======Chromate – Dichromate Equilibrium======


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**Alternative titles:** Chromate to Dichromate Color Change
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====Summary====                   
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====Procedure====  
  - Dissolve potassium chromate (K₂CrO₄) in water to make a yellow solution.  
  - Dissolve potassium dichromate (K₂Cr₂O₇) in water to make an orange solution.  
  - Place chromate solution into two flasks (1 and 2), and dichromate solution into two flasks (3 and 4).  
  - Add hydrochloric acid (HCl) to one chromate and one dichromate flask. The solutions turn orange as dichromate ions dominate.  
  - Add sodium hydroxide (NaOH) to the other chromate and dichromate flasks. The solutions turn yellow as chromate ions dominate.  
  - Discuss how the observed color change demonstrates Le Chatelier’s principle.



====Links==== 
Metal Complexes 7. Chromate - Dichromate equilibrium - FranklyChemistry: 
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Chromate Dichromate Ion Equilibrium - LeChatelier's Principle Lab Part 2 - 
North Carolina School of Science and Mathematics: 
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📄 CHROMATE/DICHROMATE EQUILIBRIUM - scilearn.sydney.edu.au: [[https://scilearn.sydney.edu.au/fychemistry/demonstrations/files/9.2.pdf]]\\

====Variations====
  * Use smaller test tubes instead of flasks for a classroom-scale version.  
  * Try diluting the solutions to emphasize the difference between yellow and orange more clearly.



====Safety Precautions====
  * Wear safety goggles, gloves, and a lab coat.  
  * Handle chromium(VI) compounds with extreme care - they are toxic and carcinogenic.  
  * Avoid skin contact and inhalation of dusts or vapors.  
  * Collect and dispose of all waste solutions in labeled hazardous waste containers.  
  * Do not pour chromium solutions down the drain.




====Questions to Consider====
  * What color corresponds to chromate ions and what color corresponds to dichromate ions? (Chromate = yellow, Dichromate = orange.)  
  * How does adding acid affect the equilibrium? (Shifts to the right, forming dichromate.)  
  * How does adding base affect the equilibrium? (Shifts to the left, forming chromate.)  
  * Which principle explains this shift in equilibrium? (Le Chatelier’s principle - the system responds to minimize the change.)