FACTORS AFFECTING ELECTROLYSIS OF AQUEOUS SOLUTION

Factors Affecting Electrolysis

There are three main factors that can affect the electrolysis products, there are:

Position of ions in the electrochemical series Concentration of ions andType of electrode

Position of ions in the electrochemical series

• The ions at the top of the list is more difficult to be discharged, but as we go down the table, they become easier to be discharged.

• For example:

Cu2+ easier to be discharged compare with H+ 

OH- is easier to be discharged compare with I-.

• This series of ions is called the Electrochemical Series (ES).

• The lower the ion in the electrochemical series, the easier the ion to be discharged during electrolysis.

Electrolysis of Aqueous Sulphuric Acid

At the Cathode At the Anode

Here we have only one ion, the hydrogen, H+ (aq), and each ion gains an electron to become a hydrogen atom.

Here we have a choice of either sulphate, SO4

2- (aq), or hydroxide OH- (aq) ions.

Two of these newly formed atoms then combine to form a hydrogen gas molecule .

Hydroxide is easier to discharge, so oxygen gas is given off at the anode.

Equation:2H+ + 2e- ---> H2

Equation:4OH- ---> O2 + 2H2O + 4e-

Concentration of Ions

• If the concentration of a particular ion is high, it will be selected to be discharged even though it is higher in the electrochemical series compares with another ion present in the solution.

Electrolysis Of DilutedHydrochloric Acid

At the Cathode At the Anode

The hydrogen ions move to the cathode .The hydrogen ions (H+) are discharged.

Both the chloride ions (Cl-) and the hydroxide ions (OH-) migrate to the anode .The chloride ions (OH-) are preferentially discharged because of their position in ES.

Equation:2H+ + 2e- ---> H2

Equation:2Cl- ---> Cl2 + 2e-