Description of experiment
Below follows a plain text transcript of the selected experiment.
Needed compounds:
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phosphorus red : P
sodium chlorite : NaClO2
silver nitrate : AgNO3
Class:
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elem=P,Cl,Ag
precipitation
redox
Summary:
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Silver chlorite is stable, but only light heating is required for its
decomposition.
Description:
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Dissolve some sodium chlorite in water and in a separate test tube dissolve
some silver nitrate in water and add the two solutions to each other, while
assuring that an excess amount of sodium chlorite is used: A bright yellow
precipitate is formed. This precipitate looks like powdered sulphur, its color
is slightly lighter. This yellow precipitate is AgClO2.
Let the precipitate settle at the bottom and decant as much as possible from
the liquid above the precipitate. Add a lot of distilled water and let the
precipitate settle again. Filter the precipitate and allow the light yellow mud
to dry on a piece of filter paper. This results in a light yellow solid, which
easily can be scraped off the filter paper and which easily can be crunched
into a powder. The powder looks like powdered sulphur, just a little lighter.
On prolonged standing in light, the powder slightly darkens, but this effect
only is weak. Apparently it is somewhat light sensitive. The darkening may also
be due to the presence of some AgCl in the precipitate (the sodium chlorite
used in the experiment is 80% NaClO2 and 20% NaCl).
Take some of the powder and keep it in a flame: Well before the solid reaches
the flame it makes a hissing sound and it disappears, leaving a small globule
of dark molten material (which seems to be impure silver metal). The
decomposition of the material is fast and self sustaining. However, no flame
can be observed in the decomposition reaction.
Take a really small amount of the yellow powder (e.g. a small pile of a few mm
height) and add appr. 1/3 of this amount of finely divided red phosphorus. By
carefully swirling mix the two powders (do not crunch or scrape). Put the small
amount of powder on a metal spatula and keep it near a flame: The mix explodes
with a remarkably high pitched sound and a very bright orange/white flash with
sparks sprayed around over a distance of 10 cm or so.
Remark 1:
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NEVER scale up this experiment to more than test tube quantities (e.g. at most
a few 100's of mg of reagents may be used) and especially the mix with red
phosphorus should be prepared in really small amounts!
Remark 2:
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The sodium chlorite, used in this experiment must not be strongly alkaline.
Commercially available solid sodium chlorite usually is not strongly alkaline,
but solutions of this chemical are alkaline in order to stabilize the chlorite.
A strongly alkaline solution does not give a yellow precipitate, but a brown
precipitate of hydrous silver oxide.