The blue color of a copper sulfate solution fades during electrolysis because copper ions (Cu²⁺) are being reduced at the cathode, forming solid copper metal that deposits on the electrode.

Here's a breakdown:

* Copper sulfate (CuSO₄) in solution: The blue color comes from the hydrated copper(II) ions (Cu²⁺).

* Electrolysis: When an electric current is passed through the solution, the following reactions occur:

* At the cathode (negative electrode): Cu²⁺ ions gain electrons and are reduced to metallic copper: Cu²⁺ + 2e⁻ → Cu(s)

* At the anode (positive electrode): Water molecules are oxidized to form oxygen gas and hydrogen ions: 2H₂O → O₂(g) + 4H⁺ + 4e⁻

* Fading color: As copper ions are removed from the solution to form solid copper, the concentration of Cu²⁺ ions decreases, leading to the fading of the blue color.

In summary: The blue color fades because the copper ions responsible for the color are being consumed in the reduction process at the cathode.