Description of experiment
Below follows a plain text transcript of the selected experiment.
Needed compounds:
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sodium hydroxide : NaOH
potassium ferricyanide : K3 [Fe(CN)6]
potassium ferrocyanide : K4 [Fe(CN)6] . 3H2O
sodium citrate : COONa CH2 COH(COONa) CH2 COONa
vanadyl sulfate : VOSO4.5H2O
Class:
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elem=V,Fe
precipitation
coordination
Summary:
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It is possible to let a liquid completely solidify by making the correct
precipitates. Citrate is very suitable for this, combined with some
transition metals.
Description:
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Add a large amount of solid sodium citrate to a solution of vanadyl sulfate
(slightly acidified with sulphuric acid): Most of the solid dissolves. The
liquid changes from sky blue to intense indigo/blue. A citrate-vanadyl
coordination complex is formed.
Sequence 1:
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Add an excess amount of a concentrated solution of potassium ferricyanide:
The liquid stays clear and brown for a few seconds. Suddenly, however, it
turns turbid quickly and it becomes yellow/green/brown. The liquid completely
solidifies and the test tube can be kept upside down, with not the slightest
deformation of the 'liquid' surface.
Break apart the gelatin-like solid in a few chunks and add water to them:
The chunks do not dissolve, but they give off a large amount of a yellow
substance, which gives a clear yellow liquid. This yellow substance probably
is ferricyanide, trapped in the gelatin-like solid.
Sequence 2:
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Add an excess amount of a concentrated solution of potassium ferrocyanide
to the dark indigo/blue liquid: The liquid instantly becomes very dark,
black. Almost immediately after this, the liquid solidifies and quickly
becomes much lighter with a green/brown color. The solid looks very similar
to the solid, produced in sequence 1.
Pour a solution of NaOH on the solidified liquid: The solution of NaOH stays
above the gelatin-like solid and becomes very light brown. Even when the
test tube is shaken, the solid does not break apart in smaller chunks.
Add some solid NaOH: The pearls of NaOH settle on the gelatin-like solid and
slowly 'eat' their way downwards through the solid. Where the solid NaOH
passes, a brown and clear liquid is left over. When the test tube is shaken,
then the solid breaks apart in larger chunks and finally all of it dissolves.
The final liquid is brown and clear, with a greenish hue.