Factors Affecting Electrolysis:
In electrolysis, when more than one type of cation or anion is present in a solution, only one cation or one anion are preferentially discharged. This is known as selective discharge of ions.
Position in the Reactivity Series (for cations):
The cations of an element lower in the reactivity series are discharged at the cathode in preference to other cations in the solution. This is because cations of a less reactive element accept electrons more readily.
Relative Ease of Discharge (anions):
The hydroxide ions give up electrons most easily, followed by iodide, bromide and chloride ions. Remember that sulphate and nitrate ions will not be discharged during electrolysis.
Concentration:
If the concentration of a particular ion is high, then this can alter the preferential discharge. The higher concentration makes it more likely to be given off.
Type of Electrode:
Let us take as an example the electrolysis of aqueous copper (II) sulphate solution. If we use carbon electrodes, they will be inert electrodes and will not affect the electrolysis. However, if we use copper electrodes, these are active electrodes and do affect the electrolysis. At the anode, the copper electrode will dissolve into the solution, while at the cathode, the copper ions will be deposited as pink copper metal.