Description of experiment
Below follows a plain text transcript of the selected experiment.
Needed compounds:
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hydroxyl amine sulfate : (NH3OH)2 SO4
hydrogen peroxide : H2O2
ammonia : NH3
copper sulfate penta hydrate : CuSO4 . 5H2O
sodium hydroxide : NaOH
Class:
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elem=Cu
coordination
redox
Summary:
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In alkaline environments, copper (II) shows remarkable behavior, when brought
in contact with strong oxidizers or reductors.
Description:
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Add an excess amount of a solution of NaOH to a solution of copper sulfate:
A bright blue precipitate is formed.
Add a small amount of NH3 (5% y weight) to the liquid with the blue precipitate
floating around in it: Part of the precipitate dissolves, the liquid becomes
deep blue with light blue particles floating around in it.
Sequence 1:
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Add a large excess amount of H2O2 (3% by weight) to the deep blue liquid with
precipitate: Liquid becomes brown and almost clear. It looks like dark tea,
it only has a little bit greenish hue, which normal tea does not have.
Sequence 2:
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Add an excess amount of hydroxyl amine sulfate to the deep blue liquid with
precipitate: The liquid becomes colorless and clear. No yellow precipitate
of hydrous copper (I) oxide is observed. The solid blue pieces of copper (II)
hydroxide are covered with a yellow layer, but this dissolves again. Finally
all precipitate has dissolved and the liquid is colorless.
Shake colorless liquid well, while keeping contact with air: The liquid
becomes light blue. This light blue color slowly fades away, when the liquid
is left standing quietly. The light blue color is the result of oxidation
to copper (II) by oxygen from the air. Excess hydroxyl amine slowly reduces
this back to copper (I).
Add a highly concentrated solution of NaOH: A little amount of a colorless
gas is evolved (N2 from hydroxyl amine??) and the liquid remains clear and
colorless. After appr. 30 seconds, however, the liquid becomes turbid and
light yellow. Slowly, in the course of a few minutes, the yellow precipitate
becomes thicker. Finally a yellow/brown/orange solid precipitates from the
liquid.