Cu ions, blue

In that reaction copper is deposited on the zinc and the copper sulfate solution gradually loses its colour as blue Cu ions are replaced by colourless Zn ions. As this reaction takes place, electrons hop from the zinc metal onto Cu ions nearby in the solution. If we were to stand there watching, we would see electrons snapping across from the zinc to the Cu ions wherever the latter came within striking distance of the zinc surface. There would be electron transfer, but no net current of electricity. 

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