Description of experiment
Below follows a plain text transcript of the selected experiment.
Needed compounds:
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hydrochloric acid : HCl
ammonia : NH3
hydroxyl amine sulfate : (NH3OH)2 SO4
sodium thiosulfate : Na2S2O3 . 5H2O
silver chloride : AgCl
Class:
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elem=Ag,S
redox
coordination
Summary:
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Silver is coordinated by thiosulfate. The silver-thiosulfate complex does
not show any of the reactions of free aqueous silver (I).
Description:
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Add a concentrated solution of sodium thiosulfate to solid silver chloride:
The solid dissolves completely. Some shaking is required, but finally all
of it dissolves and the liquid becomes colorless and completely clear.
Add a solution of hydroxyl amine sulfate: No visible changes. The liquid
remains colorless and clear. Also after a few minutes no changes can be
seen.
Add some ammonia (5% by weight): The liquid remains colorless and clear,
just after adding the ammonia. After a few minutes, however, the liquid
has turned pale yellow/brown and a little turbid. The turbidity slowly
increases, but even after 10 minutes and heating at 60 C the liquid does
not become opaque. It just is a little turbid and a layer of 7 cm can be
viewed through, without problem.
Add an excess amount of HCl (10% by weight): The liquid slowly turns more
turbid. Some white smoke is observed above the liquid (NH3 + HCl). After
a few minutes, the liquid is dirty dark brown/sepia and completely opaque.
A smell of sulphur dioxide can be observed. The thiosulfate decomposes in
the acidic liquid and apparently the silver reacts, either forming metallic
silver or silver sulfide. This is not clear from the color of the liquid.