Preferential discharge of ions during electrolysis

•Electron Transfer
During electrolysis, there is a transfer of electrons which causes oxidation at the anode. The oxidation is as a result of the loss of electrons by the anions. This reaction is called anodic half cell reaction.
At the anode; 2OH-  2e- + H2O + O:
                         2Cl-   2e- + Cl2 (g)
Similar reaction occur at the cathode where actions receive electrons and become reduced. This reaction occurring at the cathode is called cathodic half cell reaction.
At the cathode: Ca2+  + 2e-  Ca (s)
.                            2H+ + 2e -  H2 (g)
Note that oxidation occur at the anode while reduction occur at the cathode. More so, metals or hydrogen gas are discharged at the cathode, while non-metals are discharged at the anode.
Anode: oxidation and non-metals
Cathode: reduction and metals or hydrogen released.
(e.g) Ca(OH)2    Ca2+ + 2OH-
Preferential discharge of ions
During electrolysis, products are formed from the electrolyte and are deposited at the electrodes. The product formed depends on the type of electrolytes used. If the electrolyte is a solution, the products formed may vary because water is used as a solvent. Water ionizes together with the electrolyte and different ions will be produced which moves to the anode and cathode. The different ions in the solution causes competition on which ion should be discharged first.
The products formed at the electrodes will depend on either ions from water or ions from the electrolyte and are discharged with preference to one another. The discharge depends on three conditions, viz;
•The position of ions in the electrochemical series.
•Concentration of ions in the electrolyte/solution
•The nature of the electrodes.