Description of experiment
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Needed compounds:
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hydrochloric acid : HCl
sodium nitrite : NaNO2
acetone : CH3 CO CH3
sodium hydroxide : NaOH
iodine : I2
methanol : CH3OH
Class:
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elem=I
redox
Summary:
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Iodine does not react with nitrite in methanolic solution.
Iodine does react with hydroxide in methanolic solution, a very light yellow
compound is formed. On acidification this gives iodine again.
Iodine does react with red phosphorous in methanolic solution, but the reaction
is slow.
Description:
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Preparation:
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Dissolve some iodine in methanol, a small spatula in a few ml of methanol is
OK. This solution is dark red/brown. This is called solution A.
Sequence 1:
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Add some solid sodium nitrite to solution A: No visible reaction. The sodium
nitrite does not dissolve, at least not visibly. It might be that a small part
of it dissolves. The liquid remains dark red/brown.
Sequence 2:
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Add some solid sodium hydroxide to solution A: Part of the sodium hydroxide
dissolves. The liquid becomes a little warm (like the inside of the hand). The
color of the liquid changes to very light yellow and it remains clear.
Add some water: More of the sodium hydroxide dissolves. The liquid remains
clear and very light yellow. There is a peculiar smell, resembling the smell of
hospitals. It is an "anti-septic" smell.
Add a few drops of hydrochloric acid: Where the drops enter the liquid, a deep
orange/brown color is observed. On shaking, this color disappears again. So, it
seems that most of the iodine has not reacted with the methanol, but
iodine/hypoiodide/iodate is formed, which on acidification gives iodine again.
After shaking, such that the liquid is almost colorless again, add some
acetone: A very small amount of a light yellow precipitate is formed, the
liquid becomes turbid. On shaking, the color disappears and the liquid becomes
totally colorless. This yellow precipitate most likely is CHI3.
Sequence 3:
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Add some red phosphorous to solution A: The powder becomes very finely
dispersed in the liquid, when it is shaken. It looks as if the liquid becomes a
little lighter, but still, quite some iodine remains in solution, while at the
same time, there still is quite some phosphorous in the liquid as well.
Add some water: No strong changes can be observed. Quite some phosphorous still
is suspended in the liquid, while at the same time it also still is strongly
colored yellow/brown.
Add some sodium hydroxide: The yellow/brown color disappears, the phosphorous
quickly settles at the bottom now. Also, a strong smell of phosphine can be
observed now.