A student wants to find out whether the mass of a catalyst affects the rate of decomposition of hydrogen peroxide solution. Describe how the student could carry out a fair and reliable investigation to test this.

Cambridge International IGCSE Chemistry (0620) — 12.1 Experimental design · Describe · 4 marks · View as Markdown

Written & reviewed by James Millett — Biology (Imperial College London), PGCE Science (University of Cambridge).

Model answer (4 marks)

1. Prepare a fixed volume of hydrogen peroxide solution in a graduated cylinder.
2. Measure the volume of oxygen gas produced in a gas syringe over a set time interval.
3. Keep the temperature, concentration of H₂O₂, surface area of the catalyst and the reaction time constant.
4. Vary only the mass of the catalyst – use at least three different masses (e.g. 0.1 g, 0.3 g, 0.5 g).
5. Perform each mass trial at least twice and calculate the mean volume of O₂ produced to improve reliability.

Examiner tips

  • Use the same temperature and H₂O₂ concentration for all trials
  • State clearly that only catalyst mass is varied
  • Include a mean calculation to show reliability

Common mistakes

  • Changing temperature or H₂O₂ concentration between trials
  • Using the same mass of catalyst for all trials
  • Not calculating a mean or repeating trials

Mark scheme (4 marks)

  1. Measure the volume of oxygen gas produced as an indicator of the rate of reaction
  2. Change only the mass of catalyst while keeping all other variables constant
  3. Use at least three different masses of catalyst to identify a trend
  4. Repeat each experiment and calculate a mean to improve reliability

Key terms in this question

catalyst

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