Description of experiment
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Needed compounds:
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sodium sulfide : Na2S . 3H2O
hydrochloric acid : HCl
nitric acid : HNO3
antimony : Sb
Class:
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elem=Sb
redox
Summary:
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Elementary antimony dissolves in aqua regia at a fairly high rate. While
it dissolves a lot of gas is produced. When the liquid is diluted with
water, then a white precipitate is formed, due to hydrolysis of the
reaction product. It looks as if the antimony is oxidized to the +3 oxidation
state.
Description:
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Mix 1 part of nitric acid (52% by weight) with 3 parts of concentrated
hydrochloric acid (30% by weight) and add a piece of antimony to it: No
visible reaction. The liquid remains colorless.
Heat the liquid to approximately 60 C: A gas is evolved at the antimony,
the liquid becomes yellow and remains clear. The gas mixture above the liquid
becomes yellow/brown. Is the yellow color of the liquid, due to decomposition
of the aqua regia or is this due to the color of one of the reaction products
of the antimony?
Wait some time: Finally, all antimony has dissolved. The liquid is deep yellow.
A very small amount of a white flocculent solid remains as well.
Dilute with water approximately 5 times: A thick white precipitate is formed.
The liquid becomes white and totally turbid. After some time, the precipitate
settles and some water can be decanted.
Add some concentrated hydrochloric acid: Most of the white precipitate
dissolves. The liquid becomes very pale yellow.
Pour out the contents of the test tube in a beaker full of water: The liquid
in the beaker becomes slightly turbid.
Add a solution of sodium sulfide: An orange/yellow precipitate is formed at
once. Besides this, a smell of rotten eggs can be observed.