Description of experiment
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Needed compounds:
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sodium sulfite : Na2SO3
potassium bromate : KBrO3
vanadyl sulfate : VOSO4.5H2O
Class:
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elem=V,Br
redox
Summary:
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Vanadyl is oxidized by bromate quickly and completely.
Description:
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Add an excess amount of solid KBrO3 to a deep blue (fairly concentrated)
solution of vanadyl sulfate: While the solid KBrO3 dissolves, the liquid
quickly changes color. It changes from deep blue through very dark green to a
final orange color. The gas mixture above the liquid becomes brown, a fairly
large amount of bromine is formed.
Add some solution of sodium sulfite (appr. 1.3 mol/l): The liquid becomes
very dark green, almost black. The vapor of bromine disappears. The solid
KBrO3 becomes covered by an orange/brown layer. On shaking, the solid KBrO3
fairly quickly dissolves and a noticeable amount of heat is produced. The
liquid becomes warm. Apparently there was an excess amount of KBrO3. After a
while, the liquid becomes orange again, a fairly large amount of bromine vapor
is produced and a brown/orange flocculent precipitate is formed.
Dilute with a lot of water: The liquid becomes yellow and a brown/orange
precipitate settles at the bottom.
Decant the yellow liquid and again add a lot of water to the brown/orange
precipitate: The precipitate does not dissolve and the liquid becomes light
yellow.