Description of experiment
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Needed compounds:
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hydrochloric acid : HCl
hydrogen peroxide : H2O2
sodium bicarbonate : NaHCO3
cobalt sulfate : CoSO4.7H2O
Class:
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elem=Co
redox
precipitation
Summary:
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Cobalt (II) gives a precipitate with bicarbonate, which reacts with hydrogen
peroxide, probably forming a cobalt (III) compound.
Description:
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Add a solution of cobalt sulfate to a solution of sodium bicarbonate: Formation
of a pink precipitate; practically no gas is evolved, there is no clear
effervescence of carbon dioxide. The precipitate does not form momentaneously,
but it takes approximately 10 seconds. The liquid changes from clear to milky,
becoming more and more turbid, until it is completely opaque.
Let liquid stand for a few days: The precipitate has become more compact and
it has turned purple/pink.
Add some hydrogen peroxide (appr. 30% by weight): The precipitate turns brown.
A lot of heat is produced and the liquid starts foaming. The gas produced
probably is oxygen.
Add some hydrochloric acid (appr. 10% by weight): Violent foaming of liquid,
it is ejected from the test tube at high speed. There is a clear smell of
elementary chlorine, although not so strong, that it irritates the nose and
lungs. The violent production of gas was not occampanied by production of
heat. The gas probably was CO2, due to the presence of the bicarbonate.