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Cracking and alkenes

Edexcel IGCSE Chemistry

Topic questions Organic chemistry Cracking & alkenes

Cracking & alkenes

14 questions · 165 marks · about 3 hours

Cracking and alkenes questions

TopicCracking & alkenes

Chemistry Paper 2 November 2024, Question 6 13 marks

This question is about crude oil.

(a)

Describe how crude oil is separated into fractions by fractional distillation.

[4]

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(b)

Some of the long-chain alkanes obtained from fractional distillation are cracked, producing shorter-chain alkanes and ethene.

(b)(i)

Give the conditions necessary for cracking to occur.

[2]

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(b)(ii)

Explain why shorter-chain alkanes are more useful than longer-chain alkanes.

[2]

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(b)(iii)

Ethene reacts with bromine.

The equation shows the displayed formulae of the reactants and product.

H H

$Question 6, shown as an image$

Br Br

The table shows some bond energies.

Bond	Bond energy in kJ/mol
C C	612
C C	348
C H	414
Br Br	193
C Br	276

Show that the molar enthalpy change, Δ H, for this reaction is about –100 kJ/mol.

ΔH =_........ kJ/mol

[3]

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(b)(iv)

Explain why the reaction between ethene and bromine is exothermic.

Refer to bond energies in your answer.

[2]

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Chemistry Paper 1 June 2024 (R), Question 8 11 marks

This question is about crude oil.

(a)

Describe how crude oil is separated into fractions by fractional distillation.

[4]

Reveal mark scheme

(b)

Some of the products of fractional distillation are then cracked.

This equation represents a reaction that occurs during cracking.

$Question 8, shown as an image$

Explain why cracking is an important process in the oil industry.

[4]

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(c)

Fuels obtained from crude oil may contain impurities.

Explain how an impurity found in fuels can cause an environmental problem.

[3]

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Chemistry Paper 2 June 2024, Question 3 11 marks

The diagram shows the separation of crude oil into fractions.

(a)

Give the name of fraction A and the name of fraction F.

fraction A

[2]

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(b)

fraction F

One of the fractions is kerosene.

(b)(i)

Give one use of kerosene.

[1]

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(b)(ii)

Describe how kerosene can be obtained from crude oil.

[3]

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(c)

Catalytic cracking is a process used to break down fractions containing long‑chain molecules.

(c)(i)

Give the name of the catalyst and the temperature used for catalytic cracking.

catalyst

[2]

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(c)(ii)

temperature

Explain why catalytic cracking is useful.

[3]

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Chemistry Paper 1 November 2023, Question 3 12 marks

Also involves Intermolecular forces

Crude oil is an important source of organic compounds.

(a)

The diagram shows how crude oil can be separated into useful mixtures of hydrocarbons.

(a)(i)

Give the name of this method of separation.

[1]

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(a)(ii)

State what happens to the crude oil when it is in X.

[1]

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(a)(iii)

Give the letter of the mixture that is most likely to contain a hydrocarbon with six carbon atoms.

[1]

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(a)(iv)

Give the name of mixture D.

[1]

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(a)(v)

Give a use for mixture B.

[1]

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(b)

Explain, in terms of intermolecular forces, why a hydrocarbon in mixture B has a higher boiling point than a hydrocarbon in mixture D.

[3]

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(c)

Catalytic cracking can be used to break down long‑chain hydrocarbons to produce shorter‑chain alkanes and alkenes.

(c)(i)

Give the name of a catalyst used in catalytic cracking.

[1]

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(c)(ii)

Complete the equation to show two different alkenes that could be produced in this cracking reaction.

$Question 3, shown as an image$

[2]

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(c)(iii)

Give one important use for short‑chain alkenes.

[1]

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Chemistry Paper 1 June 2023 (R), Question 10 15 marks

Also involves Alcohols · Intermolecular forces

This question is about propene.

(a)(i)

The structural formula of propene is CH₃CH $fraction$ CH₂

Complete the dot-and-cross diagram for a molecule of propene.

[2]

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(a)(ii)

Describe the forces of attraction that hold the atoms together in a molecule of propene.

[2]

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(b)

The alkane pentadecane has the formula C₁₅H₃₂

Describe how propene can be produced from pentadecane.

[2]

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(c)

Propene is used to make poly(propene).

(c)(i)

Complete the equation for the formation of poly(propene).

$Question 10, shown as an image$

[2]

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(c)(ii)

Explain why the disposal of poly(propene) in landfill sites is a problem.

[2]

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(d)

Propene can be converted into compound X.

(d)(i)

Compound X contains these percentages by mass.

• carbon 60%

• hydrogen 13.3%

• oxygen 26.7%

Compound X has an M_r of 60

Determine the molecular formula of compound X.

[3]

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(d)(ii)

Propene and compound X both have simple molecular structures.

Explain why compound X has a higher boiling point than propene.

[2]

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Chemistry Paper 2 June 2023 (R), Question 4 9 marks

(a)

The diagram shows a fractionating column used to separate crude oil into fractions.

(a)(i)

Give one use for refinery gases and one use for bitumen.

refinery gases

[2]

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(a)(ii)

bitumen

Give a reason why refinery gases rise to the top of the column.

[1]

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(a)(iii)

State what must happen to the crude oil before it is pumped into the column.

[1]

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(b)

There is a low demand for some of the hydrocarbons obtained from crude oil.

Catalytic cracking can be used to convert low‑demand hydrocarbons into more useful products.

(b)(i)

Give the conditions needed for cracking.

[2]

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(b)(ii)

The cracking of tetradecane is shown in the equation.

$Question 4, shown as an image$

Explain why there is a high demand for both of the products.

[3]

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Chemistry Paper 2 January 2023, Question 4 13 marks

Fractional distillation is used to separate crude oil into fractions.

The diagram shows a fractionating column and the fractions obtained from crude oil.

(a)(i)

Describe how crude oil is separated into fractions in the fractionating column.

[4]

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(a)(ii)

Give a use for kerosene and a use for bitumen.

kerosene

[2]

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(b)

bitumen

Some fractions obtained from crude oil are cracked to form alkenes.

(b)(i)

Describe what is meant by cracking.

[2]

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(b)(ii)

Ethene is obtained by cracking.

This is the displayed formula of ethene.

Explain why ethene is described as an unsaturated hydrocarbon.

[3]

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(b)(iii)

Describe a test to show that ethene is unsaturated.

[2]

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Chemistry Paper 1 June 2022, Question 3 10 marks

Crude oil is an important source of organic compounds.

(a)

The diagram shows how crude oil can be separated into fractions by fractional distillation.

(a)(i)

State what happens to the crude oil when it is in X.

[1]

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(a)(ii)

Give the name of fraction E.

[1]

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(a)(iii)

Give a use for fraction A.

[1]

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(b)

One of the compounds in fraction D is tridecane (C₁₃H₂₈) which can be cracked to form shorter-chain hydrocarbons.

(b)(i)

State the catalyst and temperature used in this cracking reaction.

catalyst

[2]

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(b)(ii)

temperature

The equation shows an example of a catalytic cracking reaction.

$Question 3, shown as an image$

Give two reasons why this reaction is important.

[2]

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(c)

Sulfur is an impurity in crude oil. Explain why this is a problem for the environment.

[3]

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Chemistry Paper 1 June 2022 (R), Question 7 15 marks

The diagram shows some important conversion processes used in the oil industry.

(a)

Describe how kerosene is produced from crude oil in process 1.

[5]

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(b)

C₁₂H₂₆ is present in kerosene.

In process 2, C₁₂H₂₆ is cracked to produce two molecules of ethene and one molecule of another hydrocarbon.

(b)(i)

Complete the equation for the cracking of C₁₂H₂₆

$Question 7, shown as an image$

[1]

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(b)(ii)

Explain why cracking is a useful process in the oil industry.

[4]

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(c)

This is the equation for one of the reactions that may occur during process 3.

H H

$Question 7, shown as an image$

C l C l

What is the name of this type of reaction?

$Question 7, shown as an image$

[1]

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(d)(i)

[2]

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(d)(ii)

Explain why the disposal of polymers such as poly(chloroethene) is difficult.

[2]

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Chemistry Paper 2 January 2022 (R), Question 2 10 marks

Crude oil is a mixture of hydrocarbons.

(a)

This passage is about the industrial separation of crude oil.

Complete the passage by adding the missing words.

Crude oil is_........ to form vapour.

The vapour is passed through a_........ column.

The refinery gases are collected at the top of the column because they have low

[3]

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(b)

Bitumen is collected at the bottom of the column.

Give one use of bitumen.

[1]

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(c)

One of the hydrocarbons in crude oil is an alkane with this structural formula.

$Question 2, shown as an image$

(c)(i)

Give the name of this alkane.

[1]

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(c)(ii)

Calculate the relative molecular mass (M_r) of this alkane.

[1]

(d)

Catalytic cracking is used to convert long-chain alkanes into shorter-chain alkanes.

Give the name of the catalyst and the temperature used in catalytic cracking.

[2]

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(e)

Catalytic cracking also produces alkenes.

Decane (C₁₀H₂₂) can undergo cracking to give C₄H₁₀ and two different alkenes.

Complete the equation for this cracking process.

$Question 2, shown as an image$

[2]

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Chemistry Paper 1 January 2021 (R), Question 3 13 marks

Crude oil is a mixture of organic compounds.

Most of these compounds are members of the same homologous series.

(a)

State the name of this homologous series.

[1]

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(b)

An industrial process is used to separate crude oil into fractions.

(b)(i)

The process depends on a difference in a property of the fractions.

What is this property?

$Question 3, shown as an image$

[1]

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(b)(ii)

The boxes give some uses of fractions and some names of fractions.

Draw one straight line from each use to its correct fraction.

$Question 3, shown as an image$

[3]

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(c)

Fuels obtained from the fractions may contain impurities.

Explain how the combustion of a common impurity in fuels may cause an environmental problem.

[3]

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(d)

Some of the fractions contain long-chain molecules which are not very useful.

(d)(i)

Give the name of the process used to convert long-chain molecules into more useful shorter-chain molecules.

[1]

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(d)(ii)

Give the catalyst and temperature used in the industrial process to convert long-chain molecules into shorter-chain molecules.

[2]

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(d)(iii)

When C₁₃H₂₈ is used in this process, three different molecules are formed.

Complete the equation for this reaction.

$Question 3, shown as an image$

[2]

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Chemistry Paper 2 January 2021, Question 7 14 marks

Also involves Moles and amount of substance

This question is about octane (C₈H₁₈) which is produced in the gasoline fraction during fractional distillation of crude oil.

(a)

The diagram shows a fractionating column.

Describe how crude oil is separated into fractions in the fractionating column.

[4]

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(b)

Octane can also be produced by the process of cracking.

Give the conditions for cracking.

[2]

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(c)

A car is driven at constant speed for 4.00 km.

The exhaust gases are collected and their volume at room temperature and pressure (rtp) is 5.02 × 10⁵cm³.

The exhaust gases include carbon dioxide and oxides of nitrogen.

The carbon dioxide is removed from the exhaust gases. The volume of the remaining gases at rtp is 2.96 × 10⁵cm³.

(c)(i)

Explain how oxides of nitrogen form in a car engine.

[2]

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(c)(ii)

Give a reason why oxides of nitrogen should not be released into the atmosphere.

[1]

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(c)(iii)

Show that the car produces less than 100 g of carbon dioxide per km.

[molar volume of carbon dioxide at rtp = 24 000 cm³]

[5]

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Chemistry Paper 2 November 2020 (R), Question 3 8 marks

(a)

The diagram shows a fractionating column used to separate crude oil into fractions.

(a)(i)

Give a use for bitumen and a use for gasoline.

[2]

Reveal mark scheme

(a)(ii)

Explain why bitumen is collected at the bottom of the fractionating column and gasoline is collected near the top of the fractionating column.

[2]

Reveal mark scheme

(b)

There is a low demand for some of the fractions obtained from crude oil.

Cracking can be used to convert these fractions into more useful substances.

(b)(i)

State the conditions needed for cracking.

[2]

Reveal mark scheme

(b)(ii)

Dodecane (C₁₂H₂₆) can be cracked to produce an alkane and two alkenes.

Complete the equation by giving the formulae of the two alkenes.

$Question 3, shown as an image$

[2]

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Chemistry Paper 2 January 2020, Question 2 11 marks

Crude oil is a mixture of hydrocarbons.

(a)

Name the process used to separate crude oil into fractions.

[1]

Reveal mark scheme

(b)

Give one use of the kerosene fraction.

[1]

Reveal mark scheme

(c)

One of the hydrocarbons in the refinery gas fraction is an alkane with the structural formula CH₃CH₂CH₂CH₃

(c)(i)

Give the name of this alkane.

[1]

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(c)(ii)

Calculate the relative molecular mass (M_r) of this alkane.

[1]

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(d)

One of the alkanes in the gasoline fraction has the displayed formula

H H H H H H H

$Question 2, shown as an image$

(d)(i)

Determine the molecular formula of this alkane.

[1]

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(d)(ii)

Give the general formula for the alkanes.

[1]

(e)

Catalytic cracking is used to convert long‑chain alkanes into shorter‑chain alkanes.

(e)(i)

Name the catalyst used in catalytic cracking.

[1]

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(e)(ii)

Explain why it is necessary to convert long‑chain alkanes into shorter‑chain alkanes.

[2]

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(f)

Catalytic cracking also produces alkenes.

C₁₁H₂₄ can undergo cracking to give pentane (C₅H₁₂) and two different alkenes.

Complete the equation for this cracking reaction.

$Question 2, shown as an image$

[2]

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Chemistry Paper 2 January 2022 (R), Question 2 10 marks

Chemistry Paper 1 January 2021 (R), Question 3 13 marks

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Chemistry Paper 2 November 2020 (R), Question 3 8 marks

Chemistry Paper 2 January 2020, Question 2 11 marks