...
The
lime-cycle
in nature takes place in 3 steps:
1. Water
and carbon dioxide dissolved in water react
producing carbonic
acid: CO2(l)+ H2O ----> H2CO3(aq)
This acidic
water flows through crevices in limestome.
2. They
react with each other forming calcium hydrogen-
carbonate that
dissolves in water:
H2CO3(aq)
+ CaCO3(s) ---> 2 CaHCO3(aq)
The crevices
enlarge. Next experiment = model for step 3:
3.
Where the groundwater reaches the air limestone
precipitates:
CaHCO3(aq) ----> CaCO3(s) + CO2 + H2O |
|
Lime at
a tap
|
statalactites
in a cave
|
Heating
a clear solution of calcium hydrogencarbonate
|
salt13 Model
of stalagtite formation: Precipitation of calcium carbonate from hard water
"Precipitation
is the formation of a solid in a solution during a chemical reaction (http://en.wikipedia.org/wiki/Precipitation_(chemistry).
Hard
water is a water that is rich in dissolved minerals, mainly calcium
hydrogencarbonate. During washing it reacts with soap. The feeling between
the hands is not soft but hard.
Material
Tray,
high ampoule (5 ml), test tube holder (wire, clothes clamp), ampoule burner
in the stopper of an infusion bottle, hard water (from the previous experiment).
Experiment
Heat
a clear solution (Photo 3) until it is turbid (Photo 2).
Explanation
The
free hydrogencarbonate ions are decomposed in the heat. Carbon dioxidean
carbonate ions are left. These are attracted by calcium ions forming
an unsoluble salt.
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publication: 10.07.2003...........................................last
modification: 01.12.2008