Description of experiment
Below follows a plain text transcript of the selected experiment.
Needed compounds:
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copper : Cu
dichloromethane : CH2Cl2
nitric acid : HNO3
Class:
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elem=C,N,Cl
precipitation
Summary:
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Methylene chloride is capable of extracting nitric acid from its aqueous
solution.
Description:
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Add approximately 1 ml of 65% concentrated nitric acid to 4 ml of methylene
chloride and shake vigorously: A liquid is formed with many small droplets in
it, which only separate slowly (going to the bottom).
Wait for one day: There is a colorless layer at the bottom and a larger light
yellow layer at the top.
With a pasteur pipette take away most of the colorless layer at the bottom and
call this LIQ1. With another pasteur pipette take the light yellow top liquid
and call this LIQ2. There is less than 1 ml of LIQ1 and almost 4 ml of LIQ2.
Experiments with LIQ1
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Add a drop of LIQ1 to water: The drop mixes with the water, but it can be
clearly seen that it is much denser than water.
To the remaining part of LIQ1 add some copper metal powder: The powder reacts
vigorously, a lot of brown gas is produced, the liquid becomes bright blue. So,
LIQ1 contains an appreciable quantity of nitric acid.
Add a little bit more water: A clear sky blue solution is obtained, this is the
color of aqueous copper(II) ion.
Experiments with LIQ2
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Heat LIQ2 in a small 25 ml beaker: The liquid boils away quickly, while the
beaker still can be touched. This is the methylene chloride boiling away, the
temperature only is somewhere between 40 C and 50 C. After some time, when a
small amount of liquid remains (maybe 0.3 ml, but the precise amount was not
measured), the boiling stops and temperature rises. At this point, heating is
stopped. The liquid is bright yellow and is fuming in air.
Add a pinch of powdered copper metal to the small amount of yellow liquid: A
violent reaction starts in which a lot of brown gas is produced, the mass seems
to solidify (humid solid) and becomes dark blue.
Add some water: The liquid becomes green/blue, not a pure color of aqueous
copper(II). A possible explanation is that the yellow liquid contained quite
some chloride besides the nitric acid, which results in formation of a
chlorocuprate(II) complex on addition of the copper.
Conclusion
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Nitric acid can be extracted by methylene chloride, but it also seems to react
a little bit with the methylene chloride (light yellow color, even before the
liquid was heated, and green/blue compound with copper metal). This method does
not seem really suitable for concentrating nitric acid. A lot of methylene
chloride is needed for extracting most of the nitric acid, the aqueous layer
also still contains a lot of nitric acid. This method could be interesting, but
then a good method of recycling the methyl