Hydrocarbons: Fuel & Feedstock (AQA GCSE Chemistry: Combined Science)

Exam Questions

2 hours14 questions
1a2 marks

This question is about crude oil.

Crude oil is made up of hydrocarbons. 

Name the two elements in a hydrocarbon

1b1 mark

Which word best describes crude oil? 

Tick () one box. 

 Element  
 Compound  
 Mixture  
1c4 marks

Complete the sentences to describe how crude oil is formed. 

Use the answers in the box. 

high air pressure thousands plankton
millions temperature trees  


Crude oil is formed from the remains of dead plants and animals such as ____________________.

Over ___________________  of years it is buried under mud and exposed to high ____________________ and ____________________. 

1d1 mark

Crude oil is a finite resource.

What is meant by the term finite

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2a2 marks

This question is about alkanes.

Draw one line from the name of the alkane to the correct displayed formula. 

ethane-butane

2b1 mark

What is the general formula of alkanes?

Tick () one box.

 CnH2n  
 CnH2n+1  
 CnH2n+2  
2c1 mark

Crude oil is a mixture of alkanes.

Name the process used to separate this mixture.

2d2 marks

Alkanes undergo complete combustion reactions.

Complete the equation to show the complete combustion of methane. 

methane    +   ______________   →  carbon dioxide   +   ________________

2e1 mark

What type of bond is formed between the carbon and hydrogen atoms in an alkane?

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3a1 mark

This question is about fractional distillation.

Which property of the fractions allows crude oil to be separated this way? 

Draw a circle around the correct answer. 

 Boiling point Flammability Viscosity
3b2 marks

The fractions produced by fractional distillation have different properties. 

Figure 1 shows the locations that fractions condense at.

Figure 1

aqa-gcse-7-1e-tq3b-fractional-distillation

Tick () two properties of Fraction 1.

 Easy to ignite  
 High boiling point  
 Contains hydrocarbons  
 Large number of carbon atoms  
3c2 marks

Give the names of two fractions produced by fractional distillation. 

3d5 marks

Complete the sentences using the words in the box to describe the process of fractional distillation.

cool heated low temperatures
evaporate    distilled  condense energy levels


The crude oil is ___________________ and the hydrocarbons _______________.   The vapours rise up the column. 

They __________________ and ________________ at different _____________________. 

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4a2 marks

This question is about cracking.

Long chain hydrocarbons can be cracked to produce shorter chain alkanes and alkenes.

Figure 1 shows the structure of an alkane and an alkene. 

Figure 1

aqa-gcse-7-1e-tq4a-alkane-alkene

Give two differences between an alkane and an alkene.

4b1 mark

The following word equation shows the cracking of a a long chain hydrocarbon into a shorter alkane and alkene.

C5H12        →        C3H8      +     C2H4

Name the hydrocarbon with the formula C3H8.

Circle one answer. 

ethane propane propene
4c1 mark

Explain why cracking is carried out.

4d1 mark

Give one use of the alkanes produced from cracking. 

Tick () one box. 

 As a polymer  
 As a fuel  
 As a solvent  
4e2 marks

Give two conditions of catalytic cracking.

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5a2 marks

This question is about organic chemistry. 

Crude oil consist of hydrocarbons such as ethane.

Complete the displayed formula of ethane. 

C - C

5b2 marks

Alkanes of similar length can be separated using fractional distillation in a lab. 

Figure 1 shows the set up of equipment.

aqa-gcse-7-1e-tq5b-fractional-distillation-lab

The change of state at A is: ____________________. 

The change of state at B is: ____________________.

5c1 mark

The long chain fractions produced from fractional distillation can be broken down into shorter chained alkanes and alkenes. 

Complete the chemical equation for the cracking of hydrocarbon, C15H32.

C15H32    →   C8H18   +   ________   +    C2H4

5d2 marks

To distinguish between alkanes and alkenes, bromine water can be added. 

Draw one line from each hydrocarbon to give the colour change that would be observed if bromine water was added.testing-for-alkenes

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1a6 marks
Crude oil is a fossil fuel and is extracted from below the Earth's surface. 

It contains many useful substances which are separated into fractions before further processing. 

Describe the process of separation of crude oil in as much detail as possible.

1b4 marks

Often long chain alkanes are produced from the fractional distillation of crude oil. 

These then undergo a process called cracking to produce other compounds. 

Explain why this is done and include the products of cracking in your answer.

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2a2 marks

The table displays information about the formula mass and boiling point of some alkanes.

Name

Formula

Relative formula mass

Boiling point in °C

methane

CH4

16

–160

ethane

C2H6

30

–90

propane

 C3H8

44

–40

   

58

 

pentane

C5H12

72

36

hexane

C6H14

86

68


Give the formula of and name of the compound that is missing.

2b1 mark

Describe the relationship between the relative formula mass and boiling point.

2c3 marks

Plot the points from the table on Figure 2 and draw a best fit line.

Figure 2

7-1-hydrocarbons-fuel--feedstock-medium-q2c

2d2 marks

Use the graph to determine the boiling point of butane, showing clearly how you arrived at your answer.

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3a2 marks

Most hydrocarbons extracted from crude oil are alkanes.

Long chain alkanes are routinely cracked to produce more useful molecules.

The equation shows the cracking of dodecane.

C12H26 → C4H10 + C6H12 + C2H4

Give two conditions necessary to crack large alkane molecules.

3b3 marks

State whether C12H26 has a higher boiling point than C6H12 and explain why.

3c1 mark

Two of the products formed in the reaction in part (a) are alkenes.

Describe the colour change you would see when bromine water is added to an alkene.

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4a2 marks

Crude oil can be separated into different fractions which contain molecules with a similar number of carbon atoms.

These fractions undergo further processing to produce fuels and feedstock for the petrochemical industry.

State two fuels that are obtained from crude oil.

4b2 marks

Fractions from crude oil can also be processed to produce feedstock for the petrochemical industry.

Many of the materials we use in everyday life are produced by the petrochemical industry.

State two useful substances that are produced by the petrochemical industry.

4c
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3 marks

Figure 1 shows the percentage by mass of different fractions in a sample of crude oil.

Figure 1

composition-of-crude-oil

Calculate the mass of diesel oil that can be obtained from 5000 kg of crude oil.

4d
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3 marks

What mass of crude oil is needed to obtain 5700 kg of petrol?

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5a3 marks

Saturated hydrocarbons are fuels.

Write down the balanced equation for the complete combustion of propane, C3H8.

______   +  _____    →   _____   +   _____

5b2 marks

Naphtha is a fraction obtained from crude oil with the formula C7H16.

Draw the displayed formula of naphtha.

5c3 marks

Hexadecane, C16H34, is also another hydrocarbon that can be obtained from crude oil.

How would you expect the boiling point of hexadecane to differ from the boiling point of naphtha?

Explain your answer.

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1a4 marks

This question is about the processes and reactions which occur in the petrochemical industry. 

Figure 1 shows some of these processes and reactions. 

Figure 1

aqa-gcse-7-1h-tq1a-petrochemical-industry-processes

Describe how crude oil is separated into fractions.

1b2 marks

Describe the conditions required in reactor 1

1c2 marks

Ethene is used to produce the polymer poly(ethene) in reactor 2.

Ethene is a gas at room temperature but poly(ethene) is a solid.

Explain the difference in physical state.

1d4 marks

Compare the properties of gasoline and fuel oil. 

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2a1 mark

This question is about cracking. 

Cracking is used to break down large alkanes into smaller hydrocarbons.

A long chain alkane is cracked to produce the following products:

C20H42    →     C12H26    +  C5H10   +   C3H6

Suggest one use of the product with the formula C3H6. 

2b1 mark

The market demand for shorter chain alkanes is greater than the market demand for long chain alkanes.

Suggest one reason why.

2c3 marks

Short chain fractions have low supply and high market demand.

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

2d2 marks

C20H42 can also be cracked to give C16H34 and ethene, C2H4.

Write a balanced symbol equation for this reaction. 

2e1 mark

When bromine water is added to the products of the reaction in part (d), one of the products forms a colourless solution. 

Draw the displayed formula of the product that produces this colourless solution.

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3a1 mark

This question is about the reactions of alkanes.

Decane can be cracked to form the alkene, propene, C3H6, and one other product in the following reaction:

C10H22   →   __________   +  C3H6

Give the formula of the other product formed. 

3b3 marks

Describe and give the result of a chemical test that would distinguish between the two products. 

3c2 marks

Describe how catalytic cracking is carried out. 

3d2 marks

Explain why decane is a saturated hydrocarbon.

3e2 marks

Another alkane, butane, can undergo the following combustion reactions:

         Equation 1:  2C4H10 + 13O2 ⟶ 8CO2 + 10H2O

         Equation 2:     2C4H10 + 5O2 ⟶ 8C + 10H2O

Explain why different products are made.

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4a3 marks

This question is about crude oil and the hydrocarbons obtained from it. 

Describe how crude oil is formed.

4b1 mark

Table 1 shows some alkanes that are found in crude oil. 

Table 1 

Alkanes Boiling point in oC
 C5H12 36
C7H16 98
C10H22 174


What is the general formula for alkanes? 

4c2 marks

Write the balanced symbol equation for the complete combustion of C7H16

4d3 marks

Explain the trend in boiling points of the alkanes.

4e2 marks

A student was investigating the properties of the alkanes shown in Table 1 in part (a) using the following method:

   1) Pour 20 cm3 of C5H12 into a funnel 

   2) Open the tap and start a stopwatch 

   3) When the level of C5H12 reaches line X stop the stopwatch 

   4) Repeat steps with the other two alkanes 

The diagram in Figure 1 shows the apparatus used.

Figure 1

hydrocarbon-viscosity-experiment

C5H12 took 5.3 seconds to reach line X.

Explain the trend you would expect to see when the student repeats the method with the other two alkanes.

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