======Cobalt Chloride Equilibrium======


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**Alternative titles:** Cobalt Blue and Pink Equilibrium
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====Summary====                   
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====Procedure====  
  - Dissolve 5 g of anhydrous cobalt(II) chloride in 250 ml of ethanol in a 500 ml glass flask or bottle.  
  - Prepare at least 250 ml of water in a separate bottle (a plastic bottle can be used for dramatic effect).  
  - Show the audience the flask containing the blue solution.  
  - Add water to the blue solution and observe the color change to deep pink as the equilibrium shifts.



====Links==== 
Cobalt chloride equilibrium lab (Le Chatelier's Principle) - BAMChem: 
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Cobalt equilibrium and thermodynamics - Tommy Technetium:
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📄 "Cobalt colors" experiment - MEL Science: [[https://melscience.com/AU-en/articles/cobalt-colors-experiment/?srsltid=AfmBOopDSnZSBpzZQGb52NU-j5oCeoZGGFxEhD5v4pO5kdXVM_GJGhl6]]\\


====Variations====
None



====Safety Precautions====
  * Wear safety goggles, gloves, and a lab coat.  
  * Cobalt(II) chloride is toxic, irritant, and a suspected carcinogen; avoid skin contact and inhalation.  
  * Ethanol is flammable; keep away from flames or sparks.  
  * Dispose of cobalt-containing solutions as hazardous chemical waste; do not pour down the sink.




====Questions to Consider====
  * Why is the ethanol solution blue before adding water? (Ethanol lowers solvent polarity, favoring [CoCl4]2– formation.)  
  * Why does adding water cause the solution to turn pink? (Water increases polarity, favoring the hydrated [Co(H2O)6]2+ complex.)  
  * How does this demonstration illustrate Le Chatelier’s principle? (The equilibrium shifts to counter changes in solvent composition.)  
  * How would increasing chloride ion concentration affect the color? (It would favor [CoCl4]2–, making the solution bluer.)