Description of experiment
Below follows a plain text transcript of the selected experiment.
Needed compounds:
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hydrochloric acid : HCl
sodium metaperiodate : NaIO4
potassium metaperiodate : KIO4
potassium iodate : KIO3
Class:
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redox
elem=I,Cl
Summary:
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Both iodate and periodate form the tetrachloroiodide ion in a strong
solution of hydrochloric acid. A redox reaction occurs, where the iodine
is reduced to its +3 oxidation state and chlorine is released.
Description:
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Add some solid KIO3 to concentrated HCl: The solid partly dissolves and
chlorine gas is evolved vigorously. The liquid becomes golden yellow. On
heating all solid dissolves. On cooling down, nice needle-like crystals are
formed. These are crystals of KICl4.
Dilute the liquid with a lot of water: The yellow solid dissolves and the
liquid becomes brown/yellow. Apparently some iodine is formed and the yellow
solid hydrolyses and disproportionates to iodine and iodate.
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Repeat the experiment with potassium periodate: The results are very similar,
the periodate also is reduced to tetrachloroiodide and chlorine is evolved
vigorously.
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Repeat the experiment with sodium periodate: Again, the results are very
similar, but now it is not possible to obtain a crystalline solid. The
tetrachloroiodide ion still is formed, but the sodium salt of this cannot
be crystallized from its concentrated solution.