Chemistry Forum

Confused over what reduces and oxidises in electrolysis. In the question below, how come sulfate isn’t being oxidised? Originally, I answered that the concentration would decrease as I had sulfate as the species undergoing oxidation since it is in the electrolyte.

As it is a solution and water competes to oxidise/react at each electrode, the half reaction with greater potential would be favoured.

I concurred with the sample answer for copper being the cathode, as its reduction cell potential is greater than water’s. Copper ions in solution would deposit onto the cathode. Conversely, water’s oxidation would be favoured in sulfate’s case as it has a more positive potential, releasing oxygen and hydrogen ions which would decrease concentration.

I don’t get how copper is both the oxidising and reducing agent as I always thought the ions in solution are what reacts?

Sulfate is like a boat on a Lake. It carries 2 electons as passengers.
It's negative charged therefor. It travels to the positive electrode called anode and oxidise copper, what means the electrons go of board and copper ions get dissolved. The electrons travel trough the wires of the circuit and reduce at negative electrode called cathode the copper ions, the electrons board again a sulfate boat. The circuit is closed.

ANODE Cu + SO₄ 2- => CuSO₄ + 2 e-
Cathode CuSO₄ + 2 e- => Cu + SO₄ 2-

In the question below, how come sulfate isn’t being oxidised? Originally, I answered that the concentration would decrease as I had sulfate as the species undergoing oxidation since it is in the electrolyte.

Because current density is not high enough. This works only in high concentrated solutions or melted salt and important using inert anodes.

Like Making Peroxidisulfate 2 SO₄ 2- => S₂O₈ 2- + 2e-