Description of experiment
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Needed compounds:
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hydrochloric acid : HCl
cobalt carbonate : CoCO3
Class:
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elem=Co,Cl
coordination
Summary:
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Cobalt (II) ions build pink aqua complexes are intense blue chloro
complexes. Heat favors the chloro complex.
Description:
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Add some solid cobalt carbonate to dilute HCl (10% by weight): The solid
dissolves for a large part in the dilute acid, evolving carbon dioxide.
The evolution of gas produces a lot of bubbling and fizzling. Finally a
pink, but still turbid, liquid is obtained. When left without shaking for
a few hours, a thin layer of a solid remains precipitated.
Heat the liquid, until boiling: The final solid dissolves in the acid. The
resulting liquid is intensely colored, dark blue.
Let cool down to room temperature: The color gradually shifts from dark
blue to pink.
Heat again, until the liquid boils: The liquid becomes intense dark blue
again. On cooling down it becomes pink again.