Copper Complexes and Equilibrium

Problem The reactions on the transfer of ligands are always equilibria reactions - even in cases of stable ammine complexes the equilibrium lies far in the direction of the complexes. In order to demonstrate equilibria by experiments and to adjust them depending on concentrations, the equilibria between the less stable chloro- and aqua copper complexes are suitable. 

Material Test tubes copper(II) chloride hydrate, solid sodium chloride, concentrated hydrochloric acid. 

Procedure Add water to two portions of green-colored copper chloride solution, then add solid sodium chloride, to the first portion, to the second one hydrochloric acid, and finally add water to both solutions. 

Observation The color of the solutions changes firstly from green to light blue, again to green, finally back to light blue. 

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