Description of experiment
Below follows a plain text transcript of the selected experiment.
Needed compounds:
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hydrogen peroxide : H2O2
sodium nitrite : NaNO2
sodium sulfite : Na2SO3
hydrochloric acid : HCl
potassium hexa nitrito cobaltate (III) : K3 [Co(NO2)6] . H2O
Class:
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elem=Co
redox
Summary:
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The hexanitrito cobaltate (III) ion can be reduced by SO2 to cobalt (II),
but this reduction requires heating. Some brown compound remains, this
probably is due to the inertness of many cobalt (III) coordination
complexes. With nitrite, a brown complex is formed again. This differs
from the gold/yellow hexanitrito cobaltate (III).
Description:
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Add some cobalt yellow to a strongly acidified solution of sodium sulfite.
The sulfite was acidified with 30% HCl: The liquid becomes yellow and turbid,
due to dispersion of the yellow solid.
Heat the liquid: The liquid starts foaming (evolution of a lot of SO2). A
little later, the liquid becomes blue and clear slowly.
Cool down under running tap: The liquid turns pink. The pink color is not the
bright pink of plain aqueous cobalt (II), there is a brown tinge. The liquid
remains clear.
Add some solid NaNO2 to the still fairly warm pink/brown liquid: Vigorous
evolution of a gas, formation of much brown NO2 above the liquid. The liquid
becomes brown and it remains clear.
Add some H2O2 (10% by weight): Violent evolution of a gas and the liquid
becomes pink immediately.