Description of experiment
Below follows a plain text transcript of the selected experiment.
Needed compounds:
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hydrogen peroxide : H2O2
potassium iodide : KI
perchloric acid : HClO4
Class:
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elem=Cl,I
redox
Summary:
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Perchloric acid is very reluctant to reacting with many chemicals. This is
different from what many sites are telling. Perchloric acid only is extremely
reactive when it is anhydrous, the hydrous acid (60 ... 70%) is not that
reactive.
Description:
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Add some solid potassium iodide to 60% perchloric acid: The solid only
partially dissolves, most likely the solid becomes covered by a crust of KClO4.
Heat the liquid with the solid suspended in it, until water is boiling off:
Most of the solid now dissolves, the liquid becomes very pale yellow, but
nothing more. Iodide ion certainly is not oxidized strongly by the perchloric
acid.
Keep on simmering the liquid for more than 10 minutes: Still no remnarkable
change. After 10 minutes the liquid only is pale brown and just a tiny fraction
of the iodide is oxidized to iodine. The air above the liquid remains
colorless.
Let the liquid cool down and add a single drop of 10% H2O2: At once, the liquid
turns deep brown and some grey particles are produced.
Heat the liquid: Purple vapor of iodine can be observed above the liquid.