Description of experiment
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Needed compounds:
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ammonia : NH3
sodium persulfate : Na2S2O8
hydrochloric acid : HCl
sodium hydroxide : NaOH
ascorbic acid : C6H8O6
copper sulfate penta hydrate : CuSO4 . 5H2O
Class:
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elem=Cu
precipitation
redox
Summary:
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Vitamin C is a strong reductor in alkaline environments. Copper (II) is
reduced to copper (I).
Description:
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Add a solution of copper sulfate to a solution of vitamin C and sodium
hydroxide: Formation of a moss/green precipitate. The color of the
precipitate quickly changes from moss/green to yellow/green. On slight
heating the color changes to orange/yellow. The copper (II) precipitate
has changed to a copper (I) precipitatie, most likely this is very finely
divided Cu2O. The liquid, containing the orange/yellow precipitate is
called ORANGEPREC.
Add an excess amount of dilute HCl (10% by weight) to some of ORANGEPREC:
The orange precipitate dissolves, the liquid becomes clear. The color of
the liquid is light yellow/brown.
Add some solid Na2S2O8 to some ORANGEPREC and shake well: The orange
precipitate quickly disappears. The liquid as a whole first is opaque
orange/yellow, then it turns yellow, light green and finally pale blue.
The final liquid is slightly opaque.
Add an excess amount of NH3 (5% by weight) to some of ORANGEPREC: The
liquid remains opaque and orange/yellow. The precipitate does not dissolve.
Add some Na2S2O8 to the mixture of NH3 and ORANGEPREC: The precipitate
quickly dissolves. the liquid turns blue and becomes clear.