Description of experiment
Below follows a plain text transcript of the selected experiment.
Needed compounds:
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sodium persulfate : Na2S2O8
nitric acid : HNO3
glucose : CH2OH (CHOH)4 CHO
ammonia : NH3
silver nitrate : AgNO3
Class:
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elem=Ag,C
coordination
precipitation
redox
Summary:
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When aqueous ammoniacal silver is reduced by glucose, a nice silver mirror
is produced.
Peroxosulfate is capable of oxidizing silver to a higher oxidation state
(+2 or +3), even in acidic environments.
Description:
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Add a little amount of ammonia (5% by weight) to a solution of silver
nitrate: The liquid becomes turbid, a brown precipitate is formed.
Add much more ammonia: The brown precipitate dissolves again. The liquid
becomes clear and colorless. A silver-ammonia complex has formed.
Add an excess amount of solid glucose: The glucose dissolves. The liquid
remains clear. The glass appears to be slightly brownish. After standing
a few minutes no visible change could be observed.
Heat the liquid, such that it just starts boiling and then stop heating:
The glass at first appears to become pale brown/sepia (a brown layer is
deposited on the glass). After approximately 1 minute a nice metallic
layer has deposited on the glass. A shiny silver-mirror has been
produced. The silver mirror is completely opaque. On the inside of the
glass container, the layer is brown/sepia and is not shiny.
Pour off the aqueous liquid from the silver mirror and keep the tube for
one day: The mirror remains intact. The test tube looks as if it is made
of a shiny metal.
Pour some 2M solution of nitric acid in the test tube: Part of the silver
mirror is broken from the glass. Fairly large thin wrinkled sheets of
silver are floating through the liquid. The silver does not dissolve.
Add a large excess amount of Na2S2O8: The solid dissolves and the liquid
becomes turbid and sepia. The wrinkled sheets of silver do not dissolve.
Heat until the liquid boils gently: The silver sheets dissolve, a dark
brown (almost black) precipitate is formed. The liquid starts bubbling
fairly vigorously. The gas which escapes from the liquid is oxygen (tested
with a small burning piece of paper). After a few minutes of gently heating,
the dark brown precipitate has almost completely dissolved and the liquid
becomes almost clear (slightly milky and pale sepia color). When the liquid
is almost clear, the bubbling ceases.