Conservation of Mass by Burning Charcoal

Material Analytical balance, big round flask with stopcock, rubber balloon charcoal pieces, oxygen (lecture bottle), calcium hydroxide solution (limewater). 

Observation A special mass of the flask is observed first. The pieces of coal are burning with very bright light, they disappear completely. After burning, no new substance is to be seen, but the mass of the flask is the same as before. The limewater shows the well-known white precipitation the flask is filled with carbon dioxide. 

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