Description of experiment
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Needed compounds:
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sulphuric acid : H2SO4
sodium nitrite : NaNO2
methanol : CH3OH
Class:
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elem=C,N
organic
Summary:
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Methanol reacts with nitrites in the presence of acid and of water. A
colorless gas is produced. Is this methyl nitrite? Without the water, or
without the acid, no reaction occurs.
Description:
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Add some sodium nitrite to methanol: Part of the sodium nitrite dissolves in
the methanol. The solution remains clear and colorless, with some of the
solid sodium nitrite at the bottom.
Add some sulphuric acid to another amount of methanol: The acid mixes with
the methanol. Quite a lot of heat is produced.
Mix both liquids based on methanol, the one with acid and the other with
sodium nitrite: A white flocculent precipitate is formed. Is this white
precipitate Na2SO4 or NaHSO4, which does not dissolve well in methanol?
On the bottom of the test tube, still the solid remains of sodium nitrite
are visible.
Add a few drops of water: The white precipitate partly dissolves.
Add a few more drops of water: The white precipitate dissolves. A small
amount of a colorless gas is eveolved, no brown color of NO2 can be observed.
A kind of crackling noise is produced on the solid NaNO2.
Add more water, now the total volume of water is comparable to the total
volume of methanol: A fairly vigorous evolution of a colorless gas can be
observed on the solid NaNO2. Most of the solid now dissolves. Finally, the
evolution of the gas goes much slower. A small amount of NaNO2 then still
is present. The gas only has a faint odour, or it is odourless. The odour
observed may also be due to the presence of methanol.
While gas was produced, the test tube was loosely stopppered.
Bubble the gas contents of the test tube in another test tube, which is
filled completely with water and kept upside-down in a large tub of water.
After this, one has a test tube, filled with the colorless gas and some
fairly clean water.
Light a piece of tightly rolled paper (making kind of paper stick) and put
this in the test tube with the colorless gas: The paper does not burn in the
gas, it looks however, like the gas itself burns a little. After the paper
is extinguished, a small amount of brown NO2 can be observed. From this can
be concluded that the gas at least contains nitrogen.