What gas would be produced in a dilute copper chloride electrolysis reaction?

Question

In a CuCl2 electrolysis reaction the gas produced is Cl2.

What gas would be produced if the copper chloride was dilute?

Answer 1

You would still get some Cl2 (at the anode), but you would also start to get some H2 (at the cathode) and some O2 (also at the anode).  Copper(II) is easier to reduce than hydrogen (check reduction potentials), but when the concentration of copper is much lower, the reduction of hydrogen, from the water in the solution, becomes more favorable (see the link for the Nernst equation for a description of this effect), and so some H2 is produced.  The same effect occurs for O2 at the anode, when the oxide ion in water is oxidized.