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Isomerism

Edexcel IGCSE Chemistry

Topic questions Organic chemistry Isomerism

Isomerism

11 questions · 153 marks · about 3 hours

Isomerism questions

TopicIsomerism

Chemistry Paper 1 June 2025, Question 5 14 marks

Also involves Intermolecular forces

Butane (C₄H₁₀) is an alkane.

(a)

Explain why butane is a saturated hydrocarbon.

[3]

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(b)

(b)(i)

When butane burns completely in oxygen, carbon dioxide and water are produced.

Give a chemical equation for this combustion reaction.

[2]

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(b)(ii)

Incomplete combustion can occur when the oxygen supply is limited.

One product of the incomplete combustion of butane is carbon monoxide.

Give the name of another product of this incomplete combustion.

[1]

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(b)(iii)

State why carbon monoxide is poisonous to humans.

[1]

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(c)

C₄H₁₀ exists as two isomers.

(c)(i)

State what is meant by the term isomers.

[2]

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(c)(ii)

Draw the displayed formula of each isomer.

[2]

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(d)

Explain why hexane (C₆H₁₄) has a higher boiling point than butane (C₄H₁₀).

[3]

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Chemistry Paper 1 November 2024, Question 10 12 marks

This question is about alkanes and alkenes.

(a)

Ethane and ethene each react with bromine, but under different conditions.

(a)(i)

Give a reason why ethane does not undergo an addition reaction with bromine.

[1]

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(a)(ii)

Complete the equation for the substitution reaction between ethane and bromine, including an essential condition for the reaction.

$Question 10, shown as an image$

condition

[2]

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(a)(iii)

Give the colour change that occurs when ethene reacts with bromine water.

[1]

(b)

The diagram shows the displayed formulae of two compounds in the homologous series of alkenes.

$Question 10, shown as an image$

(b)(i)

Compounds in the same homologous series have the same general formula.

Give two other characteristics of compounds in the same homologous series.

[2]

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(b)(ii)

Explain why the alkenes in the diagram are isomers.

[2]

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(b)(iii)

Draw the displayed formula of another alkene that is an isomer of these two alkenes.

[1]

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(c)

The reaction used to make poly(ethene) can be represented by this equation.

$Question 10, shown as an image$

H H n

Describe the differences between the reactant and the product in this reaction.

Refer to carbon chain length, type of bond and state of matter in your answer.

[3]

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Chemistry Paper 1 November 2023, Question 5 17 marks

Also involves Moles and amount of substance

This question is about alkanes and alkenes.

(a)

The alkane C₄H₁₀ exists as two isomers.

(a)(i)

State what is meant by the term isomers.

[2]

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(a)(ii)

Draw the displayed formulae for the two isomers of C₄H₁₀

[2]

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(b)

Ethane (C₂H₆) can react with bromine.

(b)(i)

State the condition needed for ethane to react with bromine.

[1]

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(b)(ii)

Complete the equation for this reaction.

$Question 5, shown as an image$

[1]

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(b)(iii)

Give the name for this type of reaction.

[1]

(c)

Explain why ethane is described as a saturated compound.

[2]

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(d)

State what you would observe when ethane and ethene are added separately to two samples of bromine water.

ethane

[2]

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(e)

ethene

Explain why straight‑chain alkenes always have the same empirical formula, but straight‑chain alkanes have different empirical formulae.

Refer to the molecular formulae of the alkanes C₂H₆ and C₄H₁₀ in your answer.

[3]

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(f)

An organic compound has this percentage composition by mass.

C = 19.2 % H = 4.0 % O = 12.8 % Br = 64.0 %

Calculate the empirical formula of this compound.

[3]

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Chemistry Paper 1 January 2023 (R), Question 3 15 marks

This question is about alkanes.

(a)

An alkane has the structural formula CH₃CH₂CH₂CH₃

Give the missing information for this alkane.

[4]

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(b)

There are two isomers of C₄H₁₀

(b)(i)

State what is meant by the term isomers.

[2]

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(b)(ii)

Draw the displayed formula of each isomer of C₄H₁₀

Isomer 1
Isomer 2

[2]

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(c)

Methane reacts with bromine to form bromomethane and one other product.

(c)(i)

Give the formula of the other product.

[1]

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(c)(ii)

What is the name of this type of reaction?

$Question 3, shown as an image$

[1]

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(c)(iii)

State the condition needed for this reaction to occur.

[1]

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(d)

When ethane (C₂H₆) burns in a plentiful supply of air, carbon dioxide and water are formed.

(d)(i)

Give a chemical equation for this reaction.

[2]

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(d)(ii)

When the air supply is limited, incomplete combustion occurs.

Explain why a gas formed by incomplete combustion can cause a problem for humans.

[2]

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Chemistry Paper 1 January 2023, Question 7 12 marks

Also involves Amounts of substance in equations

(a)

Give a reason why compound X is not a hydrocarbon.

[1]

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(b)

Give the letter of the compound that is a saturated hydrocarbon with the empirical formula CH₂

[1]

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(c)

Give the letter of the compound that produces nine moles of water when one mole undergoes complete combustion.

[1]

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(d)

Give the structural formula of compound Y.

[1]

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(e)

Explain why compounds W and Y are isomers.

[2]

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(f)

Compound Z reacts with bromine in the presence of ultraviolet radiation.

(f)(i)

Write a chemical equation for this reaction.

[2]

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(f)(ii)

What is the name for this type of reaction?

$Question 7, shown as an image$

[1]

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(g)

Describe how the combustion of sulfur-free petrol in a car engine produces gases that can cause acid rain.

Do not refer to carbon dioxide in your answer.

[3]

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Chemistry Paper 1 June 2022, Question 5 11 marks

This question is about alkanes and alkenes.

(a)

The alkane C₅H₁₂ has three isomers.

(a)(i)

State what is meant by the term isomers.

[2]

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(a)(ii)

Calculate the relative formula mass (M_r) of C₅H₁₂

$Question 5, shown as an image$

[1]

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(a)(iii)

This is the displayed formula of one of the isomers.

H H H H H

$Question 5, shown as an image$

Give the name of this isomer.

[1]

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(a)(iv)

Draw the displayed formulae of the other two isomers.

Isomer 1
Isomer 2

[2]

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(b)

Ethane (C₂H₆) and ethene (C₂H₄) both react with bromine.

Describe the differences in the reactions of ethane and ethene with bromine.

Refer to the conditions, the products and the types of reaction involved.

[5]

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Chemistry Paper 1 January 2022, Question 8 15 marks

(a)(i)

Give the letter of a compound not shown as a displayed formula.

[1]

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(a)(ii)

Give the letter of a saturated compound with the general formula C_nH_2n

[1]

(a)(iii)

Name compound E.

[1]

(a)(iv)

Explain why compound A and compound D are isomers.

[2]

(b)

Compound F reacts with bromine in the presence of ultraviolet radiation.

(b)(i)

Complete the equation for the reaction.

[1]

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(b)(ii)

Give the name of this type of reaction.

[1]

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(c)

(c)(i)

Another compound, G, has this percentage composition by mass.

C = 37.8 % H = 6.3 % C l = 55.9 %

Show by calculation that the empirical formula of compound G is C₂H₄Cl

[3]

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(c)(ii)

The relative formula mass (M_r) of G is 127

Determine the molecular formula of G.

[2]

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(d)

Compound E is used to make an addition polymer.

(d)(i)

[2]

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(d)(ii)

Give one problem caused by the disposal of addition polymers.

[1]

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Chemistry Paper 1 January 2021 (R), Question 8 15 marks

Also involves Relative formula mass · Moles and amount of substance

(a)(i)

Organic compounds can exist as isomers.

Explain what is meant by the term isomers.

[2]

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(a)(ii)

Organic compound Q reacts with bromine, without the presence of ultraviolet radiation, to form the compound C₄H₈Br₂

Draw the displayed formulae of two isomers of Q.

[2]

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(b)

An acrylic polymer can be formed from molecules with this structure.

$Question 8, shown as an image$

(b)(i)

A student describes the molecule as an unsaturated hydrocarbon.

Explain whether this is a correct description.

[2]

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(b)(ii)

Name the type of polymerisation that occurs in the formation of the polymer.

[1]

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(b)(iii)

Complete the equation for the polymerisation reaction.

$Question 8, shown as an image$

[2]

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(c)

Octane is a compound in petrol.

The equation for the complete combustion of octane is

$Question 8, shown as an image$

(c)(i)

The fuel tank of a car contains 50.0 dm³ of octane.

Calculate the mass, in kg, of carbon dioxide formed if all the octane in the fuel tank undergoes complete combustion.

[mass of 1 dm³ of octane = 700 g]

[5]

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(c)(ii)

State an environmental problem caused by carbon dioxide.

[1]

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Chemistry Paper 1 November 2020 (R), Question 3 14 marks

This question is about alkenes and alkanes.

(a)

Complete the table by giving the missing information about the alkene with the molecular formula C₃H₆

[4]

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(b)

Alkenes are unsaturated compounds.

(b)(i)

State what is meant by the term unsaturated.

[1]

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(b)(ii)

Describe a test to show that a compound is unsaturated.

[2]

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(c)

When the alkane methane reacts with chlorine, the products are chloromethane (CH₃Cl) and hydrogen chloride gas.

(c)(i)

Give a chemical equation for this reaction.

[1]

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(c)(ii)

What is the name of this type of reaction?

$Question 3, shown as an image$

[1]

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(c)(iii)

State the condition needed for this reaction to occur.

[1]

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(d)

When ethane reacts with chlorine, one of the products of the reaction has the formula C₂H₄Cl₂

There are two isomers with this formula.

(d)(i)

State what is meant by the term isomers.

[2]

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(d)(ii)

Draw the displayed formulae of the two isomers with the formula C₂H₄Cl₂

[2]

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Chemistry Paper 1 November 2020, Question 6 14 marks

The table shows the molecular formulae of six organic compounds, A, B, C, D, E and F.

A	B	C	D	E	F
C₂H₄	C₂H₆	C₃H₆	C₃H₈	C₄H₈	C₄H₁₀

(a)(i)

Explain which homologous series compound B belongs to.

[2]

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(a)(ii)

Give the letter of the compound that has the same empirical formula as its molecular formula.

[1]

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(a)(iii)

Compound F exists as two isomers.

Explain what is meant by the term isomers.

Include the structures of the two isomers of compound F in your answer.

[3]

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(b)

Describe how compound D can be obtained from crude oil using the industrial process of fractional distillation.

[4]

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(c)

Compound C can be used to make a polymer.

(c)(i)

State the type of polymer formed from compound C.

[1]

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(c)(ii)

Name the polymer formed from compound C.

[1]

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(c)(iii)

Draw the structure of this polymer.

Include the displayed formula of the repeat unit.

[2]

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Chemistry Paper 1 January 2020, Question 5 14 marks

Also involves Naming organic compounds

The boxes show the displayed formulae of six organic compounds, P, Q, R, S, T and U.

(a)

Use the letters P, Q, R, S, T and U to answer these questions.

Each letter may be used once, more than once or not at all.

(a)(i)

Give the letter of the compound that is not a hydrocarbon.

[1]

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(a)(ii)

Give the letters of the two compounds that have the same empirical formula.

[1]

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(a)(iii)

Give the letter of the compound that is used to manufacture poly(propene).

[1]

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(b)

Describe a test that can be used to distinguish between compounds Q and T.

result with compound Q_........

result with compound T_........

[3]

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(c)

Compounds P, Q and R are members of the same homologous series.

Give two characteristics of a homologous series.

[2]

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(d)

This is the displayed formula of an alkene, V.

(d)(i)

Give the name of alkene V.

[1]

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(d)(ii)

Draw the displayed formula of another alkene that is an isomer of alkene V.

[1]

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(e)

An organic compound has the percentage composition by mass

C = 36.36% H = 6.06% F = 57.58%

(e)(i)

Show that the empirical formula of the compound is CH₂F

[2]

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(e)(ii)

The relative molecular mass (M_r) of the compound is 66.

Determine the molecular formula of the compound.

[2]

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