Equilibrium Reactions of Copper and Cobalt Complexes

In the case of reactions involving complex equilibria the influence of the interaction between ions and solvent molecules is generally characterised by means of large color differences. 

Nine test tubes, stand, dropping pipettes, safety glasses, protective gloves. Chemicals 

1 mol/L C0CI2 solution, 1 mol/L CuCb solution, acetone, concentrated hydrochloric acid, 1 mol/L AgN03 solution, solid NaN02 and KSCN, concentrated ammonia solution. 

The addition of hydrochloric acid and thus of Cl ions shifts the equilibrium to the right, which is shown by the blue color in test tube 2. In a somewhat modified manner acetone displaces water molecules from the coordination sphere and leads to the color effects observed in test tube 5. NaN02 forms an orange-yellow colored, solution with Co, ions (test tube 3), while the addition of KSCN leads to the formation of the violet complex [Co(SCN)4]. The Ag ions react with the Cl ions in test tube 2 to give solid silver chloride, which is precipitated from the system, so that the original color of the [Co(H20)6] complex is reformed.  

Dilution of the solution in test tube 6 leads to the formation of the fully hydrated Cu ion. Just as in the case of CUSO4 or Cu(N03)2 this is surrounded by four H2O molecules in the plane and two at the apices of a tetragonally distorted octahedron (D4h symmetry). The addition of concentrated HCl to test 

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