Description of experiment
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Needed compounds:
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hydrochloric acid : HCl
sodium sulfide : Na2S . 3H2O
ferric chloride : FeCl3 . 6H2O
Class:
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elem=Fe,S
precipitation
Summary:
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Iron (III) gives a precipitate with S2-, but a redox reaction, resulting
in the formation of sulphur also appears to occur.
Description:
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Add a fresh solution of Na2S to a slightly acidified solution of FeCl3.6H2O:
A black precipitate appears.
Add an excess amount of dilute hydrochloric acid (appr. 10% by weight):
The black precipitate almost immediately dissolves, the liquid looks like
milk after the black precipitate has gone. A strong odour of H2S appears
(rotten eggs). The milk-like liquid is due to the formation of very
finely divided particles of sulphur. The sulphur is created by oxidation
of the sulfide by iron (III).