Arrhenius Theory of Ionization: Week Electrolytes

Arrhenius Theory of Ionization: Week Electrolytes

From the conductance data of Kohlrausch and the fact that molar conductance increases with decrease in concentration (or increase in dilution) led Arrhenius to propose a new theory of electrolyte solutions. He proposed that in a solution of an electrolyte, ions are always present in equilibrium between the undissociated molecules and the ions in solution. Thus for the undissociated molecules AB and the corresponding ions A⁺ and B^-  (for 1:1 electrolyte) the following equilibrium exists.

AB  A⁺ + B^-                                                                                                     (12)

As the dilution increases the equilibrium lies further to the right and hence more ionization occurs. At infinite dilution, ionization is complete. Since_m  is a measure of conductance at infinite dilution, it may be interpreted as a measure of the total number of ions produced at infinite dilution. Similarly _m is the number of ions produced at some concentration C.

The ratio of _m at any concentration to _m at infinite dilution may be represented by;

_{m /m}

where  called the degree of ionization, is the fraction of the solute molecules which have ionised.

According to Arrhenius theory, all strong acids and bases are almost completely dissociated at all concentrations. The theory explains the constant heat of neutralization between strong acids and strong bases since neutralization is simply the reaction represented by the equation;

H _(aq) + OH_(aq) ------> H₂O_(l)