Description of experiment
Below follows a plain text transcript of the selected experiment.
Needed compounds:
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sodium sulfite : Na2SO3
iodoform : CHI3
Class:
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elem=C,I
organic
Summary:
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Iodoform is only moderately stable. On heating, it decomposes to iodine, carbon
and hydrogen iodide. This process of decomposition looks quite special.
Description:
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Put a spatula full of iodoform in a test tube and then slowly heat the test
tube: The iodoform seems to melt, but at that point, its color also darkens and
a faint purple vapor can be seen already. Quickly, the purple color becomes
denser and in cooler parts of the test tube, nice fern-like crystals of iodine
are deposited on the glass wall. There also is a brown/red color in the vapor,
especially somewhat higher (in cooler places). At the open end of the test
tube, a faint fume can be observed. This is due to the presence of HI gas,
which reacts with humidity in the air, giving fine droplets of HI, dissolved
in water (similar to the effect of fuming of HCl and strong hydrochloric acid
in contact with air).
Let the test tube cool down and add a solution of sodium sulfite: The crystals
of iodine dissolve, all brown/red material also disappears and finally a
colorless liquid remains, with black particles floating in it. The black
particles are the remaining carbon.
The decomposition has net equation: CHI3 --> C + HI + I2
In reality most likely there also will be side reactions, in which compounds
with more than one C-atom are formed.