Arrhenius Theory of Electrolytic Dissociation

Arrhenius theory can be narrated as follows:

1. When dissolved in a polar solvent, the electrolyte splits up into two oppositely charged particles called ions. The process of splitting is called electrolytic dissociation. Positively charged particles are called cations. Negatively charge particles are called anions. The ionic dissociation of potassium chloride is given by, KC1 → K+ + C1–

2. In a solution of an electrolyte, the total positive charge over cations is equal to the total negative charge over anions. Hence, solution is over electrically neutral.

3. Due to their opposite charge, some of the formed cations and anions combine again to give back the original electrolyte. Hence, dissociation is a reversible reaction and an equilibrium is set in between undissociated electrolyte and its ions. The state of dynamic equilibrium can be represented by, KC1 = K+ + C1–

4. As dilution increases, the degree of dissociation also increases until at infinite dilution, all the molecules would be ionized and the degree of dissociation is 100%.
The degree of dissociation is defined as the ratio of the dissociated molecules in a solution to the total number of molecules, if none were dissociated.

5. The dissociation of electrolytes in the act of solution is explained on the basis of electrostatic forces. The atoms of a molecule are held together by electrostatic forces of attraction. When the salt is immersed in a solvent, due to the high permittivity of the solvent, the electrostatic forces of attraction between the atoms are weakened. This results in the separation of the atoms.

6. The ions in the electrolyte are free to move about in a random manner before an external PD is applied. The application of the external PD merely directs the movement of the charged ions towards the respective electrodes. The positively charged ions (cations) move towards the cathode and the negatively charged ions (anions) move towards the anode. The charges carried by the ions are given to the electrodes. This explains electrolytic conduction and electrolysis.

Electrical conductivity of an electrolyte depends upon the number and nature of ions.