Description of experiment
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Needed compounds:
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acetone : CH3 CO CH3
potassium nitrite : KNO2
hydrochloric acid : HCl
cobalt chloride : CoCl2.6H2O
Class:
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elem=Co
coordination
Summary:
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Cobalt (II) builds complexes with nitrogen oxides.
Description:
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Add some solid CoCl2.6H2O to dilute hydrochloric acid (10% by weight): The
solid dissolves, the liquid turns pink. The solid does dissolve, but it
does not dissolve as easy as in plain water.
Add some solid KNO2 to the pink liquid: When the crystals of KNO2 touch the
liquid, a gas is evolved. The crystals quickly dissolve and the liquid turns
brown-pink and remains clear. Above the liquid a brown gas can easily be
observed (color of NO2).
Carefully add some acetone, such that it does not mix immediately with the
aqueous solution: The acetone forms a layer on top of the aqueous layer.
The two layers do not have a sharp border, but a transition layer can be
observed, where the concentration of the acetone gradually increases with
increasing height. The thickness of the acetone layer is approximately
one quarter of the thickness of the aqueous layer. The acetone layer is
bright blue (sky blue), there is no brown gas above the acetone layer. The
aqueous layer is brown-pink.
Shake well: The acetone layer mixes with the aqueous layer. The resulting
color is dirty-pink (brownish pink).
Remark: The brown color is expected to be due to formation of a complex
of cobalt and one of the nitrogen oxides. The blue color in the acetone
layer is expected to be due to the color of nitrogen oxide (N2O3), dissolved
in the acetone layer, although it may also be due to some anhydrous cobalt.
After adding the acetone the brown gas above the liquid was gone. It is
expected that this gas dissolved into the acetone.