# Copper chloride color in water electrolysis?

So I tried a simple water electrolysis experiment at home, with NaCl as electrolyte, and a 12 v battery. My wires were made of copper and H2 bubbles were only forming at negative terminal(cathode) on the positive side(anode) nothing was happening. after 3-4 minutes water starting to change into a greenish-blue color and I realized that it must be copper reacting with Chloride ions, after 15 minutes my solution was light blue with exceed NaCl at the bottom, after taking the wires out the solution started to turn into a yellow color in about 10 minutes. So my question is what was the yellow solution and why didn't cathode produce any oxygen?

I'm also worried that the yellow solution might chlorine because I later boiled the solution.

• – Loong Apr 16 '16 at 14:14

The color of the solution is probably due to the presence of blue copper(II) ions ($\ce{Cu^2+}$) and greenish tetrachlorocuprate(II) ions ($\ce{[CuCl4]^2-})$.

The change in color comes from the equilibrium

$$\ce{Cu^2+ + 4 Cl- <=> [CuCl4]^2-}$$

Low concentrations of chloride favor the formation of the blue copper ions. High concentrations of chloride favor the formation of the greenish tetrachlorocuprate ions.

If a significant amount of chlorine had been created you should have observed bubbles at the anode and the typical chlorine smell.

• I wouldn't expect any significant amount of chlorine (or oxygen, for that matter) to appear in this setup. Dissolving the anode is so much easier. – Ivan Neretin Apr 16 '16 at 17:43
• Well I didn't observed any bubbles at the anode but I think it was chlorine I was smelling.(smelled just like swimming pools) I've just noticed bright green color around the anode, I'm assuming that is tetrachlorocuprate(II), after few hours the solution now looks almost clear yet huge amount of blue and yellow precipitation are floating at the bottom. I'm leaving it outside waiting for the water to evaporate. If the blue precipitate is copper (II) or copper(II) chloride ions then what is the yellow precipitated? – alend ahmed Apr 16 '16 at 20:26
• Copper(II) chloride is readily soluble in water, so I would not expect it to precipitate. I guess that the precipitate rather contains copper(II) hydroxide. – aventurin Apr 17 '16 at 16:54