Arrehenius theory of ionization

Arrhenius theory of ionization consists of the following postulates.

The substance called electrolytes are believed to contain electrically charged particles called ions. These charges are positive for H+ ion or ions derived from metals and negative for the ions derived from non-metals. Number of electrical charges carried by an ion is equal to the valency of corresponding atom.

Molecules of electrolytes (acids, bases and salts) dissociate into oppositely charged ions on dissolution in water, e.g.

NaClNa+ +Cl- HCl H+ +Cl- NaOH Na+ + OH-

The number of positive and negative charges on the ions must be equal so that the solution as a whole remains neutral.

In solution, the ions are in a state of disorderly or random motion. Upon colliding they may combine to give unionized molecules. Thus ionization is a reversible process in which the solution contains ions of electrolyte together with unionized molecules.

H2SO4(aq) 2H+(aq) + SO4-2(aq)

The extent of ionization or the degree of ionization depends upon the nature of electrolyte.Strong electrolytes such as HCl etc. ionize completely in water. Weak electrolytes such as acetic acid (CH3COOH) ionize only slightly

Ionization is not affected by electric current.

When electric current is passed through an electrolytic solution, charges move towards their respective electrodes, i.e. cations towards anode and anions towards cathode.When these ions reached their respective electrodes, they change into neutral species by the gain or loss of electron.

The dissociation of electrolyte depend upon Nature of electrolyte Degree of dilution Temperature

The electrical conductivity depends upon : The number of ions present in the solution Speed of ions