Description of experiment
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Needed compounds:
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potassium hydroxide : KOH
cobalt chloride : CoCl2.6H2O
cobalt sulfate : CoSO4.7H2O
Class:
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elem=Co
precipitation
Summary:
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Cobalt (II) gives a blue precipitate with hydroxide, but this precipitate
quickly turns pink / purple / light brown after its formation.
Description:
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Add a solution of KOH to a solution of cobalt sulfate: Formation of a dark
blue precipitate. After a few seconds, however, the precipitate slowly changes
color from dark blue through grey to pink/purple with a brownish hue.
When a more concentrated solution is used of the cobalt salt, then the final
precipitate has a more pronounced bright pink/purple color.
Add a solution of KOH to a solution of cobalt chloride: Same observation as
with cobalt sulfate. Apparently the chloride ions do not affect the formation
of the precipitate nor its color.