Description of experiment
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Needed compounds:
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sulphuric acid : H2SO4
sodium nitrite : NaNO2
potassium bromide : KBr
hydrochloric acid : HCl
potassium chlorate : KClO3
Class:
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elem=Br,Cl,N
redox
Summary:
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A mixture of chlorine and chlorine dioxide oxidizes bromide quickly to
bromine. When an excess amount of nitrite is added, then the bromine is
quickly reduced again to bromide. Addition of an acid does not result in
formation of bromine again.
Description:
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Add some potassium chlorate to concentrated hydrochloric acid (appr. 30%
by weight): Formation of a fairly intensely colored gas mixture. Formation
of this gas mixture is fairly slow. The liquid becomes intense yellow.
Bubble the gas into a bottle of clean water, which is kept upside down under
water. Cap the bottle with the yellow/green gas mixture and shake well: The
liquid is colored light green and a strong underpressure is induced because
of the gas mixture dissolving in the water.
Add an excess amount of potassium bromide to the green liquid: The liquid
becomes orange and a faint brown color of gaseous bromine can be seen above
the liquid.
Add an excess amount of sodium nitrite: The liquid becomes colorless quickly.
No gas is produced.
Add some sulphuric acid and shake: No visible changes.