Description of experiment
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Needed compounds:
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potassium iodide : KI
sulphuric acid : H2SO4
nitric acid : HNO3
sodium sulfite : Na2SO3
Class:
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elem=S;N
redox
Summary:
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Nitric acid, mixed with sulphuric acid is a strong oxidizer. It is capable
of oxidizing iodine to iodate.
Description:
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Prepare a mix of concentrated nitric acid (appr. 65% by weight) and concen-
trated sulphuric acid (appr. 98%) and add some solid sodium sulfite: The
solid dissolves and a brown gas is evolved. The liquid becomes pale yellow
and little crystals of a white solid remain floating around in the liquid.
These little crystals do not dissolve. When the liquid is shaken, with the
brown gas above it (NO2), then the brown gas does not disappear.
Add some solid potassium iodide: This solid also dissolves and a gas is evolved
again. Black flakes of a black solid remain floating around in the liquid.
Heat the mixture to appr. 60 C and keep bottle closed during heating: The
gas mixture becomes intensely colored. It becomes brown (not violet). The
liquid does not change very much. No gaseous iodine is created, apparently
the iodine is oxidized further.
Let the mixture cool down to appr. 10 C: The gas mixture above the liquid
becomes pale brown.