What happens if you put a piece of copper into a solution containing Al3+ ions?

This is a question in my studies, and I am a little bit confused! I would think it happens nothing because copper is below aluminium in the reactivity series, right?




You are right with copper does not react with aluminium ions.


But as a side reaction, copper may get slowly oxidized by oxygen and dissolve in mildly acidic solution of aluminium salt. 


Such a thing may happen, if you decalcify copper heating spiral by vinegar and let it stay overnight.


$$\ce{ 2 Cu + 4 CH3COOH + O2 -> 2 (CH3COO)2Cu + 2H2O }$$


Something similar can happen in aluminium salt solutions as well, because of hydrolysis.


$$\begin{align}
\ce{ [Al(H2O)6]^3+ + H2O &<=> [Al(H2O)5(OH)]^2+ + H+} \\
\ce{ 2 Cu + O2 + 4 H+ &-> 2 Cu^2+ + 2 H2O} \\
\ce{ 2 Cu + O2 + 2 H2O &-> 2 Cu(OH)2 v} \\
\ce{ 2 Cu + O2 + H2O + CO2 &-> Cu(OH)2\cdot CuCO3 v} \\
\end{align}$$


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