Description of experiment
Below follows a plain text transcript of the selected experiment.
Needed compounds:
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stannous chloride : SnCl2
hydrochloric acid : HCl
sodium chloride : NaCl
palladium chloride : PdCl2
Class:
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elem=Pd,Sn
redox
Summary:
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Palladium probably gives a very finely divided metallic compound, when it is
reduced by stannous chloride. The intense colors, appearing in this
experiment probably are caused by colloidal solutions.
Description:
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Sequence 1:
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Prepare some Na2PdCl4-solution from PdCl2 and a slight excess amount of
NaCl at a concentration of appr. 60 g/l of Na2PdCl4: The liquid is dark
brown and clear.
Add a drop of this solution to some HCl (10% by weight): The liquid becomes
brown and clear.
Add some solid SnCl2: The solid dissolves, the liquid becomes intensely
colored, dark brown, almost black. Just a few minutes later, the color has
shifted from dark brown to dark blue. The color is very intense, a cm of
liquid is completely opaque. A few hours later, the liquid has become dark
green, still very intense. One day later, the liquid still is dark green.
It is hard to determine, whether the liquid is clear or not. If there is a
precipitate, then it is suspended extremely finely into the liquid and
probably it has colloidal nature.
When the liquid is swirled around, then it leaves a clear and bright green
layer, sticking on the glass. This means that it indeed is colored intensely.
After 1 week, the liquid still is green and on the surface of the liquid, a
very delicate silver-like mirror has formed.
Dilute part of the liquid with the silver-like mirror on its surface with a
large amount of water: The resulting liquid becomes red/brown and clear.
Another part of the dark green liquid is added to some solid NaOH: The solid
dissolves and the liquid becomes turbid and yellow/brown.
The third (and final) part of the dark green liquid is diluted with water
carefully, until it becomes red/brown and then some SnCl2 is added: The solid
dissolves and the liquid remains red/brown. It becomes a little opalescent,
probably due to hydrolysis and/or oxidation of tin(II).
Add a some HCl (10%) to the red/brown liquid: The liquid remains red/brown and
it also remains a little opalescent.
Sequence 2:
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Dissolve some PdCl2 in a large excess amount of a solution of NaCl and add some
SnCl2 to this brown solution: The SnCl2 dissolves and the liquid becomes dark
green and appears to be somewhat turbid (probably this is due to the SnCl2,
which always causes turbidity, when dissolved in non-acidic aqueous liquids).
Add some HCl (10% by weight): No visible change.
Dilute with water, such that volume becomes approximately 20 times as large:
Liquid becomes brown and clearly visible dark brown particles are floating
around through the liquid. Now one can clearly speak of a precipitate.