Description of experiment
Below follows a plain text transcript of the selected experiment.
Needed compounds:
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sodium dithionite : Na2S2O4 . 2H2O
sodium persulfate : Na2S2O8
hydrochloric acid : HCl
sodium hydroxide : NaOH
hydroxyl amine sulfate : (NH3OH)2 SO4
potassium ferricyanide : K3 [Fe(CN)6]
potassium ferrocyanide : K4 [Fe(CN)6] . 3H2O
Class:
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elem=Fe
coordination
redox
Summary:
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Ferrocyanide and ferricyanide react with hydroxyl amine in an unexpected way.
The ferri complex first decolorizes, but then a new colored compound is
formed. The ferro complex shows this behaviour immediately.
Description:
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Sequence 1:
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Add some potassium ferricyanide to a solution of hydroxyl amine sulfate: The
solid dissolves, the liquid becomes intense yellow, just like a plain
solution of potassium ferricyanide. A very slow evolution of a colorless
gas can be observed. The liquid remains clear.
Add a few pearls of sodium hydroxide: The solid dissolves. The liquid slowly
decolorizes. After a few minutes it is almost colorless. It remains clear.
Add a little amount of potassium ferricyanide again: The liquid again becomes
yellow when the solid dissolves.
Heat the liquid: The liquid decolorizes again, much faster now. It does not
become completely colorless, however. From a certain point, where it is
almost colorless, the color intensifies again. After a few minutes the liquid
has become yellow/green and it has become turbid. It looks as if the liquid
reacts with a component from the air. At the surface of the liquid a blue
compound is formed. When the still warm liquid is shaken, with air-contact,
then it quickly becomes more turbid and dark green.
Sequence 2:
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Add some potassium ferrocyanide and hydroxyl amine sulfate to water and
dissolve all of the solids: The liquid becomes pale yellow (almost colorless)
and remains clear.
Heat to almost boiling and keep hot for a few minutes: The liquid turns more
and more yellow. At a certain moment it becomes a little turbid and it becomes
yellow/green. When heating continues (with gentle boiling), the color becomes
darker and shifts more and more from green/yellow to dark blue/purple. Finally
the liquid is almost opaque and dark blue/purple.
After a few hours of quiet standing, it can be concluded that the liquid
itself is not dark blue/purple. The final result is a yellow/green liquid,
with a dark blue/purple solid (*) at the bottom.
Add a concentrated solution of NaOH to the clear yellow/green liquid: The
liquid becomes orange/brown and remains clear.
Add a concentrated solution of NaOH to part of the dark blue/purple solid (*):
The solid becomes brown. When the liquid is shaken, the brown solid does
not dissolve, the liquid becomes brown and turbid.
Add hydrochloric acid (appr. 10% by weight) to a part of the dark blue/purple
solid (*): No apparent changes, the solid does not dissolve nor does it change
color.
Add a solution of Na2S2O8 to a part of the dark blue/purple solid (*): No
apparent changes, the solid does not dissolve nor does it change color.
Add a solution of Na2S2O4 to a part of the dark blue/purple solid (*): No
apparent changes, the solid does not dissolve nor does it change color.
The color of solid (*) strongly depends on how it is watched. When light is
falling on it, it looks dark blue/purple/black, depending on the exact type
of light (SL light or tungsten light). When light is falling through (on
shaking some water with some of the solid) then it looks pale blue milky
with SL light or greyish green with tungsten light.