Description of experiment
Below follows a plain text transcript of the selected experiment.
Needed compounds:
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sodium nitrite : NaNO2
sulphuric acid : H2SO4
sodium hydroxide : NaOH
dimethyl sulfoxide : (CH3)2SO
nitromethane : CH3NO2
cobalt chloride : CoCl2.6H2O
Class:
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elem=C,N,Co
coordination
Summary:
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Cobalt (II) chloride hexahydrate is a red/purple compound. When it is heated,
it becomes blue, first dark blue, lateron much lighter blue. The latter
compound is anhydrous cobalt (II) chloride.
Anhydrous cobalt (II) chloride dissolves with a deep blue color in DMSO. With
nitrite, apparently no complex (or a complex with the same color) is formed,
the solution remains deep blue.
The anhydrous cobalt (II) chloride also dissolves in water without problems.
Such solutions are pink. With nitrite these form yellow complexes on
acidification.
Anhydrous cobalt (II) chloride is not soluble in nitromethane.
Description:
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Take a spatula full of solid cobalt (II) chloride hexahydrate and put this is a
glass beaker. Heat over a flame: First, the solid becomes very dark
blue/indigo. This most likely is due to formation of [CoCl4]2-. On further
heating, the solid starts to fizzle and seems to melt. The water boils away.
The color then shifts to purple and the crystalline structure is lost. It
becomes more powdery and amorphous. On still further heating a powdered fairly
light blue solid is obtained, with a somewhat greenish hue
Sequence 1:
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Add some of the blue solid to water: The solid dissolves and the solution
becomes pink.
Sequence 2:
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Add some of the blue solid to nitromethane: The solid does not dissolve, at
least not in any appreciably amount.
Add a lot of water: The blue solid dissolves and the solution becomes pink.
With some stirring, the nitromethane also dissolves.
Add some solution of sodium hydroxide: A blue precipitate is formed. This blue
precipitate has a somewhat greenish hue. The precipitate was allowed to stand
for several minutes, but it did not turn pink. This probably is due to the fact
that the solution was very dilute.
Sequence 3:
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Add some of the blue solid to DMSO: The solid dissolves and the liquid becomes
deep blue with a cyan hue.
Add some solid sodium nitrite, which first was heated to remove water. Part of
the solid sodium nitrite dissolves. It looks as if the color of the solution
becomes a little darker, but there is no noticeable change of color. The
darkening of the solution also is somewhat questionable, it is not impressive.
Part of the solid sodium nitrite does not dissolve.
Add a lot of water: The liquid becomes pink and all DMSO is dissolved in the
water.
Add a small amount of dilute sulphuric acid (appr. 1 mol/l): The liquid shifts
color towards brown/yellow. The solid sodium nitrite which dissolves also
causes the liquid to turn bright yellow/orange. On shaking this bright
yellow/orange color is diluted. Also a little amount of gas is evolved
(bubblng) and above the liquid a very light brown color can be observed.
The orange/yellow compound most likely is a nitrito complex of cobalt.