Description of experiment
Below follows a plain text transcript of the selected experiment.
Needed compounds:
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sodium nitrite : NaNO2
ammonia : NH3
potassium iodide : KI
mercury (I) nitrate : Hg2(NO3)2.2H2O
Class:
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elem=Hg
coordination
redox
Summary:
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Mercurous ions are stable in aqueous solution at room temperature. They do not
hydrolyse, nor disproportionate.
However, when a compound is added, with which a stable mercury(II) complex is
formed, or with which a stable mercury(II) precipitate is formed, then the
mercury(I) disproportionates to the metal and mercury(II).
Description:
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Dissolve some mercurous nitrate in water. This takes quite some time, the salt
is only slowly and sparingly soluble.
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To the solution of mercurous nitrate add a small amount of solution of
potassium iodide: The liquid becomes turbid, a green/yellow precipitate is
formed.
Add much more solution of potassium iodide: The liquid becomes grey and small
droplets of mercury metal settle at the bottom.
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To the solution of mercurous nitrate add a large excess of ammonia: A dark
brown /black precipitate is formed at once, which quickly settles at the
bottom. This most likely is a mix of mercury metal and a mercury (II) ammine
compound.
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To the solution of mercurous nitrate add a large excess of solution of sodium
nitrite: A grey metallic precipitate is formed of small mercury droplets.