Description of experiment
Below follows a plain text transcript of the selected experiment.
Needed compounds:
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hydrochloric acid : HCl
sodium nitrite : NaNO2
potassium nitrite : KNO2
Class:
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elem=N,Cl
redox
Summary:
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Nitrites react with concentrated hydrochloric acid, forming a brown/orange
compound, which remains dissolved in the acid. When the acid is diluted
with water, then this orange compound is destroyed (probably it hydrolyses,
due to lower concentration).
Description:
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Sequence 1:
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Add some solid potassium nitrite to hydrochloric acid (30%): The solid starts
bubbling, when it touches the acid and partly dissolves. A brown gas mixture
is formed, and some finely divided crystalline solid is formed, which slowly
sinks to the bottom as a white precipitate. The liquid above the acid remains
orange/brown, also after several hours. The gas mixture above the liquid
remains pale brown/green.
Sequence 2:
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Add some solid sodium nitrite to hydrochloric acid (37%): Same effect as when
potassium nitrite is added to hydrochloric acid (30%). The slightly higher
concentration and the potassium ions instead of sodium ions have no visible
effect.
Sequence 3:
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Add some solid potassium nitrite to hydrochloric acid (37%): Same effect as
in sequence 2.
Dilute the liquid with the same volume of water: Slight evolution of gas, the
color of the liquid shifts from bright orange/brown to a lighter and less
bright color. Besides becoming lighter, the color of the liquid shifts to
brown and becomes less brightly colored. When the test tube is capped, after
adding the water and the water is mixed, then a slight overpressure is
observed. Part of the white solid dissolves.
Again double the volume of the liquid with water and mix: The liquid becomes
light yellow and again some gas is evolved. The gas mixture above the liquid
is very light and it looks like it is green. Due to the lightness this
observation is not very clear and it might also be very pale brown.
All white solid dissolves.
Add a little more water: The liquid becomes colorless and the gas mixture
becomes very light green (or brown?). A strong smell of chlorine can be
observed.