Description of experiment
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Needed compounds:
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formaldehyde : CH2O
sodium hydroxide : NaOH
potassium sodium tartrate : NaOOC CHOH CHOH COOK
copper sulfate penta hydrate : CuSO4 . 5H2O
Class:
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elem=Cu
coordination
redox
Summary:
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Formaldehyde is not capable of reducing Fehlings reagent within a few
minutes at temperatures of appr. 60 C.
Description:
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Dissolve some sodium potassium tartrate in a solution of sodium hydroxide,
which contains a suspension of copper hydroxide precipitate: The liquid
becomes clear and blue. The blue color is much more intense than that of
an ordinary copper (II) solution at the same concentration, although not
as intense of that of the copper (II) - ammonia complex. The intense blue
liquid is called Fehlings reagens.
Add some formaldehyde, dissolved in water, to the liquid: The liquid remains
blue. When it is heated to appr. 60 C it still remains blue, even after
several minutes of heating.