======Copper Complex Equilibrium======


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**Alternative titles:** Le Châtelier’s Principle
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====Summary====                   
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====Procedure====  
  - Prepare a blue solution of copper(II) chloride in water.  
  - Add sodium chloride or hydrochloric acid to increase chloride ion concentration. Observe the color change toward green or yellow as chloro-complexes form.  
  - Add aqueous ammonia to the solution. Observe the shift to a deep blue color as ammine complexes form.  
  - Dilute with water to reverse the reaction back toward hydrated copper complexes.  
  - Optionally, adjust temperature (warming or cooling) to observe further equilibrium shifts.



====Links==== 
LeChatelier's Principle Demo - Copper Complexes - Mr. Z Physical Science: 
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Le Chatelier's Principle: Part A - Copper(II) and Ammonia Equilibrium - Morgan Stock: 
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====Variations====
  * Add different amounts of chloride or ammonia to observe intermediate equilibrium positions.  
  * Compare the effect of temperature changes on equilibrium.


====Safety Precautions====
  * Safety goggles and gloves required.  
  * Handle ammonia solution in a well-ventilated area.  
  * Take care when handling hydrochloric acid or other strong acids.  
  * Dispose of copper-containing solutions with the appropriate waste.




====Questions to Consider====
  * What color changes occur when chloride is added? (Shift toward yellow-green chloro complexes.)  
  * What happens when ammonia is added? (Formation of deep blue ammine complexes.)  
  * Why does dilution with water shift the equilibrium? (It reduces ion concentration, favoring hydrated copper complexes.)  
  * How does this experiment illustrate Le Châtelier’s Principle? (The equilibrium shifts to counteract the change in concentration of ligands.)  
  * What effect might temperature have on this equilibrium? (It may favor one complex over another depending on whether the forward reaction is endothermic or exothermic.)