A student is investigating how the concentration of hydrogen peroxide solution affects the volume of oxygen gas produced when manganese(IV) oxide is used as a catalyst. Describe how the student should carry out a fair and safe investigation, including how they would collect and measure the volume of oxygen produced.

OCR A-Level Chemistry A (H432) — 1.1 Practical skills assessed · Describe · 5 marks · View as Markdown

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

Hydrogen peroxide decomposes into water and oxygen gas. Manganese(IV) oxide acts as a catalyst for this reaction. A student wants to investigate how changing the concentration of hydrogen peroxide affects the total volume of oxygen gas collected.

Model answer (5 marks)

1. Use the same volume of H₂O₂ for each trial, e.g. 50 mL, and the same mass of MnO₂ (e.g. 0.5 g). 2. Keep the temperature constant, e.g. perform the experiment in a water bath at 25 °C. 3. Add the catalyst to the H₂O₂ and immediately collect the evolved O₂ with a gas syringe or by placing an inverted measuring cylinder over a water trough to displace water. 4. Record the final volume of O₂ collected for each concentration. 5. Repeat each concentration at least twice and calculate a mean to improve reliability. 6. Wear safety goggles, handle H₂O₂ carefully as it is an irritant and work in a well‑ventilated area to avoid inhalation of vapours.

Examiner tips

  • Use the same volume of H₂O₂ and catalyst mass to control variables
  • Collect gas with a gas syringe or water displacement for accurate volume
  • Repeat trials and calculate a mean for reliability
  • Include a clear safety statement

Common mistakes

  • Changing the volume of H₂O₂ or the amount of catalyst
  • Not controlling temperature
  • Failing to repeat trials or calculate a mean

Mark scheme (5 marks)

  1. Keep all variables the same except the concentration of hydrogen peroxide (e.g. same volume of hydrogen peroxide solution, same mass of manganese(IV) oxide, same temperature)
  2. Collect the oxygen gas using a gas syringe or by displacement of water (inverted measuring cylinder over water trough)
  3. Record the total / final volume of oxygen gas collected for each concentration
  4. Repeat each concentration at least once (and calculate a mean) to improve reliability
  5. Safety precaution appropriate to this investigation, e.g. wear safety goggles / handle hydrogen peroxide with care as it is an irritant / work in a well-ventilated area

Key terms in this question

concentration · catalyst

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