Description of experiment
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Needed compounds:
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hydrochloric acid : HCl
antimony sesquioxide : Sb2O3
sodium sulfide : Na2S . 3H2O
Class:
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elem=S,Cl,Sb
precipitation
Summary:
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Antimony trioxide dissolves in hydrochloric acid, giving a colorless solution.
When hydrogen sulfide is passed through such a solution, then a small amount of
a yellow precipitate is formed and the liquid becomes very pale yellow.
On dilution, much more precipitate is formed and the surprisingly, the color
shifts from pale yellow to orange. The orange solid must be hydrous Sb2S3.
Description:
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Add some solid antimony trioxide to concentrated hydrochloric acid (30% HCl by
weight): Nearly all of the solid dissolves, the liquid remains slightly
opalescent. The solution is colorless.
Take some solid sodium sulfide and add dilute hydrochloric acid to this. When
this is done hydrogen sulfide is produced. Lead this gas through a thin tube
and pass this through the colorless solution of antimony trioxide in
concentrated hydrochloric acid: Initially, nothing seems to change, and the H2S
bubbles through the colorless liquid and part of the H2S dissolves. After some
time, when already quite some H2S has bubbled through the liquid, the liquid
becomes yellow and a small amount of light yellow p
Add a lot of water to the pale yellow (nearly colorless) liquid: A lot of
precipitate is formed, the precipitate has a fairly strong yellow/orange color.
On shaking with more water, the color of the precipitate shifts to a nice
bright orange.
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In the very strongly acidic solution, the Sb2O3 dissolves and SbCl3 is in
solution. With H2S, this hardly reacts and nearly all of the SbCl3 and H2S
coexist in the concentrated acidic solution. On dilution, however, hydrolysis
occurs and the SbCl3 hydrolyses and at the same time reacts with the H2S in
solution. An orange precipitate of hydrated Sb2S3 is formed.