Introduction to Electrolysis

The process of chemical decomposition of an electrolyte in solution or molten state by passing electric current is called electrolysis. For example: Acidified water can be decomposed into hydrogen and oxygen by the passage of electricity.

Some terms used in electrolysis:

  • Electrolytic cell: The vessel or the apparatus used in electrolysis process is called electrolytic cell.
  • Electrodes: The metallic rods that are dipped into the electrolytic solution are called electrodes.
  • Anode and cathode: The two electrodes are connected to positive and negative ends of the battery during the process of electrolysis. The electrode connected to the positive terminal of the battery is called anode and the electrode connected to the negative terminal of the battery is called cathode.
  • Anion: The negatively charged ion which move towards the anode during electrolysis are called anions.
  • Cation: The positively charged ions which moves towards the cathode during electrolysis is called cation.

Mechanism of electrolysis: 

The mechanism of electrolysis is explained on the basis of ionization theory. According to this theory, the molten electrolyte decomposes into negative and positive ions. The positively charged ions are called cations and the negatively charged ions are called anions. When electric current is passed through the solution, the electrons move from negative terminal of the battery through metal wire to the cathode. The cation moves towards the cathode by accepting electron thereby changing itself into neutral atom. While anion migrate to the anode and by losing electron thereby changing itself into neutral atom. This movement of ions is responsible for the conduction of electricity. This conduction is also known as electrolytic conduction.

Electrolysis of sodium chloride

Let us consider a electrolysis of Sodium chloride (NaCl).

The electrolytic reaction of sodium chloride is shown below:

$\ce{NaCl <=> Na+ + Cl-}$

At cathode, $\ce{Na+ e-<=> Na}$

At anode, $\ce{Cl- – e- <=> Cl}$

$\therefore Cl + Cl \rightarrow Cl_2$

Here, sodium metal is deposited at anode and chlorine is deposited at cathode.

For the electrolysis process, suitable condition and criteria should be provided to obtain the desired product.

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