Strange result in lab possibly electrochem related?

[caracole]

Homework Statement

In a recent lab (our labs are very open ended) my group decided to make 5 different concentrations of CuSO₄. We measured out between .5 g and 10 g of solid CuSO₄ (the pentahydrate kind) into 100mL of water each, dropped a .35 piece of heavy copper foil into each (about 1cmx3cm, maybe smaller), then let all 5 solutions sit for almost a month in a hood with parafilm on top. We also measured the absorbance spectrum of the liquid.

After about one week, the copper foil in the most dilute solutions started to form a slight redish/brown patina. But at this time, there was no measurable difference in the absorbance spectrum of the liquid.

After two weeks, the copper in the most dilute solutions started getting a blue/green chalky looking substance on it. However, the foil in the most concentrated solutions started to get a red shimmery look to it.

Two more weeks and half the foil pieces are covered in this blue/greed stuff and the copper from the two most concentrated solutions are red and sparkley.

We looked at both under a microscope, the red one looks like reddish crystals or copper that was plated onto the foil. It's pretty easy to scrape the red stuff off. The green stuff is also pretty easy to scrape off, it still looks chalky under the microscope, and not shiny at all.

We think the blue green is Cu(OH)₂.
We thought the red stuff was either copper plated onto the foil or Cu₂O crystals (or some combination?) Cu₂O is soluble in acid so we put the foil strip into some 1M acid and nothing dramatic happened, but it did seem a little less red, and a little less sparkley (though still there was something different about the foil).

No significant weight change for any of the foil pieces given the accuracy of our scale :-(

So, my questions (finally) are: Why would something different happen in the concentrated solutions than the dilute ones? How would I have been able to predict this? Is there any other way to tell whether it is more likely that I made Cu₂O or plated more metal onto the foil? Don't you need electricity to plate metal onto things? where would the extra electrons come from?

Homework Equations

The Attempt at a Solution

 

[Nino MMP]

The difference in the reaction between the dilute and concentrated solutions is likely due to the fact that concentrated solutions have higher concentrations of reactants, so the reaction will proceed at a faster rate than in dilute solutions. This means that the copper foil in the concentrated solutions will be reacting more quickly and may produce different products than in the dilute solutions. In order to predict this phenomenon, you would need to know the exact reaction that is happening between the copper foil and the CuSO4 solution. It is likely that the reaction is some form of oxidation/reduction reaction, as the copper will be reacting with the ions in the CuSO4 solution. Knowing the exact reaction and the products that it forms will help you predict what will happen in the different concentrations of solution. In order to determine whether the red substance on the foil is copper plating or Cu2O crystals, you could try submerging the foil in an acid solution. If the red substance dissolves in the acid, then it is likely Cu2O. If it does not dissolve, then it is likely copper plating. In order for metal to be plated onto a surface, electricity is generally required. The electrons necessary for the reaction come from the electric current.