Description of experiment
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Needed compounds:
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sodium hydroxide : NaOH
hydrochloric acid : HCl
thiourea : NH2 CS NH2
copper sulfate penta hydrate : CuSO4 . 5H2O
Class:
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elem=Cu
redox
Summary:
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Copper (II) reacts with thiourea, forming a pale/yellow precipitate, looking
like sulphur. This precipitate, however, is not sulphur (what is it???).
Description:
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Add a solution of copper sulfate to a solution of thiourea: The resulting
liquid becomes turbid and almost white. It slowly, however, turns light
blue again and the precipitate particles stick together, forming one large
chunk.
Decant the pale blue liquid and rinse a few times with water: The precipitate
does not dissolve. The color of the precipitate is pale yellow.
Remove the water and add some hydrochloric acid (appr. 10% by weight): A small
part of the precipitate seems to form a sponge-like structure and forms small
white-semitransparent jelly-like flakes, floating around in the liquid. Most of
the precipitate, however, does not change appearance.
Decant the acid and rinse a few times with water and add some solid NaOH and
a little amount of water: The NaOH dissolves and the precipitate becomes
black. A large black chunk is formed and many smaller black particles float
around in the liquid.