According to the activity series positions of copper and ammonium, with ammonium being higher up on the series compared to copper, it would be predicted that ammonium replace copper in a single displacement reaction involving the two elements. Therefore, a reaction between copper and ammonium hydroxide would not be predicted to occur. Despite this, after placing a copper wire in a solution of ammonium hydroxide, the copper appears to react with the ammonium hydroxide, with the evidence for such being the case being that the solution turns from a clear liquid to a light blue-coloured liquid. Do these reactants indeed react? If they do, what are the products? (My suspicion is that the reactants yield copper hydroxide, which is light-blue coloured, ammonia, and hydrogen, as in $$\ce{Cu + 2NH4OH -> Cu(OH)2 + 2NH3 + H2}$$)
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But ammonium is not a metal. It is not on the activity series in the first place. – Ivan Neretin Mar 20 '17 at 21:52
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Did you exclude air from the solution? Air could oxidize the copper. – Oscar Lanzi Mar 20 '17 at 22:54
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But the problem is that copper(II) hydroxide will further react with ammonia solution to form tetraammine complexes and other various copper-ammine complexes and thus you will not get a definite product and only get a mixture of compounds. – Nilay Ghosh Mar 21 '17 at 03:57
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@NilayGhosh I object. You will get $\ce{Cu(NH3)42}$, and that's pretty definite. – Ivan Neretin Mar 21 '17 at 05:18
1 Answers
No, I believe that copper(II) hydroxide will not form rather a soluble copper-ammonium complex will be formed.
This handbook discuss the corrosion of copper in ammonium hydroxide solution:
Copper and copper alloys suffers rapid attack by concentrated solution of ammonium hydroxide to form a soluble complex of copper-ammonium compound. In some cases, the corrosion of copper exposed to dilute solution of ammonium hydroxide is low. Copper specimen submerged at room temperature for one week in 0.01N ammonium hydroxide solution suffered a weight loss of 3.5mil/yr.
Also, this paper discuss the rates of Copper Dissolution in Aqueous Ammonium Hydroxide Solutions:
The rates of dissolution of polycrystalline metallic copper in aqueous ammonium hydroxide solutions have been determined under various experimental conditions. Over a considerable range of conditions the dissolution has been found to be autocatalytic. An empirical equation is presented which represents the autocatalytic rate data with an average deviation of $\ce{\pm4\%}$. The rate equation is discussed in terms of a mechanism which assumes that the rate controlling process is the removal of cuprous ion species from the copper solution interface by diffusion. Data are also given for an essentially zero-order rate of dissolution observed when the dissolving medium was concentrated with respect to oxygen or very dilute with respect to cupric ion species. The autocatalytic dissolution is well represented by a half-order rate equation.
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