Electrolysis : -

Electrolysis is defined as a process of decomposing ionic compounds into their elements by passing a direct electric current through the compound in a fluid form. The cations are reduced at cathode and anions are oxidized at the anode. The main components that are required for conducting electrolysis are an electrolyte, electrodes, and some form of external power source is also needed. Additionally, a partition such as an ion-exchange membrane or a salt bridge is also used but this is optional. These are used mainly to keep the products from diffusing near the opposite electrode.

An acidified or salt-containing water can be decomposed by passing electric current to their original elements hydrogen and oxygen. Molten sodium chloride can be decomposed to sodium and chlorine atoms.

Electrolysis is usually done in a vessel named ‘electrolytic cell’ containing two electrodes (cathode and anode) connected to a direct current source and an electrolyte which is an ionic compound undergoing decomposition, in either molten form or in a dissolves state in a suitable solvent. Generally, electrodes that are made from metal, graphite and semiconductor materials are used. However, the choice of a suitable electrode is done based on chemical reactivity between the electrode and electrolyte as well as the manufacturing cost.

Electrolytic Process :-

In the process of electrolysis, there is an interchange of ions and atoms due to the addition or removal of electrons from the external circuit. Basically, on passing current, cations move to the cathode, take electrons from the cathode (given by the supply source-battery), and is discharged into the neutral atom. The neutral atom, if solid, is deposited on the cathode and if gas, move upwards. This is a reduction process and the cation is, reduced at the cathode.

At the same time anions, give up their extra electrons to the anode and is oxidized to neutral atoms at the anode. Electrons released by the anions travel across the electrical circuit and reach the cathode completing the circuit. Electrolysis involves a simultaneous oxidation reaction at anode and a reduction reaction at the cathode.

For example, when electric current, is, passed through molten sodium chloride, the sodium ion is attracted by the cathode, from which, it takes an electrode and becomes a sodium atom.

Chloride ion reaches the anode, gives its electron, and become chlorine atom to form chlorine molecule.

$Na^+$(in electrolyte) + $e^–$(from cathode) → Na …. At Cathode

$Cl^–$(from electrolyte) → $e^–$ + Cl → $Cl_2$ …. At Anode

Electrolysis process, while useful to get elemental forms from compounds directly, it can also be used indirectly in the metallurgy of alkali and alkaline earth metals, purification of metals, deposition of metals, preparation of compounds etc.

Factors Affecting Electrolysis :-

The factors that may affect the electrolysis are;

i) The nature of the electrode

ii) Nature and state of the electrolyte

iii) Nature and electrode potential of ions present in the electrolyte and

iv) Overvoltage at the electrodes.

Electrolysis Applications :-

Electrolysis, as stated above, is a process of converting the ions of a compound in a liquid state into their reduced or oxidized state by passing an electric current through the compound. Thus, electrolysis finds many applications both in experimental and industrial products. Some of the important ones are:

1) Determination of equivalent eight of substances.

2) Metallurgy of alkali and alkaline earth metals.

3) Purification of metals.

4) Manufacture of pure gases.

5) Manufacture of compounds like sodium hydroxide, sodium carbonate, potassium chlorate etc.

6) Electroplating for corrosion resistance, ornaments etc.