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Practice · Chemistry · 2025 syllabus · S1.4

IB Chemistry S1.4 Counting particles by mass: the mole: practice questions

8 exam-style questions on S1.4 Counting particles by mass: the mole, SL and HL: 4 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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S1.4-01 · Paper 1A style · multiple choice · 1 mark

Counting atoms in a hydrate

How many hydrogen atoms are present in 0.0500 mol of MgSO4•7H2O? Use NA = 6.02 × 1023 mol−1. [1]

  1. 3.01 × 1022
  2. 2.11 × 1023
  3. 4.21 × 1023
  4. 6.32 × 1023
Show the answer and the reasoning

Answer: C. C is correct. Each formula unit has 7 water molecules, so 14 H atoms: 0.0500 × 14 × 6.02 × 1023 = 4.21 × 1023. A counts one particle per formula unit. B counts water molecules (7 per unit) instead of hydrogen atoms. D counts every atom in the water (21 per unit), oxygen included.

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The 8 questions in S1.4

  1. S1.4-01 Counting atoms in a hydratePaper 1A style · multiple choice · 1 mark
  2. S1.4-02 Empirical formula from percentagesPaper 1A style · multiple choice · 1 mark
  3. S1.4-03 Empirical formulas for a given MrPaper 1A style · multiple choice · 1 mark
  4. S1.4-04 Ion concentration from a hydratePaper 1A style · multiple choice · 1 mark
  5. S1.4-05 Making and diluting a standard solutionPaper 1B style · data-based · 10 marks
  6. S1.4-06 Water of crystallizationPaper 1B style · data-based · 7 marks
  7. S1.4-07 Empirical formula from combustionPaper 2 style · structured question · 4 marks
  8. S1.4-08 Percentage by mass and atom countsPaper 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.