A concentrated CuCl2 solution can be reduced to a mixed oxidation state. Whereas CuCl2 has CuCl4(2-) units, I think the active species is Cu2Cl6(3-) (both Cu atoms have a 1.5 charge). This complex has an extremely strong color, deep brown even in thin layers. (On extended boiling with copper metal in a sealed tube, the solution eventually turns from brown to clear as the colorless CuCl2(-) is produced. This solution immediately turns brown on exposure to air.)
I don't think the same happens with sulfate or nitrate solutions. Electrolyzing a copper anode in concentrated NaCl yields a yellow precipitate: very fine Cu2O, produced when copper enters solution as Cu(I), then precipitates when reaching OH-. When electrolyzing in Na2SO4 or NaNO3, a fluffy blue precipitate is produced, Cu(OH)2 (or black CuO when hot), because Cu(I) doesn't enter solution. Presumably, a thin layer of Cu2O exists on the anode, which is then oxidized to Cu(II) and enters solution.
So the point is, in nitrate or sulfate solution, you'll probably get Cu metal only, but in chloride solution, if you don't completely reduce it to metal, you will be left with Cu(I) in solution.
Tim
