Description of experiment
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Needed compounds:
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hydrogen peroxide : H2O2
sodium hydroxide : NaOH
sodium sulfide : Na2S . 3H2O
hydrochloric acid : HCl
antimony sesquioxide : Sb2O3
Class:
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elem=Sb
coordination
Summary:
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Sulfide is capable of forming a brightly coloured compound with antimony
(III) in a strongly acidic environment. The sulfide is not destroyed by
strong acid and is not converted to hydrogen sulfide gas.
Description:
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Add some Sb2O3 to hydrochloric acid (appr. 10% by weight): The solid
dissolves and the resulting is colorless and almost clear.
Add a little amount of a solution of sodium sulfide to the acidic solution
at once. The volume of the added solution is approximately the same as
the volume of the acidic solution of Sb2O3: Formation of an orange
precipitate. The orange color is not a very bright one, there is a dull
brownish shade over the bright color. The odour of H2S can be observed,
but there is no bubbling/foaming of the liquid. There is, however, a
slight overpressure in the testtube with the mixed solutions.
Pour out the liquid, containing the orange precipitate, in a large amount
of water (appr. 25 times its own volume): The orange precipitate quickly
goes to the bottom of the beaker. The liquid above this precipitate
is slightly turbid and has a very light yellow color.
Rinse the precipitate by adding it to a large amount of water and letting
it settle, before the water is replaced by a fresh amount. Repeat this
rinsing three times. To the final resulting precipitate, contained in a
little amount of water, add an excess amount of NaOH: The solid dissolves,
the orange precipitate dissolves and the resulting liquid becomes almost
clear and colorless. Just a faint yellow color can be observed.
Add some hydrogen peroxide (appr. 6% by weight): No visible changes.
Add a small amount of hydrochloric acid (appr. 10% by weight): Where the
acid touches the liquid, it becomes intense yellow/orange, but when it is
shaken again, the color becomes very pale yellow again (almost colorless).
Add much more hydrochloric acid (appr. 10%): The liquid becomes yellow/
orange and an orange precipitate is produced, which floats around in the
liquid in the form of fairly large flakes. The color of this precipitate
is much brighter than the color of the precipitate, which was formed on
the addition of the solution of sodium sulfide.