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Practice · Chemistry · 2025 syllabus · R3.4

IB Chemistry R3.4 Electron-pair sharing reactions: practice questions

10 exam-style questions on R3.4 Electron-pair sharing reactions, SL and HL, 10 marked HL: 6 multiple choice and 4 structured. Each one comes with the mark scheme, a model answer and the reasoning behind every mark. Free with your email.

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R3.4-01 · Paper 1A style · multiple choice · 1 mark · HL

Role of ammonia in substitution

What is the role of ammonia in this reaction?
CH3CH2Br + NH3 → CH3CH2NH2 + HBr [1]

  1. Electrophile and Lewis acid
  2. Nucleophile and Lewis acid
  3. Electrophile and Lewis base
  4. Nucleophile and Lewis base
Show the answer and the reasoning

Answer: D. D is correct. The lone pair on nitrogen attacks the carbon bonded to bromine, forming a new bond: ammonia is a nucleophile, and because it donates an electron pair it is also a Lewis base. A and C: an electrophile accepts an electron pair. B: a Lewis acid accepts an electron pair.

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The 10 questions in R3.4

  1. R3.4-01 Role of ammonia in substitutionPaper 1A style · multiple choice · 1 mark · HL
  2. R3.4-02 The electrophile that attacks benzenePaper 1A style · multiple choice · 1 mark · HL
  3. R3.4-03 Major product from HBrPaper 1A style · multiple choice · 1 mark · HL
  4. R3.4-04 Fastest halogenoalkanePaper 1A style · multiple choice · 1 mark · HL
  5. R3.4-05 Features of SN1Paper 1A style · multiple choice · 1 mark · HL
  6. R3.4-06 Which are Lewis acidsPaper 1A style · multiple choice · 1 mark · HL
  7. R3.4-07 An SN2 mechanism with curly arrowsPaper 2 style · structured question · 7 marks · HL
  8. R3.4-08 Adding HBr to propenePaper 2 style · structured question · 6 marks · HL
  9. R3.4-09 Telling SN1 from SN2Paper 2 style · structured question · 5 marks · HL
  10. R3.4-10 Why benzene substitutesPaper 2 style · structured question · 5 marks · HL

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Every Biology and Chemistry question here is original, written for practice in the style of the papers set since the 2025 syllabus, with invented data. Developed independently from the International Baccalaureate Organization, which has not endorsed it. Found a mistake? Email vytis@limeadmissions.com with the question id.