A student wants to investigate whether the surface area of wood affects how quickly it burns in air. Describe how the student could carry out a fair test to investigate 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).

The student has access to wooden blocks and wooden chips of the same type of wood, a balance, a stopwatch, and a heat source.

Model answer (4 marks)

1. Use the same species of wood for all samples.
2. Keep the mass (or volume) of each sample equal – e.g. cut all pieces to the same mass.
3. Prepare two sets of samples with different surface areas – one large block and one set of small chips.
4. Place each sample on the balance, ignite it with the same heat source and record the time from ignition to flame extinction (or mass loss per unit time).

Examiner tips

  • Use precise wording – e.g. ‘same species’, ‘equal mass’, ‘different surface area’.
  • Show the comparison of two conditions and state that all other variables are held constant.

Common mistakes

  • Mixing up surface area with volume; not keeping mass equal.
  • Failing to specify the same heat source or ignoring air supply as a variable.

Mark scheme (4 marks)

  1. Keep the mass (or volume) of wood the same in each experiment
  2. Use the same type / species of wood throughout
  3. Measure a variable to determine how quickly the wood burns, e.g. time taken for the wood to fully burn / time for the flame to go out / mass lost per unit time
  4. Compare two different surface areas, e.g. one large block versus small chips, whilst keeping all other variables (heat source, surrounding air supply) the same

Key terms in this question

fair test · surface area

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