Al in CuSO4

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Why an acqueous solution of CuSO4 doesn't react with an aluminum foil, but, if we add a little amount of NaCl, the reaction starts immediately?

mrjeffy321

Aluminum should react with an aqueous solution of since it is a more reactive metal, it should displace Copper ions out of solution.
However, the rate of this reaction might be very slow and possible the thin protective coating of Al2O3 on the Aluminum metal prevents the reaction from occurring.

However, by adding NaCl to a solution of CuSO4, you are forming a solution which is ionically equivalent to CuCl2. A Copper (II) Chloride solution acts as an acid and will react with Aluminum metal quite readily.

dtx

If you want to investigate the reaction without the NaCl, I would recommend sanding the Al foil to remove the oxide coating. Also, you can try to gently heat the reactants until you start to see someting happening. You can try using more a concentrated CuSO4 solution as well.

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What makes an acqueous solution of CuCl2 different from a solution of Cu++ and Cl- separately? Do you mean that, maybe, Cu++ partially oxidizes Cl- to Cl2 wich reacts more easily with Al (covered with its oxide)?

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I already know that Al without the oxide layer reacts immediately even with water itself, forming again the oxide layer.