Copper Complexes and Stability

Problem In order to show further phenomena on the structure of complexes and complex equilibria, it should be shown that the central ion is solidly bound to the ligands and is not solely present in the solution, in the stable tetra ammine copper complex. In order to do this, an iron nail is dipped into the complex solution, respectively, diluted sodium hydroxide solution is added and this is compared to regular copper sulfate solution the iron nail does not show the copper deposit as usual, no precipitation of the copper hydroxide is deposited. The copper sulfate solution should be interpreted in comparison to the complex solution as a solution with free Cu2 + (aq) ions or very instable aqueous copper complexes. With the explanation of the copper deposit on iron a cross-linkage to redox reactions (see Chap. 8) is possible. 

Material Test tubes, sand paper iron nail, copper sulfate hydrate, diluted ammonia solution, diluted sodium hydroxide solution. 

Procedure Put diluted blue copper sulfate solution into four test tubes. Add ammonia solution to two test tubes until the deep-violet color appears, don t add ammonia to the other two test tubes. Have two sets of solutions one with 

Observation A copper deposit forms immediately in the light blue solution this can easily be seen when the nail is removed from the solution. A copper deposit does not form immediately in the deep violet solution (only after quite some time). In the light blue solution greenish blue copper hydroxide is deposited, but not in the deep violet solution. 

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