Description of experiment
Below follows a plain text transcript of the selected experiment.
Needed compounds:
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sodium chloride : NaCl
sodium nitrite : NaNO2
sulphuric acid : H2SO4
hydrochloric acid : HCl
cupric chloride dihydrate : CuCl2 . 2H2O
copper sulfate penta hydrate : CuSO4 . 5H2O
Class:
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elem=Cu,N,Cl
coordination
Summary:
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Nitrite forms a dark green coordination complex with copper (II) ions in
neutral environments. When acidified, then a new coordination complex
(dark blue with a grey hue) is formed in the presence of chloride of
very high concentration. This is not formed when chloride is absent.
Description:
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Sequence 1:
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Add a few drops of water to a mixture of solid cupric chloride and a large
excess amount of sodium nitrite: Both solids dissolve and the liquid becomes
dark green.
Add a few drops of concentrated HCl (30%): Fairly violent formation of NO/NO2
(brown fumes) and the liquid becomes deep blue/grey.
Add a little more HCl (30%): The liquid becomes dark green/brown. This is
probably due to the color of cupric ions in concentrated hydrochloric acid.
Sequence 2:
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Add a few drops of water to a mixture of solid copper sulfate and a large
excess amount of sodium nitrite: Both solids dissolve and the liquid becomes
dark green. No difference with step one of sequence 1.
Add a few drops of fairly concentrated H2SO4 (appr. 50% by weight): Fairly
violent formation of NO/NO2 (brown fumes). The liquid becomes light blue.
The hue of the blue, however, differs from the hue of plain aqueous cupric
ions. The color is a deeper blue, going towards indigo, but the liquid has
no intense color, like with the chloride.
Add some more H2SO4 (appr. 50%): The liquid becomes lighter blue, no further
changes.
Add some solid NaCl: The solid dissolves, the liquid becomes fairly dark
green/brown.