Description of experiment
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Needed compounds:
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nitric acid : HNO3
sodium metaperiodate : NaIO4
thallous nitrate : TlNO3
potassium nitrate : KNO3
Class:
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elem=K,I,Tl
precipitation
redox
Summary:
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Thallium(I) metaperiodate is very much like potassium metaperiodate, but it
decomposes easily due to an internal redox reaction in which thallium(III) is
formed, which forms a precipitate with periodate ion.
Description:
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Prepare a solution of potassium nitrate in one test tube and a solution of
thallous nitrate in another test tube. To both solutions add a solution of
sodium metaperiodate: In both test tubes a compact snow-white crystalline
precipitate is formed. These precipitates are not formed at once, it takes a
few seconds. The precipitates are nicely crystalline and very easily settle at
the bottom. So, Tl(+) ion and K(+) ions have very similar properties in these
experiments. The metaperiodate of both ions is only v
Heat the test tube with the precipitate of thallous metaperiodate: Soon, when
the liquid in the test tube is only luke-warm, a pale yellow color can be
observed in the precipitate. The liquid does not change color, it is the
precipitate which slowly changes color. On further heating the precipitate goes
through colors yellow --> ochre --> brown --> mustard. Finally, a dirty-looking
fairly compact mustard-colored precipitate remains. The change of color is due
to transformation of Tl(+) to Tl(3+). The perio
Add some dilute nitric acid to the precipitate: The precipitate does not
dissolve, not even on heating.
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This is a nice experiment, showing the similar properties of K(+) ions and
Tl(+) ions, with the exception that Tl(+) can be oxidized, while K(+) cannot.
Even the low solubility of some K-salts is nicely mimiced by their
corresponding Tl-salts.