Description of experiment
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Needed compounds:
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sulphuric acid : H2SO4
sodium nitrite : NaNO2
potassium metaperiodate : KIO4
Class:
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elem=N,I
redox
Summary:
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Periodate is capable of oxidizing nitrite ion but only very slowly.
Description:
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Add some potassium metaperiodate to water and shake: Hardly any of the solid
dissolves.
Add a small amount of 2M sulphuric acid and shake again: Still, the solid does
not dissolve easily, but now a visible quantity dissolves.
Add a small amount of a solution of sodium nitrite: The two liquids mix and the
liquid becomes very pale blue. There also is weak bubbling and the air above
the liquid becomes light brown.
Wait for several minutes: The liquid remains light blue, almost colorless.
Let the liquid stand at room temperature for 48 hours: The liquid is light
brown, a compact dark grey and glittering precipitate has settled at the
bottom. The dark precipitate is on top of the remaining undissolved potassium
metaperiodate.
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Remark: The dark precipitate is crystalline iodine and the light brown color is
due to dissolved iodine. Only a very small amount of iodine has dissolved, no
iodide ion is present in the oxidizing mix and hence the solubility of iodine
is very low.