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Home Revision AQA A-Level Chemistry Past-paper questions Halogenoalkanes

AQA 7404/7405 · Real past-paper questions · AQA’s mark schemes

Halogenoalkanes: AQA A-Level Chemistry past-paper questions

27 questions, 116 marks (25 AS, 2 A-level only), from 2017–2025. Each has AQA’s mark scheme a tap away. Free, no sign-up.

Joe White · AQA AS & A-Level Chemistry (7404/7405) · Not affiliated with or endorsed by AQA

How AQA examines halogenoalkanes

27 questions, 17 multiple choice. The written parts are most often 2 marks, and “Give”, “State” and “Name” lead: the name of a mechanism, a reagent and its conditions, or an IUPAC name.

When a mechanism is asked for (“Outline”, 5 times), the marks are for the curly arrows: from a lone pair or a bond, to an atom or a bond, with the C–halogen bond breaking. Know which conditions favour substitution and which favour elimination, and why the carbon–halogen bond enthalpy sets how fast each halogenoalkane reacts. Four of these questions also draw on alkanes.

Multiple choice (17)

Q1[1 mark]

June 2025 · Paper 3 · Q10

Which diagram shows a correct step in the mechanism for an elimination reaction of bromoethane?

  1. C C H H H H H Br − OH
  2. C C H H H H H Br − OH
  3. C C H H H H H Br − OH
  4. C C H H H H H Br − OH

Q2[1 mark]

June 2025 · Paper 3 · Q8

Each of the conversions shown uses KOH as a reactant.

In which conversion does KOH not act as a base?

  1. (CH3)2NH2+Br− to (CH3)2NH
  2. CH3COOH to CH3COO−K+
  3. CH3CH2Br to H2C=CH2
  4. CH3Br to CH3OH

Q3[1 mark]

June 2024 · AS Paper 2 · Q12

A halogenoalkane reacts with ethanolic potassium hydroxide to form these alkenes by elimination: • 2-ethylpent-1-ene • E-3-methylhex-2-ene • Z-3-methylhex-2-ene • E-3-methylhex-3-ene • Z-3-methylhex-3-ene Which halogenoalkane would form these alkenes in this reaction?

  1. 1-bromo-2-ethylpentane
  2. 2-bromo-3-methylhexane
  3. 3-bromo-3-methylhexane
  4. 3-bromo-4-methylhexane

Q4[1 mark]

June 2023 · Paper 3 · Q30

Most scientists believe that the concentration of ozone in the upper atmosphere should not be allowed to decrease. Which statement is a correct reason for this belief?

  1. Ozone helps to prevent global warming.
  2. Ozone is an efficient disinfectant.
  3. Ozone helps to remove pollutants such as chloroalkanes.
  4. Ozone absorbs ultraviolet radiation.

Q5[1 mark]

June 2023 · AS Paper 2 · Q12

Most scientists believe that ozone in the upper atmosphere should not be allowed to become depleted. Which is a valid reason for this belief?

  1. Ozone absorbs ultraviolet radiation.
  2. Ozone helps to prevent global warming.
  3. Ozone helps to remove pollutants such as chloroalkanes.
  4. Ozone is an efficient disinfectant.

Q6[1 mark]

June 2022 · Paper 3 · Q23

Which compound is formed from bromoethane in a nucleophilic substitution reaction?

  1. CH3CN
  2. CH3CH2NH2
  3. CH2=CH2
  4. CH3CH2OSO2OH

Q7[1 mark]

June 2022 · AS Paper 2 · Q22

When 2-bromobutane is warmed with potassium hydroxide solution, substitution and elimination reactions both occur. What is the role of the hydroxide ions in the elimination reaction?

  1. base
  2. catalyst
  3. electrophile
  4. nucleophile

Q8[1 mark]

June 2022 · AS Paper 2 · Q21

When 2-bromobutane is warmed with potassium hydroxide solution, substitution and elimination reactions both occur. Which of these compounds is not produced?

  1. butan-1-ol
  2. butan-2-ol
  3. but-1-ene
  4. E-but-2-ene

Q9[1 mark]

November 2021 · AS Paper 2 · Q13

Which compound is not formed by reacting 3-bromo-3-methylhexane with warm, ethanolic potassium hydroxide?

  1. 2-ethylpent-1-ene
  2. 3-methylhex-1-ene
  3. 3-methylhex-2-ene
  4. 3-methylhex-3-ene

Q10[1 mark]

November 2021 · AS Paper 2 · Q16

The question below refers to the reaction of 1-bromopropane with a solution of potassium cyanide in aqueous ethanol. The reactions of 1-bromopropane and 1-chloropropane with potassium cyanide in aqueous ethanol occur at different rates under the same conditions. Which row correctly shows the compound that has a faster rate of reaction and the correct reason for this? Compound Reason

  1. 1-bromopropane C–Br bond weaker than C–Cl bond
  2. 1-bromopropane C–Br bond stronger than C–Cl bond
  3. 1-chloropropane C–Br bond weaker than C–Cl bond
  4. 1-chloropropane C–Br bond stronger than C–Cl bond

Q11[1 mark]

November 2021 · AS Paper 2 · Q14

The question below refers to the reaction of 1-bromopropane with a solution of potassium cyanide in aqueous ethanol. What is the organic product of this reaction?

  1. propylamine
  2. butylamine
  3. propanenitrile
  4. butanenitrile

Q12[1 mark]

November 2020 · AS Paper 2 · Q10

Which statement is not correct about ozone?

  1. It absorbs harmful ultraviolet radiation in the upper atmosphere.
  2. Its decomposition is catalysed by chlorine molecules.
  3. It decomposes to form oxygen.
  4. Ozone holes are regions of the upper atmosphere where there is a reduced concentration of ozone.

Q13[1 mark]

June 2019 · AS Paper 2 · Q16

Which compound can react with ammonia to produce propylamine?

  1. CH3CH═CH2
  2. CH3CH2CH2OH
  3. CH3CH2CH2Br
  4. CH3CH2CH3

Q14[1 mark]

June 2019 · AS Paper 2 · Q19

Which species can act as a nucleophile?

  1. NH4+
  2. CH3OH
  3. CH4
  4. H+

Q15[1 mark]

June 2019 · AS Paper 2 · Q22

Which compound could not be produced by reacting 2-bromo-3-methylbutane with sodium hydroxide?

  1. 2-methylbut-1-ene
  2. 3-methylbut-1-ene
  3. 2-methylbut-2-ene
  4. 3-methylbutan-2-ol

Q16[1 mark]

June 2018 · AS Paper 2 · Q18

Which species could act as a nucleophile?

  1. BH3
  2. NH4+
  3. PH3
  4. SiH4

Q17[1 mark]

June 2017 · AS Paper 2 · Q16

Which compound has the fastest rate of reaction with potassium cyanide to form pentanenitrile?

  1. 1-bromobutane
  2. 1-chlorobutane
  3. 1-fluorobutane
  4. 1-iodobutane

Structured questions (10)

Q18[14 marks]

June 2025 · AS Paper 2 · Q1

This question is about halogenoalkanes.

01.1 Halogenoalkanes undergo substitution reactions with nucleophiles such as

CN−, NH3 and OH−

Explain why halogenoalkanes react with nucleophiles.

2 marks

01.2 2-Bromobutane reacts with ammonia to form CH3CH(NH2)CH2CH3

Complete the mechanism for this reaction.

2-Bromobutane reacts with KOH to give a mixture of products.

3 marks

01.3 Identify the solvent that should be used to ensure that butan-2-ol is the main organic product when 2-brombutane reacts with KOH

1 mark

01.4 Under different conditions, 2-bromobutane reacts with KOH to form but-1-ene and two other alkenes.

Name and complete the mechanism to form but-1-ene from 2-bromobutane.

Identify the other two alkenes formed.

Name of mechanism

Mechanism

Other alkene 1

Other alkene 2

5 marks

01.5 The carbocation (CH3)3C+ is formed as an intermediate in the reaction of

2-bromo-2-methylpropane with KCN

Suggest the value of the bond angle around the central C atom in the

(CH3)3C+ carbocation.

1 mark

01.6 A co-ordinate bond is formed when the (CH3)3C+ carbocation reacts with CN− to form a nitrile.

Explain how this co-ordinate bond is formed during this reaction.

2 marks

Q19[12 marks]

June 2025 · Paper 2 · Q1

This question is about different ways to make 1,2-dichlorobutane.

Cl Cl Cl Reaction 1 Reaction 2 Reaction 3

01.1 Give the name of the mechanism for reaction 1.

State one essential condition needed for reaction 1.

Name of mechanism

Essential condition

2 marks

01.2 Give equations to show three essential steps in the mechanism for reaction 1.

3 marks

01.3 Suggest two reasons why using reaction 1 is likely to give a low yield of

1,2-dichlorobutane.

Reason 1

Reason 2

2 marks

01.4 Give a suitable reagent and conditions needed for reaction 2.

Reagent

Conditions

2 marks

01.5 Identify the reagent and name the mechanism for reaction 3.

Reagent

Name of mechanism

2 marks

01.6 Use of the reagent for reaction 2 followed by the reagent for reaction 3 gives another organic product.

Give the structure of the other organic product.

1 mark

Q20[7 marks]

June 2024 · AS Paper 2 · Q3

This question is about CFCl3

CFCl3 used to be the propellant in most aerosol cans.

(a) Use IUPAC rules to name CFCl3

1 mark

(b) Give an equation for each of the two propagation steps in the conversion of CHFCl2 into CFCl3

Equation 1

Equation 2

2 marks

(c) In the presence of ultraviolet radiation, CFCl3 breaks down in the upper atmosphere to form chlorine free radicals.

Give an equation for this reaction.

1 mark

(d) Chlorine free radicals catalyse the decomposition of ozone.

Give two equations to show how chlorine free radicals decompose ozone.

Equation 1

Equation 2

2 marks

(e) The production and use of CFCs have been banned in many countries because they decrease the amount of ozone in the upper atmosphere.

State why ozone in the upper atmosphere is important for life on Earth.

1 mark

Q21[4 marks]

June 2023 · AS Paper 2 · Q3

This question is about reactions of halogenoalkanes with hydroxide ions.

(a) Outline the mechanism for the nucleophilic substitution reaction of 1-bromobutane with sodium hydroxide.

2 marks

A student investigated the rate of nucleophilic substitution of halogenoalkanes with hydroxide ions.

Identical concentrations of 1-bromobutane and 1-iodobutane were reacted separately with sodium hydroxide solution under the same conditions.

The concentration of halide ions was monitored during each experiment.

The graph below shows the student’s results.

0.12 0.10 0.08 0.06 0.04 0.02 0.00 0 100 200 300 400 500 600 Time / s Concentration of halide ions / mol dm −3 Key Reaction with 1-iodobutane Reaction with 1-bromobutane

(b) State how the graph shows that the rate of reaction of 1-iodobutane is faster than the rate of reaction of 1-bromobutane.

State why the rates are different.

2 marks

Q22[9 marks]

June 2022 · AS Paper 2 · Q5

This question is about the synthesis of propylamine (CH3CH2CH2NH2) by the reaction of 1-iodopropane (CH3CH2CH2I) with an excess of ammonia.

CH3CH2CH2I + 2 NH3 → CH3CH2CH2NH2 + NH4I

(a) Name and outline the mechanism for this reaction.

Name of mechanism

Outline of mechanism

5 marks

(b) 1-iodopropane is a liquid at room temperature.

Calculate the number of molecules in 5.0 cm3 of 1-iodopropane (Mr = 169.9). Give your answer in standard form.

For 1-iodopropane, density = 1.75 g cm−3

The Avogadro constant, L = 6.022 x 1023 mol−1

Number of molecules

2 marks

(c) In an experiment, 10.3 g of 1-iodopropane (Mr = 169.9) are reacted with an excess of ammonia. 2.3 g of propylamine (Mr = 59.0) are produced.

Calculate the percentage yield in this experiment.

Percentage yield

2 marks

Q23A2[15 marks]

June 2022 · Paper 3 · Q3

Under suitable conditions, 2-bromobutane reacts with sodium hydroxide to produce a mixture of five products, A, B, C, D and E.

Products A, B and C are alkenes.

A is a structural isomer of B and C.

A does not exhibit stereoisomerism.

B and C are a pair of stereoisomers.

Products D and E are alcohols.

D and E are a pair of enantiomers.

(a) Give the names of the two concurrent mechanisms responsible for the formation of the alkenes and the alcohols.

Mechanism to form alkenes

Mechanism to form alcohols

2 marks

(b) Define the term stereoisomers.

2 marks

(c) Deduce the name of isomer A.

Explain why A does not exhibit stereoisomerism.

Name

Explanation

2 marks

(d) Outline the mechanism for the reaction of 2-bromobutane with sodium hydroxide to form alkene A.

3 marks

(e) Deduce the name of isomer B and the name of isomer C.

Explain the origin of the stereoisomerism in B and C.

Name

Explanation

2 marks

(f) Draw 3D representations of enantiomers D and E to show how their structures are related.

2 marks

(g) A student compares the rates of hydrolysis of 1-chlorobutane, 1-bromobutane and 1-iodobutane.

The suggested method is:

  • add equal volumes of the three halogenoalkanes to separate test tubes
  • add equal volumes of aqueous silver nitrate to each test tube
  • record the time taken for a precipitate to appear in each test tube.

State and explain the order in which precipitates appear.

Order in which precipitates appear

Explanation

2 marks

Q24[7 marks]

November 2021 · Paper 2 · Q9

This question is about the ozone layer in the upper atmosphere.

(a) State why the ozone layer is beneficial for living organisms.

1 mark

(b) State how chlorofluorocarbons (CFCs) form chlorine atoms in the upper atmosphere.

1 mark

(c) Give equations to show how chlorine atoms catalyse the decomposition of ozone.

2 marks

(d) Hydrochlorofluorocarbons (HCFCs) have been used in place of CFCs.

In the mechanism to make an HCFC from a fluoroalkane, two incomplete steps are shown.

Complete each step in the mechanism.

Give the name of the type of step shown by both these equations.

→ • CHF2 + HCl

  • CHF2 + Cl2 →

Type of step

3 marks

Q25[8 marks]

November 2021 · AS Paper 2 · Q4

CFCs were used as refrigerants and in aerosols.

The scientists Rowland and Molina published research in 1974 to show that CFCs are responsible for the destruction of ozone molecules in the upper atmosphere.

A few years later, other scientists discovered that the concentration of ozone in the upper atmosphere was decreasing.

In 1987 there was an agreement by many countries to restrict the use of CFCs.

(a) The molecule CFC-11 was commonly used as a refrigerant.

Cl F C Cl Cl

Use IUPAC rules to name CFC-11

1 mark

(b) A molecule of CFC-11 breaks down in the upper atmosphere to form a chlorine free radical.

Give the equation for this reaction.

1 mark

(c) A typical refrigerator contained 0.50 kg of CFC-11 (Mr = 137.5).

One molecule of CFC-11 causes the destruction of approximately 100 000 molecules of ozone.

Use these data to estimate the number of molecules of ozone that can be destroyed by 0.50 kg of CFC-11

Give your answer in standard form.

The Avogadro constant, L = 6.022 × 1023 mol−1

Number of molecules of ozone

2 marks

(d) State the benefit to life on Earth of ozone in the upper atmosphere.

1 mark

(e) Suggest one reason why the use of CFCs was not restricted until several years after Rowland and Molina published their research.

1 mark

(f) CFC-11 is a greenhouse gas that can contribute to global warming.

State and explain how CFC-11 is able to contribute to global warming.

2 marks

Q26[14 marks]

November 2020 · AS Paper 2 · Q1

This question is about 1-chloropropane.

(a) Define the term standard enthalpy of formation.

2 marks

(b) The equation for a reaction used to manufacture 1-chloropropane is

3 CH3CH2CH2OH(l) + PCl3(l) → 3 CH3CH2CH2Cl(l) + H3PO3(s)

The enthalpy change for this reaction, ΔH, is –114 kJ mol−1

The table contains some standard enthalpy of formation data.

SubstancePCl3(l)CH3CH2CH2Cl(l)H3PO3(s)
ΔfH⦵ / kJ mol−1–339–130–972

Calculate a value for the standard enthalpy of formation of propan-1-ol using the enthalpy change for the reaction and data from the table.

Standard enthalpy of formation kJ mol−1

3 marks

(c) 1-chloropropane can also be produced by the reaction between propane and chlorine in the presence of ultraviolet light.

State why ultraviolet light is needed for this reaction to occur.

Give an equation for each propagation step in the formation of 1-chloropropane from propane.

Why ultraviolet light is needed

Propagation step 1

Propagation step 2

3 marks

(d) The C–Cl bond in 1-chloropropane is polar because carbon and chlorine have different electronegativities.

Define the term electronegativity.

1 mark

(e) Ammonia reacts with 1-chloropropane to form propylamine.

Name and outline the mechanism for this reaction.

Name of mechanism

Outline of mechanism

5 marks

Q27A2[9 marks]

November 2020 · Paper 2 · Q5

This question is about 2-bromopropane.

(a) Define the term electronegativity.

Explain the polarity of the C–Br bond in 2-bromopropane.

Electronegativity

Explanation

3 marks

(b) Outline the mechanism for the reaction of 2-bromopropane with an excess of ammonia.

4 marks

(c) Draw the skeletal formula of the main organic species formed in the reaction between a large excess of 2-bromopropane and ammonia.

Give a use for the organic product.

Skeletal formula

Use

2 marks

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