Description of experiment
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Needed compounds:
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sodium hydroxide : NaOH
potassium nitrite : KNO2
acetic acid : CH3COOH
cobalt chloride : CoCl2.6H2O
Class:
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elem=Co
coordination
redox
Summary:
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Cobalt (II) forms a coordination complex with nitrous oxide, which easily
decomposes again. On addition of alkali, the cobalt is oxidized and appears
to build a cobalt-compound of an higher oxidation state.
Description:
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Dissolve some cobalt chloride in dilute acetic acid (appr. 30% by weight):
A pink solution is formed.
Add some solid KNO2: Evolution of a gas at the crystals, when they touch the
liquid. The liquid turns yellowish orange/brown and remains clear.
Heat the liquid to appr. 60 C: A gas is evolved from the liquid, the liquid
turns pink again.
Add a new amount of KNO2 (a fairly large amount): The liquid turns yellowish
orange/brown again. After the KNO2 has dissolved, the liquid still evolves
some gas.
Add a large excess amount of NaOH-solution: Formation of a brown precipitate,
which has a sepia color when diluted. The precipitate does not go to the
bottom of the glass container, but to the surface of the liquid. Tiny bubbles
of gas are formed inside the precipitate. These bubbles cause the precipitate
to go up. After rigorous shaking the precipitate does not go up anymore, it
floats through the liquid as many little brown flakes.