Description of experiment
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Needed compounds:
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potassium bromate : KBrO3
potassium bromide : KBr
phosphoric acid : H3PO4
Class:
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elem=P,Br
redox
Summary:
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Phosphoric acid is not capable of driving off hydrogen bromide from
alkali bromides, nor does it oxidize bromide.
Description:
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Add some solid potassium bromide to phosphoric acid (appr. 85% by weight):
The solid does not dissolve (or just a small part of it). The liquid remains
colorless and no gas is produced.
Add some potassium bromate: As soon as the solid touches the liquid, it is
covered by a brown/orange layer. After some shaking, the liquid has become
turbid and brown. A finely dispersed white solid seems to be mixed with a
brown liquid. Some small drops of bromine can be observed and a thick
brown vapor of bromine appears above the liquid.