Description of experiment
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Needed compounds:
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nitric acid : HNO3
sodium bromide : NaBr
potassium bromate : KBrO3
silver nitrate : AgNO3
Class:
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elem=Ag,Br
redox
precipitation
Summary:
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Silver (I) gives a precipitate with bromate. The compound silver bromate
does not dissolve well in water. When acidified, the compound still does
not dissolve, hence the acid HBrO3 is fairly strongly ionized, otherwise
the silver bromate would dissolve appreciably. The precipitate of silver
bromate, however, still shows strong oxidizing properties, meaning that
it is sufficiently soluble for releasing bromate ions in solution, needed
for the redox reaction to occur.
Description:
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Add a solution of silver nitrate to a solution of potassium bromate: A white
precipitate is formed.
Add a lot of (distilled) water: The precipitate does not dissolve.
Decant the water and add some nitric acid (appr. 2 mol/l): The precipitate
does not dissolve.
Add a small amount of a solution of sodium bromide: The liquid becomes yellow
and some vapour of bromine escapes from the liquid. Inside the liquid, a
pale yellow precipitate is formed. It is not possible to adjust the amount
of bromide, such that no precipitate is formed. As a side effect, probably
some AgBr is formed, which does not dissolve again.