Electrolytic Conduction

When electricity is passed through an aqueous solution, it may or may not conduct current. The chemical substances whose aqueous solutions conduct electricity are called electrolytes and those which do not conduct current are called as non-electrolytes. This phenomenon of conduction of current through a solution is called electrolytic conduction.

Electrolytic conduction takes place due to the movement of cations and anions in a solution. The electrical conductance of a solution, depends upon

  • (a) nature of solute
  • (b) valency of its ion
  • (c) the concentration in solution
  • (d) the temperature

Conductance and Conductivity

Like solid conductors, electrolytic solutions also obey Ohm’s Law. When a current of I amperes flows through a solution which offers a resistance of R ohms and a potential difference of V volts is applied, then according to ohm’s law

V = I . R

If the solution is taken in a conductivity cell which has two parallel electrodes l cm apart and each having an area of cross section A cm2, the resistance R of the electrolyte is found to be directly proportional to land inversely proportional to A.

R ∝ l/A

R = ρ . l/A

Where ρ "rho" is a constant of proportionality and is called specific resistance or resistivity. It is characteristic of the nature of electrolyte, its concentration and temperature.

The conductance is reciprocal of resistance and the conductivity is reciprocal of specific resistance. Conductance is denoted by L and is measured in the unit of ohm–1 (Siemens, S). The conductivity is denoted by k (kappa). The conductivity (k) is expressed in S cm–1.

L = 1/R

k = 1/ρ

Molar Conductivity

The electrolytic conductivity of a solution depends on the concentration of the electrolyte in the solution. Therefore, the conductivity of an electrolyte is normally expressed as molar conductivity.

Molar conductivity is the conducting power of all the ions furnished by one mole of an electrolyte in a solution of specified concentration.

It is denoted by λm and is related to k by the relation:

λm = 1000 k/M

Where M is the molarity of the solution. Its units are S cm2 mol–1.