Description of experiment
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Needed compounds:
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sulphuric acid : H2SO4
sodium nitrite : NaNO2
dimethyl sulfoxide : (CH3)2SO
ferric chloride anhydrous : FeCl3
Class:
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elem=Fe
coordination
Summary:
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Iron (III) forms a very dark brown/red coordination complex with nitrite,
both in water and in DMSO. On acidification, this complex decomposes, giving
a bright yellow solution with a slight green tinge.
Description:
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Sequece 1:
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Add some solid anhydrous FeCl3 to DMSO: The solid dissolves, the liquid makes
some hissing noise on contact, quite some heat is produced. The liquid becomes
deep orange/brown and clear.
Add a small amount of solid NaNO2: The solid partially dissolves. At first, the
liquid becomes red with a brown tinge, on further dissolving of more NaNO2 the
liquid becomes very dark, almost black.
Add a small amount of concentrated H2SO4: As soon as the acid reaches the
liquid, some gas is produced, the air above the liquid becomes light brown,
and the liquid itself becomes intense yellow with a green tinge. The liquid
also becomes a little turbid.
Sequence 2:
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Add some solid anhydrous FeCl3 to water: The solid dissolves, the liquid
becomes yellow brown, and somewhat turbid. As soon as the water reaches the
solid, a lot of heat is produced and the solid very quickly dissolves. There
is, however, no hissing noise, as with DMSO.
Add a small amount of solid NaNO2: Same observation as with the solution in
DMSO.
Add a small amount of concentrated H2SO4: Evolution of a lot of heat, and
violent production of gas. The liquid becomes bright yellow and totally clear.
The air above the liquid becomes brown.
Mix the liquids of sequence 1 and sequence 2: The total liquid becomes clear
and yellow/green. The green tinge is much more pronounced now.