Equilibrium in copper(II) chloride solution

Equilibrium of blue and green solution

Scientific name: The equilibrium between two colored copper species in aqueous solution

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Equilibrium in copper(II) chloride solution

by ChemToddler

copper chloride equilibrium

by Napier Boys' High School Science Department

Not all Cu 2+ solutions are blue Copper (II) chloride solution is GREEN

by peter s p Lim

copper chloride equilibrium

by Napier Boys' High School Science Department

Safety

Wear eye protection goggles. Be careful with the concentrated acid!

Always follow general safety recommendations. Please note that conducting chemistry experiments you must comply with the relevant legal procedures in your country.

Reaction formula

(Cu(H2O)6)2+(aq)(blue) + 4Cl-(aq) ↔ (CuCl4)2-(aq)(green) + 6H2O

Step-by-step instruction

  1. Take 2 g of solid copper(II) chloride and dissolve it in 10 ml of water in a 150 ml heat resistant beaker. Now you have a blue solution.
  2. Add a small amount of concentrated hydrochloric acid to the beaker. Now you have a yellow-green solution.
  3. Add water to the beaker to make the solution light-blue.
  4. Add a small amount of hydrochloric acid to make the solution green.

Scientific background

The two different colored Cu(II) complex ions, (Cu(H2O)6)2+ and (CuCl4)2-, exist together in equilibrium in the solution in the presence of chloride ions.

(Cu(H2O)6)2+(aq)(blue) + 4Cl-(aq) ↔ (CuCl4)2-(aq)(green) + 6H2O.

Chemical equilibrium behaves according to the Le Chatelier’s principle. It can be stated as "When a system at equilibrium is subjected to change in concentration, temperature, volume, or pressure, then the system readjusts itself to (partially) counteract the effect of the applied change and a new equilibrium is established."

In this experiment, when we add hydrochloric acid to solution, the equilibrium shifts to the right to compensate for the excess of chloride ions. The result is the formation of (CuCl4)2-. When we add water, the equilibrium shifts to the left and the result is (Cu(H2O)6)2+. These two complexes have different colors because they have different geometries and different ligands around cobalt ion.

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Published on 13 April 2015

  • Fire
  • Heating with fire
  • Explosion
  • Poisoned gas
  • Organic
  • Electricity
  • Solution
  • Oxidation reduction
  • Color change
  • Precipitate
  • Gassing
  • Catalyst