Description of experiment
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Needed compounds:
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sodium sulfite hepta hydrate : Na2SO3 . 7H2O
formaldehyde : CH2O
nitric acid : HNO3
Class:
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elem=N
redox
Summary:
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Nitric acid and formalin react vigorously, but some help is needed in
order to start the reaction.
Description:
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Take a small amount of HNO3 (appr. 52% by weight) (careful, not more than
2 ml) and add half the volume of formalin (appr. 37% CH2O): No visible
reaction occurs.
Heat mixture to appr. 60 C: No visible reaction occurs.
Add a small crystal of Na2SO3.7H2O: The crystal dissolves and a reaction
starts, in which some NO2 is produced. Suddenly the entire liquid seems
to decompose and a violent reaction occurs, in which copuous amounts of
NO2 are formed. The few ml. of liquid results in a large brown cloud of
NO2, expelled from the test tube. The liquid becomes very hot during this
reaction and probably it boils.
After a few seconds the reaction ceases and the liquid remains bubbling
slowly (colourless gas is produced), like soda water.