Description of experiment
Below follows a plain text transcript of the selected experiment.
Needed compounds:
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nitric acid : HNO3
nickel : Ni
Class:
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elem=Ni
redox
Summary:
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Oxidation of nickel by nitric acid.
Description:
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Add some concentrated nitric acid (appr. 65% HNO3 by weight) to a nickel
coin (dutch 'dubbeltje'): A very slow reaction starts. After a few minutes
the reaction still is very slow. Tiny bubbles of gas appear and the liquid
becomes pale yellow/green. The air above the liquid becomes light brown.
Heat the liquid to appr. 60 C: The reaction remains slow. Nickel does
dissolve in concentrated nitric acid, but the reaction is very slow.
Add a little water to the still warm concentrated nitric acid, such that
the concentration drops to appr. 40% HNO3 by weight:
A violent reaction occurs. The liquid starts bubbling. A thick
red/brown gas appears above the liquid. The liquid itself becomes deep
green. The liquid becomes very hot.
The speed of reaction ceases after some time. Part of the nickel coin does
not dissolve.
Heat the liquid until it starts boiling: The remaining part of the coin
dissolves slowly and the liquid boils, producing suffocating fumes (water-
vapor, mixed with HNO3). After some time, the liquid changes to a thick
darkgreen syrup. At this time, heating was stopped.
Wait for some time: The dark green syrup solidifies to a pale green solid.
The solid becomes hard and brittle. It does not appear to be very
hygroscopic. It is hard to scrape off some of the solid. The solid still
fumes a little bit and has a faint suffocating odour.
This solid probably is Ni(NO3)2.xH20.yHNO3, nickel nitrate with some
nitric acid trapped in the solid (possibly the acid is trapped in
the crystal lattice).
Add some water: The solid dissolves and a bright green liquid is produced.
This liquid is acidic and quite a lot of sodium hydroxide can be added
before the solution becomes opaque due to formation of a finely dispersed
precipitate.