Edexcel A-Level Chemistry AS Paper 2, June 2019: Question 2

10 marks · Medium difficulty · Short Open Response

Describe characteristics of a homologous series, identify reaction reagents and mechanisms for alkenes and halogenoalkanes, and draw and name structural isomers.

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Question

An exam question about organic compounds containing parts (a) on homologous series and propene, (b) on the conversion of propene to 1-chloropropane and 2-chloropropane via electrophilic addition, and (c) on the conversion of chloropropanes to nitriles and drawing structural isomers.
Question text

2 This question is about organic compounds.

(a) Organic compounds can be grouped together in homologous series.

(i) Describe two characteristics of a homologous series.

(2)

(ii) Name the homologous series to which propene belongs.

(1)

(b) Propene can be converted into a mixture of 1-chloropropane and

2-chloropropane, in which 2-chloropropane is the major product.

(i) Give the reagent required for this reaction.

(1)

(ii) What is the type and mechanism of the reaction in (b)(i)?

(1)

A electrophilic addition

B nucleophilic addition

C electrophilic substitution

D nucleophilic substitution

(c) 1-chloropropane and 2-chloropropane can be converted into compounds

containing the nitrile functional group.

(i) Under appropriate conditions, 1-chloropropane can be converted into

butanenitrile, CH3CH2CH2CN.

Which is the reagent for this conversion?

(1)

A ammonia

B nitric acid

4 C potassium cyanide

D silver nitrate *P55611A0428*

(ii) Under appropriate conditions, 2-chloropropane can be converted into a

structural isomer of butanenitrile.

State what is meant by the term ‘structural isomer’.

(2)

(iii) Give the displayed formula and systematic name of the isomer of

butanenitrile formed in (c)(ii). You must show all the bonds.

(2)

Displayed formula

Name

(Total for Question 2 = 10 marks)

Mark scheme

Show the mark scheme The official mark scheme showing acceptable answers, incorrect distractors, and guidance for all parts of question 2.

How to answer it

Organic Compounds Study Guide

What this question tests

This question assesses foundational organic chemistry concepts including homologous series definitions, classification of reaction mechanisms (electrophilic addition), nucleophilic substitution reagents, structural isomerism definitions, and drawing precise displayed formulas with systematic IUPAC naming.

Question 2(a)

Homologous Series and Functional Groups

✅ Correct Answers

  • Part (i): Any two of: same general formula, neighbouring compounds differ by a -CH₂- group, same functional group / similar chemical properties, gradual change/trend in physical properties. (2 marks)
  • Part (ii): Alkene(s). (1 mark)

💡 Key Knowledge

  • A homologous series shares chemical characteristics because members possess the same functional group.
  • Propene contains a carbon-carbon double bond ( C=C ), classifying it as an alkene.

❌ Common Errors

  • Stating they have the same "molecular formula" or "structural formula" instead of general formula.
  • Writing "alkanes" instead of "alkenes" for part (ii).

🧠 Exam Technique

  • When asked for characteristics of a homologous series, bullet points ensure you state distinct, non-contradictory chemical facts clearly.
Total for 2(a): 3 Marks
Question 2(b)

Halogenoalkane Formation and Mechanisms

✅ Correct Answers

  • Part (i): Hydrogen chloride / HCl(g) / H-Cl . (1 mark)
  • Part (ii): A (electrophilic addition). (1 mark)

💡 Key Knowledge

  • Alkenes react with hydrogen halides via electrophilic addition across the C=C double bond.
  • State symbols or chemical formulas like HCl are fully acceptable, but avoid ambiguous terms like "hydrochloric acid" since water is absent.

❌ Common Errors

  • Writing HCl(aq) , which introduces water and is penalized because anhydrous conditions or pure gas is required for direct addition to alkenes here.
Total for 2(b): 2 Marks
Question 2(c)

Nitrile Synthesis, Isomerism, and Displayed Formulas

✅ Correct Answers

  • Part (i): C (potassium cyanide). (1 mark)
  • Part (ii): Same molecular formula ( C₄H₇N ) but different structural / displayed formula. (2 marks)
  • Part (iii): Displayed formula showing every single covalent bond explicitly, including all C-H bonds and the C≡N triple bond; Name: (2-)methyl(-1-)propan(e)nitrile . (2 marks)

💡 Key Knowledge

  • Halogenoalkanes react with ethanolic potassium cyanide ( KCN ) under reflux to form nitriles, lengthening the carbon chain.
  • Structural isomers share the exact molecular formula but feature different atom connectivity.

❌ Common Errors

  • Failing to show all bonds explicitly in the displayed formula (e.g., condensing -CH₃ or writing -CN without showing the C≡N triple bond).
  • Stating isomers have the "same general formula" instead of "same molecular formula".

🧠 Exam Technique

  • Always double-check the instruction "You must show all the bonds" — shorthand groups like -CH₃ will lose you marks on displayed formula questions!
Total for 2(c): 5 Marks

Topics

Organic Chemistry · Topic 6: Organic Chemistry I

Question and mark scheme from the Edexcel A-Level Chemistry examination, AS Paper 2, June 2019. QuestionVault is an independent revision resource; questions remain the copyright of the awarding body.