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Practice · Chemistry · 2025 syllabus · R2.1

IB Chemistry R2.1 How much? The amount of chemical change: practice questions

9 exam-style questions on R2.1 How much? The amount of chemical change, SL and HL: 5 multiple choice, 2 data-based and 2 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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R2.1-01 · Paper 1A style · multiple choice · 1 mark

Atom economy of fermentation

Ethanol is made by fermenting glucose: C6H12O6 → 2C2H5OH + 2CO2. M(C6H12O6) = 180.18 g mol−1 and M(C2H5OH) = 46.08 g mol−1. What is the atom economy for making ethanol? [1]

  1. 25.6 %
  2. 48.9 %
  3. 51.1 %
  4. 104.7 %
Show the answer and the reasoning

Answer: C. C is correct. Atom economy = mass of desired product ÷ total mass of reactants × 100 = (2 × 46.08) ÷ 180.18 × 100 = 51.1 %. A counts only one ethanol. B is the share that ends up as CO2. D divides by the mass of the other product instead of the reactants; an atom economy above 100 % is impossible.

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The 9 questions in R2.1

  1. R2.1-01 Atom economy of fermentationPaper 1A style · multiple choice · 1 mark
  2. R2.1-02 Gas volumes after combustionPaper 1A style · multiple choice · 1 mark
  3. R2.1-03 Limiting reactant and yieldPaper 1A style · multiple choice · 1 mark
  4. R2.1-04 Oxygen needed from a massPaper 1A style · multiple choice · 1 mark
  5. R2.1-05 Percentage yield of limePaper 1A style · multiple choice · 1 mark
  6. R2.1-06 Yield of an oxidation by titrationPaper 1B style · data-based · 7 marks
  7. R2.1-07 Carbon dioxide lost by massPaper 1B style · data-based · 7 marks
  8. R2.1-08 Atom economy and yield of an esterPaper 2 style · structured question · 5 marks
  9. R2.1-09 Mass of a precipitatePaper 2 style · structured question · 4 marks

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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.