Description of experiment
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Needed compounds:
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sodium hypophosphite : NaH2PO2
nitric acid : HNO3
Class:
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elem=N,P
redox
Summary:
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Sodium hypophosphite does not react with 68% nitric acid when mixed in the
cold. When the mix is heated somewhat, then the reaction suddenly sets off and
is self-sustained.
Description:
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Add some nitric acid to solid finely powdered sodium hypophosphite: No reaction
occurs. The solid material forms a cake on the bottom of the test tube.
Apparently some hypophosphite is exchanged with nitrate ion and a cake of
sodium nitrate is formed.
Slightly heat the test tube with the solid matter and nitric acid: After some
time, suddenly a violent reaction starts, in which a lot of NO2 is formed. This
reaction is exothermic and sufficient heat is produced to keep it going till
all of the sodium hypophosphite has reacted.