Variation of conductivity with concentration

of electrolytes increases with dilution.

The variation is different for strong and weak electrolytes.

Strong Electrolytes

It is given according to the equation

are the molar conductance at a given concentration and at infinite dilution (respectively). b is a constant depending on the viscosity of the solvent. The graph shows that decreases as the concentration increases.

fig 5.6

This is because at higher concentration there is greater inter ionic attraction which retards the motion of the ions as conductance falls is that conductance at infinite dilution where the ions are far apart and there is no inter-ionic attraction. This can be obtained by extrapolation of the graph to zero concentration.

Weak electrolytes

A weak electrolyte dissociates to a much lesser extent so its conductance is lower than that of a strong electrolyte at the same concentration.

fig 5.7

The very large increase at infinite dilution is because the ionization increases and so the number of ions in solution increases.

The value of cannot be obtained by extrapolation as can be seen on the graph. It is obtained by applying Kohlrausch's law.

values for strong electrolytes is larger than weak electrolytes for the same concentration. Increase for strong electrolyte is quite small as compared to that for weak electrolyte.