AQA A-Level Chemistry Paper 2, 2022: Question 10

10 marks · Hard difficulty · State/Explain/Describe

Reaction Scheme Analysis This question involves a multi-step reaction scheme, focusing on the formation of amines and derivatives. It requires identifying reagents for nitration (step 1) and reduction (step 2), naming the mechanism for acylation (step 3), and detailing the conditions for the formation of chloromethylbenzene (step 4). Further questions address differences in yields between amines A and B and the relative basicity of amine B compared to amine A.

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Question

AQA A-Level Chemistry Paper 2, 2022: Question 10
Question text

10 This question is about the reaction scheme shown.

10.1 State the reagents needed for step 1 and the reagents needed for step 2.

[3 marks]

step 1

step 2

10.2 Give the name of the mechanism for the reaction in step 3.

[1 mark]

10.3 Name the reagent for step 4.

State a necessary condition for step 4.

[2 marks]

Reagent

Condition

10.4 Amine A is formed in step 2 and amine B is formed in step 5.

*28* Explain why the yield of B in step 5 is less than the yield of A in step 2.

[2 marks]

10.5 Explain why amine B is a stronger base than amine A.

[2 marks]

Mark scheme

Show the mark scheme Mark scheme for AQA A-Level Chemistry Paper 2, 2022: Question 10

Question Answers Additional Comments/Guidelines Mark

Step 1 Conc HNO3 M1

Step 1 Conc H2SO4 If conc missing in both allow 1 for HNO3 and H2SO4 M2

10.1

Step 2 Sn and HCl Allow Fe and HCl or Ni and H2 M3

(3 x AO1)

(nucleophilic) addition-elimination 1

10.2

(AO1)

Chlorine Allow Cl2 M1

10.3 UV (light) Allow sunlight / High temp (above 300oc)

M2

(2 x AO1)

In Step 5 further substitution / gives other amine products 1

10.4

In Step 2 only one amine 1

(2 x AO3)

In B Alkyl group is electron donating or positive inductive effect Or in A lone pair (on N partially) delocalised 1

10.5

Lone pair on N more available Lone pair on N less available 1

(2 x AO2)

How to answer it

Study Guide: Reaction Scheme Analysis

Part (a)

What to do: Identify the reagents for step 1 (nitration of methylbenzene) and step 2 (reduction of nitro group).

  • Step 1: Concentrated HNO3 and H2SO4
  • Step 2: Sn and HCl or Fe and HCl

Common errors:

  • Failing to mention the concentrated forms of the acids in step 1.
  • Not specifying Sn or Fe for reduction in step 2.
Teacher Tip: Emphasise that nitration requires concentrated acids and that Sn/Fe is the catalyst for reduction, producing the amine.

Part (b)

What to do: Name the mechanism for step 3.

Nucleophilic addition-elimination

Common errors:

  • Confusing with "electrophilic substitution."
  • Forgetting the "elimination" part of the mechanism name.
Teacher Tip: Break down the mechanism into its two stages to help students remember the full name.

Part (c)

What to do: Provide the reagent and condition for step 4 (chlorination of methylbenzene).

  • Reagent: Chlorine (Cl2)
  • Condition: UV light

Common errors:

  • Not specifying UV light as the condition.
  • Omitting the reagent or writing "HCl" instead.
Teacher Tip: Highlight that UV light is required to generate radicals for this free radical substitution.

Part (d)

What to do: Explain why the yield of amine B (step 5) is less than the yield of amine A (step 2).

Correct Answer: In step 5, amine B undergoes further substitution to form other products, reducing its yield. In step 2, amine A is the only organic product.

Common errors:

  • Failing to mention further substitution in step 5.
  • Assuming experimental errors rather than chemical reasoning.
Teacher Tip: Discuss why alkylamines are more reactive and prone to further substitution reactions.

Part (e)

What to do: Explain why amine B is a stronger base than amine A.

Correct Answer: Amine B has an alkyl group, which is electron-donating, increasing the availability of the lone pair on nitrogen. In amine A, the lone pair is partially delocalised into the benzene ring, making it less available for protonation.

Common errors:

  • Not referring to the inductive effect of the alkyl group.
  • Failing to mention delocalisation in the aromatic ring.
Common Misconception: Some students think amines in benzene rings are always stronger bases due to resonance, without recognising that delocalisation reduces the lone pair's availability.

Topics

Organic Chemistry · 3.3.11 Amines · 3.3.14 Organic Synthesis · 3.3.10 Aromatic Chemistry

Question and mark scheme from the AQA A-Level Chemistry examination, Paper 2, 2022. QuestionVault is an independent revision resource; questions remain the copyright of the awarding body.