Lecture 1 – Introduction to Electrolysis

ACKNOWLEDGEMENT:

Figure	Source of Figure
Figure 1	http://wps.prenhall.com
Figure 2	http://mypchem.wikispaces.com

Electrolysis:

Electrolysis is the conduction of electricity through ionic solutions; either when ionic compounds are dissolved in water or when molten. These electricity conducting liquids are called electrolytes. Electrolytes; be it ionic solutions or molten ionic compounds contain ions that conduct electricity when it is passed through the electrolyte.

Example 1:

 Electrolyte: Ionic salt solution

Electrolyte: Molten salt

Electrolysis decomposes the electrolyte, usually into its constituent elements.

Electrolysis: Proof of the existence of ions

Ionic compounds are made up of positively and negatively charged ions. In solid state, these ions are held together by strong electrostatic forces of attraction and cannot move, therefore in solid state, ionic compounds are non-conductors of electricity.

When heated to their molten state or when dissolved in water, these ions become free to move and can thus carry current, when applied.

Electrolysis of molten Lead (II) Bromide:

Figure 1:

Figure 1 shows a typical arrangement of an electrolytic cell. For understanding the passage of current, it is important to understand the different components of the cell and their working.

1. The rods dipped in the electrolyte are called ELECTRODES. The electrode connected to the positive terminal of the battery is called the ANODE and the electrode connected to the negative terminal of the battery is called the CATHODE.
2.  Electrodes can be made up of metal or graphite (carbon).
3. Consider the electrolysis of molten Lead (II) Bromide using graphite electrodes.

Figure 2:

Ions present in molten Lead (II) Bromide:

When a potential difference is applied across the electrodes, the anode being positively charged attracts the negatively charged bromide ions. The bromide ions lose their extra electron to the anode and 2 bromide ions discharge together as reddish brown bromine gas.

Reaction at the anode:

Since, electrons are lost at the anode, this is called as ANODIC OXIDATION.

The discharged electrons travel across the battery to the cathode where it is gained by the gathered ions at the cathode.

Reaction at the cathode:

The molten lead is discharged at the cathode. Molten lead is heavy and it drops off from the cathode and settles at the bottom of the cell. Since, electrons are gained at cathode, this is called as CATHODIC REDUCTION.

This discharge or decomposition of Lead (II) Bromide into Lead and Bromine until the entire electrolyte is decomposed.