. Conductivity of electrolytic solution We have already learnt that when an electrolyte such as sodium chloride, potassium chloride etc... is dissolved in a solvent like water, the electrolyte is completely dissociated to give its constituent ions (namely cations and anions). When an electric field is applied to such an electrolytic solution, the ions present in the solution carry charge from one electrode to another electrode and thereby they conduct electricity.
The conductivity of the electrolytic solution is measured using a conductivity cell. (Fig . ) A conductivity cell consists of two electrodes immersed in an electrolytic solution. It obeys Ohm's law like metallic conductor.
i.e., at a constant temperature, the current flowing through the cell (I) is directly proportional to the voltage across the cell (V). i.e., I V α (or) I = V R V = IR ⇒ .....( . ) Where ‘R’ is the resistance of the solution in ohm (Ω) Here the resistance is the opposition that a cell offers to the flow of electric current through it. Platinium electrode (Area-A) Electrolytic solution Figure .
conductivity cell XII U9 Electro XII U9 Electro - - - - Resistivity ( ) ρ Let us consider a conductivity cell in which the electrolytic solution is confined between the two electrodes having cross sectional area (A) and are separated by a distance ‘ l ’ . Like the metallic conductor, the resistance of such an electrolytic solution is also directly proportional to the length ( l ) and inversely proportional to the cross sectional area (A). R A R = A α ρ l l ( . ) Where ρ (rho) is called the specific resistance or resistivity, which depends on the nature of the electrolyte.
If l A m - , then, ρ = R . Hence the resistivity is defind as the resistance of an electrolyte confined between two electrodes having unit cross sectional area and are separated by a unit distance. The ratio l A is called the cell constant, Unit of resistivity is ohm metre (Ωm). Conductivity It is more convenient to use conductance rather than resistance.
The reciprocal of the resistance 1R