Q1.€€€€€€€€€ Fuel scientists develop and blend fuels for...

Q1. Fuel scientists develop and blend fuels for use in motor vehicles.

A good fuel has the following characteristics:

• volatile • easy to ignite • produces a large amount of energy when it burns • produces the minimum amount of pollution.

Information about some of the hydrocarbons that are found in petrol is given in the table.

Name Chemical formula Melting point in °C Boiling point in °C

Butane C4H

10 −138 0

Pentane C5H

12

−130 36

Hexane C6H

14 −95 69

(a) (i) Which hydrocarbon in the table is a gas at room temperature?

............................................................................................................. (1)

(ii) Hydrocarbons are compounds with low boiling points.

Explain why hydrocarbons have low boiling points.

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............................................................................................................. (2)

(b) Heptane is a hydrocarbon. It has molecules containing 7 carbon atoms.

Suggest the chemical formula for heptane.

...................................................................................................................... (1)

(c) A fuel scientist recommended increasing the amount of butane and decreasing the amount of hexane in petrol that is used in the UK in winter.

Use the information in the table to explain why.

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(d) Balanced equations for the complete combustion of butane and pentane are given below.

C4H

10 + 6½O

2 → 4CO

2 + 5H

2O

C5H

12 + 8O

2 → 5CO

2 + 6H

2O

(i) Write a balanced equation for the combustion of hexane.

............................................................................................................. (1)

(ii) Describe the pattern in the number of molecules in these equations.

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(e) Suggest why incomplete combustion occurs in a car engine.

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(Total 10 marks)

Q2. Crude oil is a mixture of alkanes from which useful fuel fractions can be obtained.

Fraction A hydrocarbon in

this fraction Boiling point of

alkane in °C

petroleum gases Propane –42

petrol (gasoline) Octane +126

paraffin (kerosene) Dodecane +216

diesel Eicosane +344

(a) (i) Suggest the lowest temperature to which crude oil needs to be heated to vaporise all of these fuel fractions.

Temperature ................................................ °C (1)

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

Temperature ................................................ °C (1)

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(iii) Describe what happens in a fractionating column that allows these fractions to be collected.

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(b) Propane is a fuel because it burns in air releasing heat energy.

(i) Complete the balancing of the two chemical equations for propane burning in air.

2C3H

8 + ......... O

2 → ......... CO

2 + ......... H

2O

2C3H

8 + ......... O

2 → ......... CO + ......... H

2O

(2)

(ii) The products of the two chemical reactions in (b)(i) are different.

Explain why.

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(Total 9 marks)

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Q3. Since 2000 there has been a lot more research into alternative, environmentally-friendly fuels for road transport.

Several pollutants are found in the exhaust emissions produced when fossil fuels are used for road transport.

Carbon monoxide (CO) interferes with the way that red blood cells carry oxygen. Carbon dioxide (CO

2) increases the level of carbon dioxide in the atmosphere and causes global warming.

Oxides of nitrogen (NOx) are produced at high temperatures when nitrogen and oxygen from the

atmosphere combine.

Sulfur dioxide (SO2) is produced when sulfur impurities in the fuel combine with oxygen in the

atmosphere.

Tiny particles of solids are produced when the fuel does not burn completely.

This increases the level of particulates (PM10) in the atmosphere.

(a) Name the environmental effect caused by:

(i) oxides of nitrogen (NOx) and sulfur dioxide (SO

2)

.......................................................................................................................... (1)

(ii) the increased level of particulates (PM10).

.......................................................................................................................... (1)

(b) Diesel obtained from crude oil is often called fossil diesel. Biodiesel can be made from many vegetable oils. One research project compared the exhaust emissions when fossil diesel or biodiesel were used as fuels.

Some of the relative amounts of these exhaust emissions are shown in the bar chart.

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(i) Use your knowledge and the information above to explain the environmental benefits of using biodiesel as a sustainable, low pollution fuel.

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(ii) Biodiesel is called a green fuel.

This is because the life-cycle emission of carbon dioxide from biodiesel is less than that from fossil diesel.

Use your knowledge and the information above to explain why biodiesel’s contribution to global warming is considered to be much less than that of fossil diesel.

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(Total 8 marks)

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Q4. Crude oil is the source of many useful materials. Crude oil is separated into fractions by fractional distillation.

(a) Describe how the naphtha fraction separates from the other fractions.

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..................................................................................................................................... (2)

(b) The naphtha fraction is often used to make other useful materials.

This involves the cracking of hydrocarbons in the naphtha fraction.

For example:

decane → hexane + ethene

C10

H22

→ C6H

14 + C

2H

4

(i) Balance the symbol equation given above. (1)

(ii) Describe how cracking is carried out.

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........................................................................................................................... (2)

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(iii) Why does ethene have different chemical properties from decane and hexane?

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........................................................................................................................... (2)

(c) Ethene is used as the starting material for many polymers. The most common polymer is poly(ethene). One hydrocarbon molecule in poly(ethene) will contain thousands of carbon atoms.

Complete the diagram to show the bonds in ethene.

H H

C C

H H (1)

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(d) Read the following information.

You are asked to decide which option for the disposal of poly(ethene) will be put forward in your area. You decide that recycling is the best option.

Suggest one economic argument and one environmental argument that will be made against recycling.

Landfill, Incineration, Recycling and Re-use of Poly(ethene)

People could be encouraged to re-use their poly(ethene) bags and containers.

Recycling poly(ethene) saves raw materials and energy needed to make new plastic. When polymers are recycled the plastics must be collected, transported, sorted into different types by hand and washed. This requires the use of fossil fuels and is expensive.

Poly(ethene) can be burnt in an incinerator with other household waste. The heat released could be used to make steam to drive an electric generator. Surplus heat could be used to heat greenhouses used for growing vegetables. Incineration at too low a temperature can produce harmful substances. The residue (ash) has to go to landfill.

Landfill is probably the easiest way to dispose of polymers and it is cheap. Polymers are often mixed in with other household rubbish. Household waste does not get sorted into different materials because it is disposed of in the same hole in the ground. When the hole is eventually full, the waste is covered by a layer of soil to stop it smelling. The waste gets compressed under its own weight. Most polymers, such as poly(ethene), are not biodegradable so will remain in the ground forever.

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For each argument made, how will you persuade those making the argument to accept your option?

(You must use only one sentence for each argument made against your decision and only one sentence for your response to it.)

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(Total 12 marks)

Q5. A large reservoir is surrounded by trees. Planners need to protect the environment. The distance around the reservoir is many kilometres. There will be only one road access to a car park a few kilometres from the reservoir. From the car park people would be transported to accommodation, activities or places of interest by steam train.

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(a) Coal contains carbon and small amounts of sulfur. The steam train would cause environmental problems if coal were used as the fuel.

Explain why.

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(b) The planners have stated that, as a result of using the steam train, there must be no overall increase of carbon dioxide added to the atmosphere. The steam train would be considered as ‘carbon neutral’ if wood, from the surrounding forest, were used as the fuel.

Suggest why.

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(Total 7 marks)

Q6. Crude oil is a mixture of mostly alkanes.

(a) Crude oil is separated into useful fractions by fractional distillation.

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(i) Describe and explain how the mixture of alkanes is separated by fractional distillation.

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(ii) The table gives the name and formula for each of the first three alkanes.

Complete the table to show the formula of butane.

(1)

Name of alkane Formula

Methane CH4

Ethane C2H

6

Propane C3H

8

Butane

(b) The structural formula of methane, CH4, is:

H │

H C H │ H

Draw the structural formula of propane, C3H

8

(1)

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(c) The relative amounts of and the market demand for some hydrocarbons from the fractional distillation of crude oil are shown in the graph.

(i) Why is the market demand for the C5 – C

8 fraction higher than the market demand for

the C21 – C

24 fraction?

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.......................................................................................................................... (1)

(ii) Cracking is used to break down large hydrocarbon molecules into smaller hydrocarbon molecules.

Complete the symbol equation by writing in the formula of the other hydrocarbon.

C20

H42 C

16H

34 + 2 ..........................................

(1)

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(iii) The C5 – C

8 fraction has low supply and high market demand.

Suggest three ways in which the oil industry could overcome this problem.

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(Total 10 marks)

Q7. 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 ethanol–petrol 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, C2H

5OH, burns to release heat energy.

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

C2H

5OH + 3O

2 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.

Ethene is then converted into ethanol.

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

.......................................................................................................................... (1)

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(ii) Complete the structural formula for ethene, C2H

4.

C C (1)

(iii) Name the compound that is added to ethene to produce ethanol, C2H

5OH.

.......................................................................................................................... (1)

(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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Q8. To make crude oil more useful it is separated into different fractions.

(a) Complete the gaps in the following sentences.

Crude oil is separated into different fractions by a process called ............................

.................................. . Each fraction has a different ............................................... . (2)

(b) Each fraction is a mixture of compounds. Most of these compounds are hydrocarbons, made up of the elements hydrogen and carbon.

(i) Explain the difference between a mixture and a compound.

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(ii) Explain the difference between a compound and an element.

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(Total 6 marks)

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Q9. Crude oil is a complex mixture of hydrocarbons, mainly alkanes. The number of carbon atoms in the molecules ranges from 1 to over 100.

(a) How does the boiling point change as the number of carbon atoms in the molecules increases?

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..................................................................................................................................... (1)

(b) Name the method used to separate petroleum into fractions.

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(c) The simplest hydrocarbon is methane, CH4. Its structure can be represented:

Draw the structure of ethane, C2H

6.

(1) (Total 3 marks)

Q10. Crude oil is obtained by drilling into the Earth’s crust. The diagram shows a section through the Earth’s crust to show how this is done.

(a) Crude oil contains many hydrocarbons. Which elements do hydrocarbons contain?

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(b) The crude oil is separated by fractional distillation. The diagram shows a column used for this.

(i) Explain, as fully as you can, how fractional distillation works.

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(ii) Naphtha burns more easily than diesel oil. Explain why.

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(iii) Naphtha contains a saturated hydrocarbon with the formula C7H

16 .

Draw the structural formula of this compound.

(2)

(Total 7 marks)

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Q11. The diagrams show the percentages of the four main fractions produced from two samples of crude oil, A and B.

(a) The light fraction contains hydrocarbons used for the manufacture of useful chemicals such as polymers. Which one of the samples, A or B, would be more useful for the manufacture of polymers? Explain your answer.

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(b) Heptane (C7H

16), is one of the hydrocarbons used for the manufacture of poly(ethene). The

first stage of the process is the production of ethene and another hydrocarbon from heptane.

C7H

16 → +

heptane ethene

(i) In the box, draw the structural formula of the other hydrocarbon produced. (1)

(ii) Describe how the reaction is carried out.

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(Total 5 marks)

Q12. The table shows how much carbon dioxide is produced when you transfer the same amount of energy by burning coal, gas and oil.

(a) Use the information from the table to complete the bar-chart. (2)

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(b) The second bar-chart shows how much sulphur dioxide is produced by burning the same three fuels.

Compare the amount of sulphur produced by burning gas with the amount produced by burning coal.

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(c) Burning fuels also produces nitrogen oxides, even though the fuels contain no nitrogen. Explain why this happens.

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..................................................................................................................................... (2)

(d) When you release the same amount of energy from coal, gas and oil, different amounts of carbon dioxide are produced. Use the information below to explain why.

(3)

(e) What other element do coal and oil usually contain?

..................................................................................................................................... (1)

(Total 9 marks)

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M1. (a) (i) butane 1

(ii) because there are weak forces (of attraction) between molecules not weak bonds

1

less energy needed (to boil) 1

(b) C7H

16

1

(c) butane is more volatile or lower boiling point or is easier to ignite or hexane is less volatile or higher boiling point or is harder to ignite

ignore reference to melting point 1

because fuel needs to be more volatile or turn to gas easier or ignites more easily in cold weather

1

(d) (i) C6H

14 + 9½O

2 → 6CO

2 + 7H

2O

equation must be completely correct 1

(ii) oxygen increases by 1 ½ 1

carbon dioxide increases by 1 and water increases by 1 1

(e) not enough oxygen 1

[10]

M2. (a) (i) 344 – 350(°C) 1

(ii) 216(°C) 1

(iii) the vapours / gases cool as they rise up the fractionating column

1

which causes the vapours / gases to condense 1

at different temperatures or into fractions that have different boiling points

1

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(b) (i) 10 6 + 8 1

7 6 + 8 1

(ii) first reaction is complete combustion accept first reaction has excess/enough oxygen

1

second reaction is incomplete combustion accept second reaction has limited oxygen

1 [9]

M3. (a) (i) acid rain

accept consequences of acid rain allow asthma / bronchitis ignore toxic gas

1

(ii) global dimming accept dimming alone

1

(b) (i) sustainable:

maximum two from:

• crops (that produce oil) can be grown in most places owtte

• renewable

• use less fossil fuels / diesel

• use (refined) waste oils

low pollution:

maximum two from:

ignore references to CO2 here

• most emissions are lower or any two named emissions from CO / SO2 / PM

10

are lower

• much / lot less SO2 emissions (than the others) owtte

• accept spillages / waste is biodegradable

• less new CO2 or (more) carbon neutral

3

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(ii) plants / photosynthesis use carbon (dioxide) from the air* 1

it / biodiesel releases carbon (dioxide) from plants / crops / photosynthesis* (*) allow 1 mark for biodiesel is (more) carbon neutral

1

(fossil) diesel releases ‘locked up’ / new carbon (dioxide) / doesn’t absorb CO

2 / absorbed it millions of years ago

1 [8]

M4. (a) any two from:

• naphtha has a different / low(er) boiling point accept different volatility

• condenses at a different temperature / height_ / place in the column / when it reaches it’s boiling point

• different size of molecules 2

(b) (i) C10

H22 → C

6H

14 + 2C

2H

4

allow multiples 1

(ii) (hydrocarbon) heated / vapours 1

(passed over a) catalyst / alumina / porous pot ignore other catalysts

1

(iii) it / ethene is unsaturated or decane and hexane / they are saturated

accept decane and hexane are alkanes / CnH

2n+2

or ethene is an alkene / CnH

2n

or different homologous series / general formula 1

ethene has a double (carbon carbon) bond or decane and hexane have only single (carbon carbon) bonds

accept ethene has a reactive double (carbon carbon) bond for 2 marks

1

(c) all bonds drawn correctly

1

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(d) economic argument against recycling

any one from:

• poly(ethene) / plastic must be collected / transported / sorted / washed

• this uses (fossil) fuels which are expensive 1

environmental argument against recycling

any one from:

• uses (fossil) fuels that are non-renewable / form CO

2 / CO / SO

2 / NO

x / particulates

ignore pollution / harmful gases / etc

• washing uses / pollutes water 1

counter arguments

any two from:

• collect / transport alongside other waste

• use biofuels (instead of fossil)

• landfill is running out

• landfill destroys habitats

• incinerators are expensive to build

• saves raw materials / crude oil

• saves energy needed to make new plastic

• incinerators may produce harmful substances

• incinerator ash goes to landfill

• poly(ethene) is non-biodegradable

• poly(ethene) can be made into other useful items

• more jobs / employment for people 2

[12]

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M5. (a) any two environmental problems with linked explanations

• global warming (1) accept effects of global warming

caused by (formation of) carbon dioxide / greenhouse gas (1) ignore greenhouse effect

• acid rain (1) accept effects of acid rain ignore respiratory problems

caused by ( formation of) sulfur dioxide (1) accept sulfur oxide ignore sulfuric acid

• global dimming (1) ignore respiratory problems

caused by ( formation of) particles / particulates / fires / smoke / carbon / pm 10 (1)

• scarring of landscape (1)

caused by mining / quarrying of coal (1) ignore ozone layer

max 4

(b) any three from:

• replant the trees / renewable / sustainable ignore reusable

• carbon dioxide is used by the trees / photosynthesis accept trees absorb carbon dioxide as they grow do not allow respiration

• it’s a (continuous carbon) cycle accept ‘carbon dioxide goes back into the air’ accept trees use CO

2 which is released when trees are burnt

• no ‘new’ carbon (dioxide) is produced or no locked up carbon (dioxide) is released

accept no carbon (dioxide) from fossil fuels is produced 3

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M6. (a) (i) heat / evaporate the crude oil / change to gas or vapour

do not accept heat with catalyst 1

cool / condense (hydrocarbons) allow small molecules at top and / or large molecules at bottom

1

at different temperatures / boiling points if the answer describes cracking ‘ no marks

1

(ii) C4H

10

1

(b) H H H │ │ │ H ─C ─ C ─ C ─ H │ │ │ H H H

1

(c) (i) C5 to C

8 fraction are fuels or easier to burn or petrol (fraction)

accept C21 to C

24 fraction not useful as fuels

do not accept produce more energy 1

(ii) C2H

4

do not accept C4H

8

1

(iii) any three from:

• use different / lighter crude oils

• develop markets for low demand fractions

• develop new techniques / equipment to use low demand fractions as fuels

• cracking

• convert low demand fractions to high demand fractions or bigger molecules to smaller molecules

• develop alternative / bio fuels do not accept price

3 [10]

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M7. (a) (i) by (fractional) distillation

accept a description of the distillation process (heat and how separation works) eg heat and condense accept boil / vapourise etc for heat

or

fractionation 1

(ii) CO2

note the order of these products must be correct 1

H2O

wrong way round = 1 mark 1

(b) (i) (hexane) has been broken down (into smaller hydrocarbons / molecules) 1

accept (thermal) decomposition / cracked / split / broken up owtte

(ii) H H │ │ C = C │ │ H H

accept CH2 = CH

2

1

(iii) water / hydrogen oxide / steam accept H

2O

1

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(c) candidates must include both sugar cane and crude oil in their evaluation and both an advantage and a disadvantage to gain full marks. if they do not then the maximum mark is three

any four from:

advantages of using sugar

• country has no wealth to buy (large quantities of) crude oil not ‘expensive’ alone

• country has limited technological development

or

underdeveloped / third world country

• able / suitable climate to grow sugar cane

• enough land to grow sugar cane / land cannot be used to grow food / deforestation

• sugar is a renewable source

or

crude oil is a non-renewable resource / finite resource / limited resources

• CO2 / carbon neutral

advantages of using alkanes:

• economic costs are low

• continuous process

• country has large oil resources

• country has oil refineries / cracking plants

• very pure product

• faster process 4

[10]

M8. (a) fractional distillation 1

boiling point or use 1

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(b) (i) mixture: compounds or elements or substances together but not chemically combined

ignore references to separation 1

compound: (different) elements or different atoms together and chemically combined

ignore references to separation 1

(ii) element: contains only one type of atom accept made of atoms which contain the same number of protons

1

compound: contains different types of atom chemically combined ‘chemically combined’ not needed here if already stated in (b)(i)

1 [6]

M9. (a) the more C atoms the higher the b.pt./temperature Allow just higher. Not answer based on melting point

for 1 mark 1

(b) (fractional) distillation/fractionation for 1 mark

1

(c)

must include H atoms and lines not CH3 – CH

3

for 1 mark 1

[3]

M10. (a) hydrogen and carbon

for 1 mark 1

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(b) (i) the oil is evaporated / boiled / liquid converted to gas / vaporised

oil is condensed/changed back to liquid/cooled below boiling point (not just cooled)

liquids of different boiling points condense at different levels / fractions with lower boiling points form near the top / boiling point linked to chain length or Mr

each for 1 mark 3

(ii) Assume they mean naphtha unless they say otherwise. smaller molecules /contains less atoms /lower boiling point /more volatile /less bonds to break /lower activation energy

If the answer is given the opposite way around then diesel must be specified.

any one for 1 mark 1

(iii)

correct number of atoms = 1 correct number of bonds (attached to correct atoms) = 1 Accept diagrams which show electrons correctly. CH

3CH

2CH

2CH

2CH

2CH

2CH

3 = 1

for 2 marks 2

[7]

M11. (a) B because it contains more of the light fraction) 1

Quantitative answer e.g. B has 30%, A has 20% / 10% more / 1.5 times more

1

(b) (i)

1

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(ii) heat 1

catalyst if neither mark gained allow cracking for 1 mark

1 [5]

M12. (a) both bars correct height_ (to better than half a square)

1 mark for both

both bars correctly labelled (w.r.t. relative height_s if these incorrect)

for 1 mark 2

(b) a lot less / much less / 18 times less (converse must specify coal) gains 1 mark

1

(c) ideas that

• at high temperatures (produced when fuels burn)

• nitrogen and oxygen from air / atmosphere combine / react or nitrogen from air / atmosphere oxidises

for 1 mark each 2

(d) ideas that

• coal produces most carbon dioxide / more CO2 than gas / oil

• because coal is (mostly) carbon

• gas produces less carbon dioxide than coal / oil

• oil and gas also contain hydrogen / contain more hydrogen atoms than carbon atoms / also produce water

any three for 1 mark each 3

(e) sulphur for 1 mark

2 [9]

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Q1.€€€€€€€€€ Fuel scientists develop and blend fuels for...

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