Description of experiment
Below follows a plain text transcript of the selected experiment.
Needed compounds:
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hydrofluoric acid : HF
potassium nitrite : KNO2
Class:
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elem=N,F
acid/base
Summary:
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Nitrite ion is very unstable in concentrated hydrofluoric acid. Although the
acid only is a weak acid, it forces complete decomposition of the nitrite ion
and potassium fluoride remains behind in solution.
Description:
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Add a small amount of solid potassium nitrite to 1 ml of 48% hydrofluoric acid:
As soon as the solid touches the liquid, there is vigorous production of a
brown gas mix. The liquid almost is swirled out of the test tube. The
reaction's speed is similar to the very strong bubblinbg of CO2, when a strong
solution of HCl is added to solid baking soda.
No noticeable heat is produced in the reaction, just a lot of gas. The solid at
once dissolves in the hydrofluoric acid. After the reaction, the liquid is pale
blue, due to formation of a little N2O3.
When this reaction is compared with reaction in H2SO4 or HNO3 of similar
concentration, then one easily sees the more vigorous production of gas with
48% HF.
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This experiment is very dangerous. It must be carried out in a PE test tube or
PE beaker. Do not use glass! Also beware of the strong production of gas. If
you use too much KNO2, then the production of gas is so fast, that the liquid
will foam over the rim of the test tube or may even be ejected from the test
tube. You do not want that to happen with 48% HF! ONLY DO THIS EXPERIMENT IF
YOU KNOW THE DANGERS OF HF!