Description of experiment
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Needed compounds:
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hydrazine dihydrochloride : N2H4.2HCl
sodium nitrite : NaNO2
nitric acid : HNO3
Class:
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elem=N
redox
Summary:
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Nitric acid does not show a violent reaction with hydrazine, but instead, a
white solid is formed, which does not dissolve well in the concentrated acid.
Nitrogen oxides do not trigger a reaction, even when these are present, the
reaction with the hydrazine does not set off.
Description:
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Add some solid hydrazine dihydrochloride to concentrated nitric acid: The solid
is covered by a thick white crust and the granules of solid stick to each
other, making on big chunk of solid. The acid does not oxidize the hydrazine.
Most likely, the solid is covered by a crust of insoluble hydrazine dinitrate.
Add some solid sodium nitrite: The solid sodium nitrite reacts with the acid,
giving bubbles of NO and NO2. The reaction is quite vigorous. This gas mix,
however, does not cause the hydrazine dinitrate to react. Nitrogen oxides are
not capable of triggering a reaction.
Heat the liquid with the white solid: The white solid dissolves and a colorless
liquid is obtained. Only when the liquid goes near boiling, the hydrazine is
oxidized by the acid. At that point, the reaction becomes quite vigorous and
self sustained, no external heating is necessary anymore. The liquid remains
colorless and a colorless gas is produced (most likely N2, but it could also be
N2O). The sodium nitrite at this point already does not have any effect
anymore, all of it has reacted and the sodium io
When the vigorous reaction ends, the liquid suddenly becomes yellow. This is
because the chloride from the hydrazine dihydrochloride reacts with the excess
nitric acid, giving an aqua regia like reaction. The color is due to formation
of Cl2 and ONCl.