salt14 Decomposition
of malachite by acid
Malachite is a carbonate
mineral, copper(II) carbonate hydroxide Cu2[(OH)2CO3].
Its crystals have a green colour with characteristic ribbons (Photo 1)
. Its copper concentration is about 57 percent.
Material
Tray, goggles, wellplate6 with two lids, 12 cm of silicon tube (D 2/4 mm),
scissors, insulin syringe, small piece of malachite, dropper bottles with
hydrochlorc acid (< 25%) and with lime water.
Experiment
1. Place a small piece
of malachite into well 1, close it with a lid.
2. Add lime water to well 3.
3. Close both wells with lids, connect the short tube in lid 1 with the
long tube in lid tube with atube.
4. Connect the other tube of lid 1 with a syringe containing 1 mL
of hydrochloric acid.
5. Add the acid drop wise to malachite (Photo 2).
Observations (Photo 3)
In well 1 a green solution
can be seen, gas bubles in well 3. These bubbles make the lime water turbid.
Explanation
The hydrogen ions
of the acid neutralize the hydroxide ions and the carbonate ions are transformed
into carbon dioxide:
Cu2[(OH)2CO3](s) + 4 HCl(aq) --> 2 CuCl2 (aq) +3 H2O(l) + CO2(g)
back............ go on.........first published:
23.03.0703......... ......last modification: 24.03.07