Description of experiment
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Needed compounds:
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sodium hydroxide : NaOH
potassium iodide : KI
nitric acid : HNO3
mercury (II) nitrate : Hg(NO3)2
Class:
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elem=Hg,I
redox
precipitation
Summary:
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Mercury (II) ions produce a bright orange colored precipitate with iodide.
Description:
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Add a slight excess amount of KI to a solution of mercury (II) nitrate in
dilute nitric acid (appr. 3 mol/l): Formation of a very bright orange/red
precipitate, which quickly goes to the bottom of the test tube. The liquid
becomes colorless after the precipitate has settled. The bright orange
precipitate is HgI2.
Leave in contact with air for one day: The liquid above the precipitate has
changed from colorless to pale yellow/brown. Apparently some of the iodide
is oxidized by oxygen from air.
Add a large excess amount of a solution of NaOH: The precipitate dissolves,
the liquid becomes slightly turbid, strongly alkaline and it just is not
colorless. A very pale brown/yellow color can be observed.