Description of experiment
Below follows a plain text transcript of the selected experiment.
Needed compounds:
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sulphuric acid : H2SO4
sodium nitrite : NaNO2
sodium chlorite : NaClO2
Class:
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elem=N,Cl
redox
Summary:
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Sodium chlorite and sodium nitrite do not react with each other in neutral
solution, but when acid is added, they react extremely violently, possibly
explosively.
Description:
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Dissolve some NaClO2 in water. Dissolve a similar amount of NaNO2 in water and
mix the two solutions: No visible reaction occurs. The mixture remains cool.
Add a small amount of dilute sulphuric acid to the mixture: The mixture heats
up considerably. No production of gas is visible.
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Mix a small spatula of solid finely powdered NaClO2 with a similar amount of
solid finely powdered NaNO2: No visible reaction occurs. The powders simply are
mixed.
Add a small amount of dilute (20%) H2SO4: As soon as the acid touches the
powder mix, a loud crackling noise is produced and a few seconds later the
entire mix explodes with a loud bang. Above the mix there is quite some yellow
chlorine dioxide gas, so apparently there was excess NaClO2.
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Dissolve some NaNO2 in water and add some dilute sulphuric acid: A lot of brown
NO/NO2 mix is produced, after a few seconds the gas mix becomes lighter, due to
decrease of the amount of NO2.
Add some solid NaClO2: The pieces which touch the liquid dissolve quickly,
producing a crackling noise. The pieces which stick to the wet glass wall and
are in contact with the brown gas mix become very hot.
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Add some solid NaClO2 to dilute (10%) H2SO4: The solid dissolves, the liquid
turns deep yellow, due to formation of ClO2. Also some ClO2 escapes into the
air above the liquid, the gas mix becomes pale yellow/green.
Add some solid NaNO2 to the yellow liquid: A colorless gas is produced, the
liquid quickly turns colorless when a certain amount of NaNO2 has dissolved.
The liquid becomes warm.
Also some NaNO2 sticks to the wet glass wall. These pieces fizzle a little and
the brown gas mix reacts with the gaseous ClO2, producing white fumes.
Apparently (humid) gaseous ClO2 reacts with (humid) gaseous NO/NO2 mix, giving
a colorless gas and some liquid compound which appears as a white fume. Maybe
HNO3 and HCl?
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Most likely, HNO2 is oxidized by ClO2 and/or HClO2 very quickly in a strongly
exothermic reaction. With solid NaNO2, mixed with solid NaClO2, there is a
dangerously explosive reaction on addition of some dilute acid. DO NOT SCALE UP
THAT REACTION!