Description of experiment
Below follows a plain text transcript of the selected experiment.
Needed compounds:
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dichloromethane : CH2Cl2
iodine : I2
antimony : Sb
Class:
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elem=Sb,I
redox
Summary:
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Antimony reacts with iodine, giving antimony triiodide. This reaction, however,
is not very fast and quite a large excess amount of finely powedered antimony
is needed to get all iodine reacted.
Antimony triiodide (SbI3) has quite remarkable properties. Its solution is pale
yellow/green, the solid has a bright orange/red color and the vapor is
colorless or nearly colorless. The liquid (molten) material is yellow.
Description:
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Put a small amount of very finely powdered antimony in a test tube. Add a small
amount of iodine (assure that there is a large excess amount of antimony).
Finally add a ml or so of dichloromethane. Swirl the test tube for a while: The
iodine dissolves. The liquid obtains a dark purple color. The liquid remains
purple and very slowly turns a little reddish instead of purple.
Heat carefully, such that the dichloromethane starts boiling and then keep on
heating such that the dichloromethane just simmers a little bit: After a while
the liquid turns wine red instead of purple. After a minute or so, the intense
color disappears and the liquid turns pale yellow with a green tinge.
Let the liquid stand for a minute: The remaining unreacted antimony quickly
settles at the bottom and a perfectly clear pale yellow/green liquid is on top
of the solid antimony.
Decant the liquid into another testtube, such that the antimony remains behind.
After this, boil away the dichloromethane: The boiling away is very easy, due
to the low boiling point of the dichloromethane. A red solid remains behind.
Heat the test tube much more strongly: The red solid turns yellow when it
melts. On stronger heating, all of the yellow material 'disappears'. The test
tube is not filled with a strongly colored vapor. Apparently, gaseous antimony
triiodide is colorless or nearly colorless.
On cooling down, yellow droplets collect on the glass and a red smoke is formed
in the air in the test tube. On further cooling down, the yellow droplets on
the glass solidify and turn red.