Electrolysis of Molten Compounds

Electrolysis of Molten Compounds

• Electrolysis (with battery / electricity current) is a process of decomposition / breaking down / separation of a compound (electrolyte) into its constituent elements when electric current passes through it.

Important definition

Anode	Electrode connected to the positive terminal (+) of a battery
Cathode	Electrode connected to the negative terminal (-) of a battery
Anion	Negatively-charged ion. Example: Cl-, SO42- and O2-
Cation	Positively-charged ion. Example: Na+, Zn2+ and Al3+

Classification of electrodes

Inert electrodes	Electrodes that do not take part in chemical reactions during electrolysis	Carbon or platinum
Active electrodes	Electrodes that take part in chemical reactions during electrolysis	Copper or zinc

Electrolysis of Aqueous Compounds (dissolved in water, H₂O)
There are three important factors to determine the types of ions to be discharged at the electrodes.

1. Positions of ions in the electrochemical series
2. Concentration of ions in the solution
3. Types of electrodes used

1. Positions of ions in the electrochemical series
The lower the position of the ion in the electrochemical series, the easier the ion is selectively discharged.
Electrochemical series:

Cation	Anion
K+	F-
Na+	SO42-
Ca2+	NO3-
Mg2+	Cl-
Al3+	Br-
Zn2+	I-
Fe2+	OH-
Sn2+
Pb2+
H+
Cu2+
Hg+
Ag+
Au+

2. Effect of concentration of ions in the solution
The concentration of a particular type of ion is high = ion more likely to be discharged in electrolysis.

3. Types of electrodes used in the electrolysis
There are 2 important notes:

• Inert electrodes: Carbon and platinum (Both of these electrodes do not react with the electrolytes or products of electrolysis)
• Active electrodes: Silver, copper and nickel (Active anode ionises and concentration of cations in the electrolyte does not change)