An electrolytic cell is set up. Two inert electrodes are attached to an external 6V battery, and are placed into a solution. The solution is a 1.00 M aqueous solution of calcium iodide (CaI2 (aq)). Determine which half-reactions are happening at the cathode and the anode of the electrolytic cell and explain your answer.
My teacher uses half reaction with water to solve but I don't understand how you chose which water half reaction to use since there are three of them
They use 2 H2O (l) + 2 e- ---> H2 (g) + 2 OH- (aq) Enot = -0.83 V
for the reduction reaction
For the oxidation reaction they use: 2H2O (l) ----> O2 (g) + 4 H+ (aq) + 4e- Enot = -1.23 V
Please explain why