ( )

Poly(ethene)

Poly(ethanol)

Poly(propene)

(b) Read the article about plastics and then answer the questions.

THE PROBLEM WITH PLASTIC WASTE

The UK produces about 3 million tonnes of plastics from crude oil every year.

Most of the litter found on UK beaches is plastic waste.

80% of the plastics produced end up in landfill sites.

The UK recycles only 7% of plastic waste.

(i) Draw a ring around the correct answer in the box to complete the sentence.

Litter that is plastic waste needs to be removed from beaches

because it

decomposes

is flammable

is not biodegradable

.

(ii) Suggest a problem caused by 80% of the plastics going to landfill sites.

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(iii) The UK government has set a target to recycle 30% of plastic waste.

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How are resources saved by recycling more plastics?

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(Total 5 marks)

Q111. Crude oil is a resource from which fuels can be separated.

(a) The name of the main fuel fractions and one of the hydrocarbons in each fraction are shown in the table.

(i) How does the number of carbon atoms in a hydrocarbon affect its boiling point?

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(ii) Suggest the lowest temperature to which crude oil needs to be heated to vaporize all the hydrocarbons in the table.

Temperature = ................................................ C (1)

(iii) Dodecane boils at 216 C. At what temperature will dodecane gas condense to liquid?

Temperature = ................................................ C (1)

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(b) The bar chart shows the relative supply and demand for the petrol and diesel fractions.

(i) How does the relative supply and demand for petrol and diesel fractions cause problems for an oil company?

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(ii) Suggest one way an oil company could solve these problems.

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(Total 6 marks)

Q12. Water sold in plastic bottles has a high carbon cost.

The carbon cost depends on the amount of carbon dioxide emitted in making and transporting the product.

The more carbon dioxide emitted, the higher the carbon cost.

(a) Plastic water bottles are made from a polymer. The polymer is made from ethene. Ethene is made by cracking hydrocarbons.

(i) Name the polymer made from ethene.

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(ii) Ethene can be made by cracking the hydrocarbon pentane, C5H12.

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C5H12 C2H4 + C3H8

Explain why there is a carbon cost for the process of cracking a hydrocarbon.

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(b) The diagram shows information about water sold in plastic bottles in the UK. The diagram also shows the average distances that water and plastic bottles are transported.

Suggest how the high carbon cost of water sold in plastic bottles could be reduced.

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(Total 6 marks)

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Q13. The maker of an electronic games player needs someone to supply the plastic case. Four companies have been asked to give details of the case they could make. These details are given in the table.

Company Cost of each case in pence

Strength

Mass of plastic used to make the case

in grams

Percentage of plastic wasted

per case

A 230 8 out of 10 410 3

B 275 9 out of 10 550 2

C 400 6 out of 10 320 4

D 300 5 out of 10 250 5

(a) One observation that can be made from the table is that as the strength increases the percentage wastage decreases.

Suggest two observations that could be made about the mass of the cases.

1. ..................................................................................................................

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2. ..................................................................................................................

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(b) Companies A, B and C use plastic made from crude oil to make their cases. Company D uses a bioplastic made from sugar cane to make its cases.

Suggest one environmental advantage and one environmental disadvantage of using bioplastics.

Advantage ....................................................................................................

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Disadvantage ...............................................................................................

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(c) Which company, A, B, C or D, would make the case that is the best value for money?

Explain why you have chosen this company.

Company .....................................................................................................

Explanation ..................................................................................................

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(Total 6 marks)

Q14. In 1939 Roy Plunkett opened the valve on a new cylinder of tetrafluoroethene gas. No gas came out!

He cut the cylinder open and found that the gas had changed into a white solid. This solid was an addition polymer.

(a) Give the name of the addition polymer that formed inside the cylinder.

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(b) The structure of this polymer can be represented by the diagram below.

Draw the structure of the monomer, tetrafluoroethene, from which it is formed.

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(c) Describe how this addition polymer forms from monomers.

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Q15. This question is about the use hydrocarbons and the production of compounds from hydrocarbons.

(a) The equation shows a reaction involving hydrocarbons.

C8H18 C2H4 + C6H14 Hydrocarbon J Hydrocarbon K Hydrocarbon L

Choose the correct processes from the box to complete the sentences.

combustion hydration thermal decomposition polymerisation

(i) Hydrocarbons K and L are produced by ........................................... . (1)

(ii) Ethanol can be produced from hydrocarbon K by .............................. . (1)

(iii) Describe a test to distinguish between hydrocarbons K and L and give the result of the test.

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(b) Hydrocarbon J burns completely in oxygen to produce carbon dioxide and water vapour.

2 C8H18 + 25 O2 16 CO2 + 18 H2O

(i) When 114g of hydrocarbon J burns completely in 400g of oxygen it produces 162g of water vapour.

What mass of carbon dioxide would be produced from burning 114g of hydrocarbon J?

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Show clearly how you work out your answer

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Answer = ................................. g (2)

(ii) The mass of carbon dioxide produced is greater than the 114g of hydrocarbon J that was burned. Explain why.

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(c) Two different processes are used to produce ethanol.

Process 1 Process 2

Fermentation of a sugar solution by yeast in a reaction vessel.

The reaction vessel has to be emptied, cleaned and refilled every few days.

The process produces a 15% ethanol solution in water.

Reaction of ethene (from crude oil) with steam in a reactor.

The reaction is only stopped if there is a fault in the reactor.

The process produces 100% ethanol.

(i) Give one advantage that Process 1 has over Process 2.

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(ii) What advantages to a manufacturer of ethanol, does Process 2 have over Process 1?

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