Description of experiment
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Needed compounds:
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hydrogen peroxide : H2O2
ammonia : NH3
cobalt carbonate : CoCO3
nickel carbonate (basic) : NiCO3 . 2Ni(OH)2 . 4H2O
copper carbonate (basic) : Cu(OH)2 . CuCO3
Class:
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elem=Cu,Ni,Co
coordination
Summary:
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Copper and nickel carbonates (basic), which do not dissolve in water, do
dissolve in ammonia, due to formation of a complex with ammonia.
Cobalt carbonate also dissolves, but now an additional reaction occurs,
taking up oxygen from the air.
Description:
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Sequence 1: Copper
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Add some solid basic copper carbonate to ammonia (appr. 15% by weight): The
solid dissolves quickly. The liquid becomes deep blue.
Sequence 2: Nickel
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Add some solid basic nickel carbonate to ammonia (appr. 15% by weight): The
solid dissolves, but the rate at which it dissolves is much lower than the
rate at which the copper carbonate (basic) dissolves. At first glance, when
the powder is added to the liquid, nothing appears to happen. The powder
makes the liquid turbid. However, after one quarter of an hour, the liquid
was almost clear and blue/purple. The intensity of the color is much less
than the intensity of the blue color after dissolving copper carbonate (basic).
Add some H2O2 (3% by weight) to the nickel-solution: No visible changes.
Sequence 2: Cobalt
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Add some solid cobalt carbonate to ammonia (appr. 15% by weight): The solid
dissolves and the liquid becomes brown. When the liquid is shaken, then
it becomes darker (it is shaken with air contact). After a while of shaking,
the liquid is very dark. A thin layer, sticking to the glass, still is strongly
coloured and looks brown/yellow.