Edexcel A-Level Chemistry Paper 3, November 2020: Question 9

9 marks · Medium difficulty · Open Response

Compare and contrast the preparation and basicity of phenylamine and butylamine, write the equation for the formation of an amide from propanoyl chloride and pentylamine, and identify the amine monomer from a given polyamide structure.

Practise this question

Question

A 4-part exam question about amines. Part (a) shows chemical structures and equations for the preparation of phenylamine from nitrobenzene and butylamine from butanenitrile, asking to compare and contrast the preparations (3 marks). Part (b) asks to compare and contrast the basicity of phenylamine and butylamine (3 marks). Part (c) asks for the equation and name of the amide formed from the reaction between propanoyl chloride and pentylamine (2 marks). Part (d) shows the structural formula of a section of a polyamide and asks to identify the amine monomer that reacts to form it (1 mark).
Question text

9 This question is about amines.

(a) Phenylamine is an aromatic amine and butylamine is an aliphatic amine.

Phenylamine can be prepared from nitrobenzene.

NO2 NH2

Butylamine can be prepared from butanenitrile.

C3H7CN → C4H9NH2

Compare and contrast these two preparations of amines.

(3)

(b) Compare and contrast the basicity of phenylamine and butylamine.

(3)

… 26

… *P62670A02632*

(c) Write the equation for the reaction between propanoyl chloride and pentylamine.

Include the name of the amide formed.

State symbols are not required.

(2)

Name of amide …

(d) A section of a polyamide is shown.

O H

N

N

O H

Identify, by name or formula, the amine monomer that reacts to form this

polyamide. 27

*P62670A02732* (1)

(Total for Question 9 = 9 marks)

Mark scheme

Show the mark scheme The mark scheme provides detailed guidance for answering all four parts. Part (a) awards marks for recognizing both are reduction reactions, and specifying the correct reagents (tin and conc. HCl for phenylamine; H2/Ni or LiAlH4 for butylamine). Part (b) awards marks for stating both have a lone pair to accept protons, explaining that in phenylamine the lone pair is delocalized into the ring making it a weaker base, and that the alkyl group in butylamine is electron-releasing making it a stronger base. Part (c) lists the balanced chemical equation (C2H5COCl + C5H11NH2 -> C2H5CONHC5H11 + HCl) and the name N-pentylpropanamide. Part (d) accepts the formula H2N(CH2)6NH2 or the name 1,6-diaminohexane.

How to answer it

Edexcel A-Level Chemistry: Amines Exam Guide

What this question tests

This question assesses your knowledge of amine chemistry across several key areas: synthetic routes for preparing aromatic vs. aliphatic amines, comparative basicity based on electronic effects (inductive effects vs. delocalisation), nucleophilic addition-elimination reactions between acyl chlorides and primary amines to form secondary amides, and deducing monomers from condensation polymer structures (polyamides).

Question 9(a) - Amine Preparation

Compare and contrast the preparations of phenylamine and butylamine

✅ Correct Answer / Mark Scheme

  • Similarity (1 mark): Both are reduction reactions.
  • Difference 1 (1 mark): Phenylamine is prepared using tin (Sn) and concentrated hydrochloric acid (HCl).
  • Difference 2 (1 mark): Butylamine is prepared using either hydrogen gas with a nickel catalyst OR lithium tetrahydridoaluminate(III) (LiAlH₄) in dry ether.

❌ Common Errors

  • Saying both simply "require hydrogen" without specifying the correct reagents/conditions.
  • Using dilute hydrochloric acid or sulfuric acid instead of concentrated HCl for the reduction of nitrobenzene.
Examiner Insight: To score full marks here, candidates must clearly state one structural/reaction similarity and explicitly contrast the different reagents required for the aromatic versus aliphatic pathways.
Question 9(b) - Basicity of Amines

Compare and contrast the basicity of phenylamine and butylamine

✅ Correct Answer / Mark Scheme

  • Similarity (1 mark): Both are basic because they have a lone pair of electrons on the nitrogen atom which can accept a proton (H⁺).
  • Difference 1 (1 mark): In phenylamine, the nitrogen lone pair overlaps with the delocalised pi-system of the benzene ring, making it less available to accept a proton (weaker base).
  • Difference 2 (1 mark): In butylamine, the alkyl group (butyl) is electron-releasing via a positive inductive effect, increasing electron density on nitrogen and making the lone pair more available (stronger base).

🧠 Exam Technique

Structure your answer clearly: start with why both function as bases (proton acceptors via nitrogen's lone pair), then explain the delocalisation effect in the aromatic ring, and finish with the positive inductive effect of the alkyl chain.

Examiner Insight: Top-level responses explicitly linked the availability of the lone pair of electrons on the nitrogen atom to the specific electronic effects operating in each molecule.
Question 9(c) - Acylation & Amide Formation

Reaction between propanoyl chloride and pentylamine

✅ Correct Answer / Mark Scheme

Equation: C₂H₅COCl + C₅H₁₁NH₂ → C₂H₅CONHC₅H₁₁ + HCl

Name of Amide: N-pentylpropanamide

❌ Common Errors

  • Writing molecular formulae instead of structural/displayed formulae where required, or misspelling the amide name as "N-pentylpropylamine".
  • Omitting the by-product HCl from the stoichiometric equation.
Examiner Insight: Ensure organic products are named systematically using IUPAC conventions. Acyl chlorides react with primary amines to form secondary amides alongside hydrogen chloride gas.
Question 9(d) - Polyamide Monomers

Identify the amine monomer that reacts to form the given polyamide

✅ Correct Answer / Mark Scheme

Name: 1,6-diaminohexane

Formula: H₂N(CH₂)₆NH₂ (or equivalent structural/skeletal representation)

💡 Key Knowledge

Polyamides are formed via condensation polymerisation between a dicarboxylic acid (or acyl chloride) and a diamine. Look at the section of the chain adjacent to the peptide/amide link -CO-NH- containing the nitrogen atom to count the carbon chain length of the amine monomer.

Examiner Insight: Molecular formulae (such as H₂NC₆H₁₂NH₂ ) were not accepted unless standard structural clarity was shown. Providing both correct name and correct formula guarantees the mark if consistent.

Topics

Organic Chemistry · Topic 18: Organic Chemistry III

Question and mark scheme from the Edexcel A-Level Chemistry examination, Paper 3, November 2020. QuestionVault is an independent revision resource; questions remain the copyright of the awarding body.