What is the mechanism of electrolysis?

Answer 1

Mechanism of Electrolysis

The process of electrolysis is exactly opposite to one that takes place in a voltaic cell. A voltaic cell or a battery uses its chemical energy to produce electrical energy. While in electrolysis, electrical energy is used to bring about a chemical change. Humphrey Davy (1807) showed this in his experiments, when he isolated potassium by passing electricity through molten potassium hydroxide.

The phenomena of electrolysis can be explained by the extent to which the molecules of an electrolyte can disassociate (or break up) into electrically charged ions in a specially designed apparatus called electrolytic cell.

The Electrolytic CellBack to Top

An electrolytic cell consists of a container made either of glass, or any suitable plastic material called electrolytic tank, which is a bad conductor of electricity. Two electrodes (rods or plates) are placed in the tank and it is filled with the solution of the electrolyte or with molten electrolyte. An electric current called the Direct current (D.C.) is passed through the solution by connecting the electrodes to a battery.

Remember :

For electrolysis it is necessary to have the flow of the current in one single direction throughout, i.e., the current must be a D.C. (direct current). In the laboratory we get a D.C. (direct current) by using a dry cell or a lead accumulator battery.

The normal domestic current is an A.C. (alternating current), in which the direction of the current is altered every small fraction of a second. Electrolysis cannot be easily carried out with an A.C current, as accumulation of electrons on one plate at any given instance of time does not take place.

The electrolytic solution or the molten electrolyte used contains negative or positive ions that move freely throughout the solution. When an electric current is applied across the solution through the two electrodes, ions move towards the respective electrodes: cations (positively charged ions) move towards the negative terminal called cathode, and anions (negatively charged ions) move towards the positive terminal called anode. Thus, electrons flow in one particular direction through an external conducting wire connecting the two electrodes.

On reaching the electrode surfaces, these ions take part in chemical reactions. The cations get reduced at the cathode, while the anions get oxidized at the anode. Thus, the electrolyte gets decomposed into its constituent ions by the passage of electricity.

The products of these electrode reactions,

May get deposited at the electrode surface.

May go out in the form of gaseous products.

May get dissolved into the solution as ions.