Description of experiment
Below follows a plain text transcript of the selected experiment.
Needed compounds:
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nitric acid : HNO3
hydrazine dihydrochloride : N2H4.2HCl
Class:
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elem=N
redox
Summary:
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Concentrated nitric acid does not react violently with hydrazine at low
temperature. When the acid is heated, then a reaction occurs. It is remarkable
that such a strong oxidizer does not immediately decompose hydrazine.
Description:
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Add some solid hydrazine dihydrochloride to concentrated nitric acid (60 ..
65%): The solid does not dissolve. It becomes covered by a thick white crust,
and all granules stick to each other making one large chunk of white solid.
Carefully heat the acid with the solid in it: The solid slowly dissolves and a
colorless liquid is obtained. At a certain point, when the liquid already is
quite hot (not yet boiling, but not far from that), then small bubbles of a
colorless gas are produced. This reaction proceeds slowly. On further heating,
the reaction becomes much more vigorous, but it never becomes really violent.
Stop heating the liquid as soon as the vigorous reaction sets in: The vigorous
reaction continues without the external heat source. The liquid is completely
colorless and a colorless gas is produced at a high speed and the liquid
remains rather hot, probably near the boiling point of the nitric acid/water
azeotrope and all solid has dissolved. At a certain point in time, the reaction
suddenly stops. No gas is produced anymore. At that point, the liquid also
suddenly becomes yellow. This effect is really re
Explanation: As long as there is hydrazine, there is a redox reaction in which
a colorless gas is produced (most likely nitrogen, but another possibility is
N2O). As soon as all hydrazine is consumed, the reaction suddenly stops, and at
the same time, a reaction occurs with the chloride from the hydrazine
dihydrochloride, giving rise to the formation of Cl2 and ONCl. These two
compounds give the yellow color and the orange/brown gas mix above the liquid.
This is the standard aqua regia reaction, which only
Add a little more solid hydrazine dihydrochloride to the yellow hot liquid: The
solid quickly dissolves, giving a lot of colorless gas, and the liquid becomes
much lighter again, as long as the hydrazine dihydrochloride is not used up
completely. After the reaction, the liquid becomes more yellow again, but the
effect is not as striking as it was in the first part of the experiment.