Description of experiment
Below follows a plain text transcript of the selected experiment.
Needed compounds:
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hydrochloric acid : HCl
sodium sulfite : Na2SO3
metol : (CH3 NH C6H4 OH)2 . H2SO4
sodium hydroxide : NaOH
copper sulfate penta hydrate : CuSO4 . 5H2O
Class:
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elem=Cu
precipitation
redox
Summary:
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Metol is capable of reducing copper (II) to copper (I) in alkaline
environments.
Description:
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Add a solution of copper sulfate to a solution of metol/NaOH/Na2SO3 (an
alkaline metol solution, protected with sulfite): The liquid becomes turbid
and dark grey/black. (It might be that the liquid itself is blue, but due to
the dark color of the precipitate this could not be seen.)
Heat liquid to appr. 50 C: Liquid turns brown quickly. Heating for a few
seconds and shaking suffices. When the precipitate has settled, it can be
seen that the precipitate is orange and the liquid is brown/orange.
Decant the liquid and keep this.
Add HCl (10% by weight) to the orange precipitate (with remnants of the
brown/orange liquid): The precipitate turns white for a moment, then it
dissolves. The liquid becomes clear and pale orange (probably due to remnants
of oxidized metol).
Add an excess amount of HCl (10% by weight) to the brown/orange liquid, which
was kept (see above): Liquid remains brown/orange. This brown/orange color
probably is due to an oxidation product of metol.