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Interpretation Part 1: Combustion experiment
Question 1: Why there is much less mass from the ash than we had before from the plants?
Question 2: In which form does the missing mass escape?
Question 3: How long does the escaping mass remain in the air?
Answer 1: Besides from some soot particles (see part 2) the major part of the lost mass escapes as carbon dioxide which is formed during the oxidation with oxygen. If the material was not completely dry also water vapour is formed.
Speak with the students about, what happens during the burning processes: Consumption of oxygen and solid burning material, release of carbon dioxide.
Answer 2: Water vapour and carbon dioxide are gases. The main fraction of the mass escapes as a gas. Only soot particles can be solid.
The students shall understand that gases have a mass, in the same way as solid matter has a mass.
Answer 3: Carbon dioxide is only removed from air again, when it is taken up from new plants during their growth or dissolved in ocean water. Respectively, it can stay for a long time in the air. The particles sink to the ground or they are washed out with the rain. Water vapour enters the water cycle of evaporation, cloud formation and rain.
Explain to the students that carbon dioxide is part of the carbon cycle, in which the growth and decomposition of plants plays an important role and that growing plants take up again the carbon dioxide.
Interpretation Part 2: Filter experiment
Question: Which meaning does this experiment have for the reality?
Answer: All over the world there are always natural and human induced fires of forests and savannahs. This leads to a huge amount of emissions of soot and other particles in the smoke plumes.
The students should understand the transferability of the simple experiment to large scale burning processes in natural vegetation. Please mention the large scale savannah fires in Africa, clearing of woodlands in the South American rain forest and fires in the boreal forests of Siberia.
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