Arrhenius theory of electrolytic dissociation
Postulates of Arrhenius Theory of Electrolytic Dissociation
In the 1880s, Svante Arrhenius set the foundation for the theory of electrolytic dissociation and awarded the Nobel Prize in 1903 for this theory. The main postulates of Arrhenius theory of electrolytic dissociation are given below-1. Electrolytic molecules in aqueous solution can undergo spontaneous and automatic dissociation into electrically charged particles called ions; positive and negative particles are called cations and anions respectively.
Example- NaCl(aq) → Na+ (aq) + Cl-(aq)
2. Since an electrolytic solution as a whole is electrically neutral, hence the total charge carried by cations is equal to the total charge carried by anions.
3. At moderate concentration, the ions and unionised electrolytic molecules are in dynamic equilibrium.
4. Ions are carriers of electricity, hence only such compounds which ionise in aqueous solution can conduct electricity. The conductance depends upon the number of ions; greater the number of ions, greater is the conductance.
5. The ratio of number of ionised electrolytic molecules to the total number of electrolytic molecules is called the degree of dissociation (α). The degree of dissociation decides the strength of electrolytes.
6. Ions are just like electrolytic molecules, hence electrolytes have abnormally high values of colligative propeties.
7. The properties of ions are the properties of electrolytes.
Limitations of Arrhenius Theory of Electrolytic Dissociation
Followings are some limitations of Arrhenius theory of electrolytic dissociation-1. Ostwald dilution law which is outcome of this theory fails completely to explain the behaviour of strong electrolytes.
2. As strong electrolytes are good conductors in molten state too, hence their ionisation must have taken place even in absence of water.
3. Organic solvents have not been explored as much as non-organic solvents.
4. This theory does not offer satisfactory explanation for the ionisation of electrolytic molecules in aqueous medium.
5. The observed degree of dissociation values are fairly good for uni-univalent electrolytes but fail completely in other cases.
6. This theory tell us that ions exist independently. Therefore, it overlooks the possibility of inter ionic effect.
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