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Equilibrium: pink and blue cobalt

Shift an equilibrium with concentration and temperature (Le Chatelier).

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What you do

1. Add concentrated hydrochloric acid to tube 1, one press at a time, until it turns blue.
2. Now add water to tube 1 (5 mL at a time): the colour goes back to pink.
3. Tube 2: add two presses of the acid (violet), then warm it in the water bath: it turns blue.
4. Move tube 2 to the ice bath (Apparatus → Ice bath): pink again. Which direction is endothermic?

Safety in a real lab

⚠ Cobalt chloride is toxic and concentrated HCl is corrosive: gloves and goggles.

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