"Blautopf" (South
Germany), Gate to system of caves
Model experiment:
Corrosion of CaCO3 by CO2
.. salt12 Model
of Karst cave formation:
Corrosion of calcium carbonate (Limestone) by carbon dioxide "Corrosion
means the breaking down of essential properties in a material due to
chemical reactions with its surroundings.(http://en.wikipedia.org/wiki/Corrosion).
In limestone
areas the lime is corroded by water rich in carbonic acid and carbon dioxide:
The acid transforms the insoluble calcium carbonate into calcium hydrogencarbonat
that is dissolved in water and transported away. In countless years caves
and cave systems of all sizes are formed (Photo
1). They may
collapse and filled up with water (Photo
2).
Material Tray
high ampoule (5 ml), Infusion bottle (50 ml) with stopper, plastic pipette
tip, pipette, silikone tube D/d 4/2 mm, Limewater, water, 1/2 effervescent
tablet (about 4 g) (alternative: 1/2 tablet Kaiser Natron and 1/2 teaspoon
full of citric acid).
Experiment 1.
Press the pipette tip through the hole in the stopper from its down side.
Push the tube firmly above it. Add 1/2 of an effervescent tablet to the
bottle.
2.
Fill 1/3 of the ampoule with limewater.
3.
Add 2 pipettes full of water to the tablet, close the infusion bottle.
4.
Dip the free end of the tube into the limewater. Wait until it is transparent
again (Photo 3).
Observations
a) Strong gassing insiede the infusion bottle. Gas bubbles sparle through
the liquid in the ampoule (Photo 3).
b)
The liquid becomes milky and turbid.
c)
After some more time it clears off again
Explanation for
b) Limewater and carbon dioxide reacted forming insoluble calcium carbonate:
Ca(OH)2(aq) + CO2(g) ---> CaCO3(s) + H2O
for c) Insouble
calcium carbonate and more carbon dioxide react. Soluble calcium hydrogencarbonat
is formed: CaCO3(s) + H2O + CO2(g) ---> Ca(HCO3)2(aq)
back.......
go on............first
publication: 18.10.2001...........................................last
modification: 19.01.2012
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